NASA-CR-198849

FINAL REPORT NAG1.1174

to the

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

by the

Department of Physics

and the

McDonnell Center for the Space Sciences

Washington University

St. Louis, MO 63130

Title: Analysis of LDEF Experiment A0187-2 Chemical and Isotopic

Measurements of Micrometeoroids by Secondary Ion Mass Spectrometry

Principal Investigator:

Name: Ernst Zinner

Research Professor of Physics

Soc. Sec. #:

Fax: 314-935-4083

E-mail: ekz@howdy

Endorsements:

Principal Investigator Department Head

Name: Ernst Zinner Clifford M. Will

Signature: .!^ ) I ,- -/".

Tide: Director

C

Chairman

Telephone: 314-935-6240 314-935-6276

Fax: 314-935-4083 314-935-6219

I

(NASA-CR-198849) ANALYSIS OF LDEF

EXPERIMENT A0187-2 CHEMICAL AND

ISOTOPIC MEASUREMENTS OF

MICROMETECROIDS BY SECONDARY ION

MASS SPECTROMETRY Final Report

(Washi ngton Univ.) 68 p

Institutional

Adminj4hatiop Official

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Dir-6tFor,Spon ored^

Projects SeVip e s

314-935-6950

314-935-5862

N95-32913

Uncl as

/4^90-57

WIS

G3/90 0056857
FINAL REPORT

NASA NAG1-1174

This grant was awarded to enable the analysis of experiment AO187-2 that was flown on

board the Long Duration Exposure Facility (LDEF). The results of our work are presented in three

scientific papers (1-3) and four abstracts (4-7) copies of which are attached to this report. These

publications describe the experiment and analyses in detail and we here only summarize the major

conclusions.

The spacecraft was originally scheduled to remain in orbit about one year, but its recovery

was delayed due to the Challenger disaster and it actually spent 69 months in near-earth orbit,

being recovered just prior to the time when it would have re-entered (catastrophically) on its own.

Experiment AO187-2wvas designed to measure the chemical and isotopic compositions of

interplanetary dust impinging on the spacecraft from outer space. Information on the nature and

composition of orbital debris was also anticipated The spacecraft maintained a constant orientation

with respect to its velocity vector thereby defining leading and trailing edges that faced respectively

into and away from the direction of motion. Arrays of individual capture cells each 80.8 cm2 in

size and totaling 237 in number were exposed on both the leading and trailing edges of LDEF.

Each cell consisted of a pure Ge target surface slightly separated from a thin (2.5 μm) metallized

plastic "entrance foil." The basic concept was that incoming projectiles would penetrate the foil,

strike the Ge target plate at high velocity producing a vapor-liquid cloud that would re-deposit

material on the underside of the plastic foil. This material would then be analyzed using the

sensitive surface analysis technique of Secondary Ion Mass Spectrometry (SIMS).

In practice, most of the plastic entrance foils failed during the extended period of orbital

exposure probably due to a combination of UV embrittlement, large densities of impact events and

(for the leading edge) the effects of atomic oxygen erosion in orbit. However the foils failed

gradually and most remained in place on the capture cells for a significant fraction of the duration

of the flight. Because most of the impactors were small (<10 μm) they were heated and dispersed

in traversing the entrance foils producing clouds of molten droplets and vapor that produced easily

identifiable "extended impacts" on the Ge target plates. Fortunately, it proved possible to make ion

probe measurements of projectile compositions from material deposited on the Ge in the extended

impact structures.

In what follows, we first summarize the salient scientific results obtained from AO187-2.

We then describe an extension of this work to the analysis of impacts on flat Au targets that were

used in a closely related experiment AO187-1 whose PI is F. Horz of the Johnson Spacecraft
2

Center. In a development potentially relevant to future flight experiments, we next describe how it

is possible to determine impactor trajectories by comparing the erosion patterns produced by atomic

oxygen with the geometry of the extended impacts. As part of this grant, we received a supplement

from a Special Investigators Group (SIG) to devise and construct a novel ion imaging system for

the SIMS instrument. While this system did not lead to better isotopic analyses of the LDEF

impacts as we had hoped, we show briefly how it has proven enormously valuable in the closely

related study of cosmic dust supported by NASA in its Planetary Materials Program.

The analysis of AO187 was terminated by NASA before all the information could be

extracted from the LDEF materials. In a final section, we underscore the importance of preserving

the experimental materials for future studies and describe the current state of the materials and our

plans for their future safekeeping.

We note in passing that nine of the capture cells were transferred to scientists at the MBB

company in Munich, Germany, as per the attached letters of agreement with MBB negotiated by

NASA and ourselves in 1990. As far as we know these cells have not been analyzed using

appropriate experimental techniques.

MAJOR RESULTS FROM AO187 -2

1. The basic capture cell design worked successfully. As long as the entrance foils stayed in

place projectile particles produced "extended impacts" that could be successfully analyzed by

ion probe mass spectrometry (SIMS).

2. Even in the cases (the majority) where the entrance foils failed during flight, "extended

impacts" registered on the Ge target plates gave sufficiently intense SIMS signals to permit

elemental analyses of the projectiles. In contrast, SEM-EDS signals were not found for these

same impacts showing that SIMS was essential for the analysis.

3. Measurement of over 60 extended impacts showed that at least 75% of the trailing edge

events were produced by cosmic dust particles whereas virtually all the leading edge impacts

were produced by man-made orbital debris.

4. The very thin deposits found in AO 187-2 precluded measurements of isotopic ratios in all

save one of the extended impacts using the SIMS technology available to us at the time. An

attempt to devise an improved method for isotopic measurements of thin deposits using ion

imaging was not successful.

5. Most extended impacts have compositions that differ markedly from those measured for IDPs

collected in the stratosphere. The differences are consistent with volatile/refractory element

fractionation affecting particles with cosmic compositions. This effect had previously been

seen by us in simulation experiments of hypervelocity impacts, but is more pronounced in the
3

LDEF data, probably due to the high velocities of the impactors. Elemental fractionation in

the impact process itself represents the largest single impediment to accurate measurement of

^qr jectile chemistry:

6. Contamination of initially clean Ge surfaces during exposure in space was also found to be a

significant effect limiting the ability to make accurate measurements of projectile chemistry.

The source of the Si background seems to be outgassing from RTV, but other contaminant

sources, contributing elements such as Mg and Al, are still unidentified.

RELATED STUDIES OF FLAT PLATE IMPACTS ON A0187-1

In reference 3 and in a separate final report for NASA grant NAG 9-684, we describe our

closely related SIMS work on impacts registered in flat sheets of gold in experiment AO 187-1 ( F.

Horz, Johnson Space Center, PI). By pushing the target from the back against a flat plate, it was

possible to create a geometry suitable for SIMS analysis. In some low velocity impacts it was

possible to obtain good isotopic data on distributed chunks of projectile material. No isotopic

anomalies were found in C, N, Mg, or Si. This is not inconsistent with measurements on

interplanetary dust particles collected in the stratosphere where large anomalies are common in H

and to a lesser extent in N but not in C, Si, or Mg. As in the case of A0187-2, it was sometimes

possible to obtain reasonable SIMS data for which no SEM-EDS signals could be found.

TRAJECTORY DETERMINATION OF INDIVIDUAL IMPACTORS

As described in the attached extended abstract by one of our co-investigators, F.

Stadermann [7] an unexpected phenomenon caused by the interaction of atomic oxygen with

surfaces makes it possible to determine the angle of impact for certain projectiles. When a hole is

produced in the entrance foil of a leading edge cell by an impacting particle, atomic oxygen will

enter the hole with the stream direction parallel to the ram direction of the spacecraft. This

produces on the Ge a characteristic oval discoloration pattern whose center of gravity is displaced

from the center of gravity of the extended impact feature itself, the latter being determined by the

initial direction of the impactor. In the future, such measurements coupled with independent

determinations of the times at which specific events occurred could be used to determine the

absolute trajectories of individual particles which could then be correlated with the measured

compositions to give a more complete characterization of the meteoroid and debris complex.
4

DEVELOPMENT OF A NEW ION IMAGINQ SYSTEM AND ITS APPLICATION

TO COSMIC DUST STUDIES

This grant received funding from the Special Investigators Group for Meteoroid and Orbital

debris to implement a new ion imaging system for the Cameca IMS-3F ion microprobe used by us

for the SIMS analyses. It was hoped that ion images could be used to define regions of thicker

deposits for which the sequential measurement of masses could be used to obtain reliable isotopic

data. However, we were not able to use the imaging to obtain useful isotopic data on the extended

impacts.

However, the imaging system that was developed has proven enormously successful for

locating rare interstellar dust grains in acid residues of certain primitive meteorites. For example,

we were able to locate interstellar grains (as manifested by their very unusual 160/180 ratios) of

aluminum oxide even though such grains constitute only 10- 2 to 10-3 of all aluminum oxide grains

present in the mineral separates [8]. Another recent example of the power of the ion imaging

system to locate rare interstellar grains is the isolation of large numbers of X-type SiC grains for

detailed study [9].

IMPORTANCE OF PRESERVING LDEF MATERIALS FOR FUTURE

SCIENTIFIC STUDY

As we previously pointed out in Reference 3:

"The extended impacts of LDEF experiment A0187-2 that have already been partially

studied by existing SIMS techniques represent an extremely important

scientific resource for future work. In particular, some of these impacts may

make it possible to measure the isotopic composition of cometary material. Dust

particles from long-period comets encounter the earth with very high velocities and are

thus preferentially destroyed relative to slower asteroidal particles during atmospheric

entry. Cometary particles may thus be grossly underrepresented in the stratospheric

micrometeoroid collections. In contrast, high velocity particles produce extended

impacts with high efficiency and should thus be well represented in the existing

collection of capture cell impacts.

"Because of their potential scientific importance, continued care should be taken to

store the relevant surfaces of experiment AO187-2 under clean conditions so they may

be properly analyzed by future improved analytical instruments."

Attached to this final report is a current printout of the hypercard data system used to keep

track of the location and current status of various measurements on specific impacts. It is our
^k

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for L. 7^ , MBB

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MEMORANDUM OF UNDERSTANDING

PROCESSING OF CAPTURE CELLS ON EXPERIMENT S1002

1. Demount all capture cells (N = 11) with intact foils and prepare for

shipment to Washington University, St. Louis.

2. Demount an additional 57 capture cells and prepare for shipment to D, Washington University, St. Louis. /.

T"o ^3e Se /Pct- 71-c Xl';r, e df ^al Fe,h-,d v° l i

3. Leave 9 cells, J

and prepare for shipment to the Principle

Investigator, MBB.

4. Provide access to additional LDEF hardware to the TU Munchen to

study man-made and natural particle populations.

5. Document large impact feature on sandwich -baseplate and remove

from hardware in SAEF Il as part of the M&D SIG activities/sample

acquisition efforts. These materials are on loan to the M&D SIG.

After comp/etional of the analyses, the materials will be returned to

the Principle Investigator/MBB.

W. H. Kinard

LDEF Proiecx Office

Z/3/90
MEMORANDUM OF CONCURRENCE

I have read the attached Memorandum of Agreement concerning

processing of capture cells on LDEF Experiment S1002 entitled

"Investigation of Critical Surface Degradation Effects on Coatings and Solar

Cells Developed in Germany," and I concur with this agreement.

._, 023 gd

Ludwig Preuss Date

MBB Space Division
CURRENT HYPERCARD DATA PRINTOUT

7/2/95 4:35 PM 6/23/95.rev 1

Long Duration Exposure Facility

RO187-2 summary sheets

to 6/23/95

FnR Ftl. Cn2

Total cells on

cells optically analyzed to date

116 72 40

112 7 2 40

optically seen Extended impacts R

SU) sp cd ri total

157 259 32 35 483

possible extended impacts R:

Total: 204

number examined in sem: 18

number reclassified as Extended impact 8: 7

number reclassified as Extended impact B: 6

TOTRL NUMBER OF EHTENDED IMPfiCTS R:

Impacts cut out for ion probe analysis: 86

Impacts analyzed in the SEM : 136

Impacts analyzed by Ion Probe: 83

Summary of Trailing Edge Covered Cells

optically seen Extended impacts R

sw sp cd ri

4 5 5 6

possible extended im p acts R

Total: 5

number examined in sem: 1

number reclassified as Extended impact R: 1

number reclassified as Extended impact B: 0

Impacts cut out for ion probe analysis: 18

Impacts analyzed in the SEM : 41

Impacts analyzed by Ion Probe: 113
7/2/95 4:35 PM 6/23/95.rev 2

Summary of Trailing Edge Uncovered Cells

optically seen Extended impacts R

^Eu se cd ri

23 7 12 5

possible extended impacts 0

Total: 157

number examined in sem: 13

number reclassified as Extended impact fl: 5

number reclassified as Extended impact B: 3

TOTHL NUMBER OF EHTENDED IMPRCTS fi:

Impacts cut out for ion probe analysis: 43

Impacts analyzed in the SEM: 51

Impacts analyzed by Ion Probe: 40

Summary of Leading Edge Cells

optically seen Extended impacts R

sue s c ri

130 247 15 24

passible extended impacts R

Total: 42

number examined in sem: 4

number reclassified as Extended impact R: 1

number reclassified as Extended impact B: 3

TOTRL NUMBER OF EHTENDED IMPHCTS fl:

Impacts cut out for ion probe analysis: 25

Impacts analyzed in the SEM: 44

Impacts analyzed by Ion Probe: 25
7/2/95 4:35 PM 6/23/95.rev 3

6/23/95

OHtended impacts R eAtended imp acts 8

cell sw sp cd ri total sw s p

cd ri total craters

................................................................................................................................................................................. C 0 2-]-10 0 0 0 0 0 0 0 0 0 ............................... 0 . 

,1,,,,,,,,,,,,,,,,,,

....................................................................................................................................................................................................... CO2-1-11 0 0 0 0 0 0 0 0 0 0 .............. 2 .................

............................................................................................................................................................ CO2-1-12 0 0 1 0 1 0 .... .0...........0......... .0........0.......................3 ................. 

CO2-1„-13................. ................. 0 .............................................................. 0 0 0 0 ............. 0 0, ........................................ 0 0 0 ............................... 3

.................................................................................................................................... CO2-1-14 1 0 ............................ 0 0 ..................... 1 ............ 0 ... 0 0... 2 2 ............................... 2

............................................................................................................................ CO2-1-15 0 0 1 0 1 ............................... 1 0 ... ........................................ 0 2 3 ............................... 1

............................................................................................................................................................................................ CO2-1-16 0 0 0 0 0 0 0 1 0 1 ............................... 2

CO2-1„-17 0 0 0 0 0 0 0,,,,,,,,, 0 0 0 2

..................................................................................................................................................................................... C 0 2 -1-18 0 0 0 0 0 0 0 0 0 ........................... 0 .... ,,,,,,,,,,,,,,,,,, 1'

................................................................................................................................................................................. C 02-1-19 0 0 0 0 0 1 0 0 0 ............................... 1 . 4,,,,,,,,,,,,,,,,,,

, C 0 2ZI.- 1........................................................................................ 0 0 0 0 0 ............................... 0 0,,,,,,,,, ......................................... 0 0 0 ............. 2 ..................

1.0.2.-J..-.2.0 ..................................................................................................................................................... 1 0 0 0 1 0 0 0 1 ............................... 1 1,,,,,,,,,,,,,,,,,,,

...................................................................................................................................................................................... c e 2-1-2 e e e 0 e 0 0 0 0 ........................... 0 1 ,,,,,,.,,,. ....

........................................................................................................................................................................................................ CO2-1-3 2 0 0 0 2

IA

1 0 0 1 2 ............................... 0

CO2-1-4 0 0 0 0 0 0 0 0 0 0 2

A A A A 2 0 0 0 2 3

6/23/95

eAtended impacts H entended im p acts 8

r PII sw sp cd ri total I sw s p cd ri total raters

................................................................................................................................................................................. CO2-1-6 0 0 0 0 0 2 0 0 0 ......................... 2 ...... . 0,,,,,,,,,,,,,,,,

............................................................................................................................................................ C 0 2 I.-I 0 0 0 0 0 0 0 ............................... 0 0 0,,, ...................... 0.................

..................................................................................................................................................................................... C 0 2 -1-8 1 0 0 0 1 0 0 0 0 ........................... 0 1,,,,,,,,,,,,,,,,,, ....

CO2 -, 1„-9...................................................................................................................................................... 0 0 0 0 0 0 0 0 0 ............................... 0 I..................... 3

............................... ce2- ....................... 2-1...0 .....................0 ............... 0 ........ ..... 0 ......... ...1 ............ ....1 .................. ..... 0 .................0..............0 ......... 0 ...........0..................... 2

. ............................................................................................................................ ce2-2-11 1 0 0 0 1 ............................... 0 0 ... ..................................... 0 0 0 ............................... 2

,CO2.-.2-.1.2........................................................................................................................................................................ c e 1 2 1 4 0 0 1 2 3 ............................... 0

1.0.2.-2-1.3. 1 0 0 0 1 0 0,,,,,,,,, 0 0 0 1

....................................................................................................................................................................................................... CO2-2-14 1 0 0 0 1 0 0 0 0 0 .............. 2 .................

CO2-2- 15. .................................................................................... 0 0 0 0 0 .......................I....... 0 0 ........................................ 0 2 2 ..I...................I........ 5

....................................................................................................................................................................................................... CO2-2-16 1 0 0 0 1 0 0 0 2 2 .............. 2.................

1.0.2.-2-1.7 ................................................................................... 0 0 1 0 1 ............................... 9 0,,,,,,,,, ........................................ 0 0 0 ............................... 0

CO2-2-1....... ............................................................................. 0 0 1 0. 1 .................I............. 1 0 , ............. 0 .. ......................... 0 1 ............................... 2

1.0.2.-Z-1.9 ................................................................................... 0 0 0 0 0 ............................... 0 0,,,,,,,,, ........................................ 0 0 0 ............................... 2

CO2-2-1........................................................................................ 0 0 0 0 0 ............................... 0 0, ........................................ 0 1 1 ............................... 2

CO2-2-20 0 0 0 0 0 0 0 0 0 0 5
7/2/95 4:35 PM 6/23/95.rev 4

entended impacts H

cell I"sw sp cd ri tots

to 6/23/95

entended impacts B

A sw sp cd ri total raters

, CO2,-2-2............................................................................................................................................................................ 0 0 0 0 0 0 0 0 0 0 ............................... 2

,CO2,-2-3............................................................................................................................................................................ 0 0 0 0 0 0 0 0 0 0 ............................... 1

, C 0 2,-,2-4............................................................................................................................................................................ 1 0 0 0 1 0 0 0 l 1 ..............

1 .................

CO2-2-5.. .......................................................................................................................................................................... 1 0 0 0 1 0 0 0 1 1 .......................I....... 3

,CO2,-2-6..................................... 0 0 ................................................................................................................................... 0 0 0 0 0 0 0 0 .............1 ..................

............ CO2 -2-7............................................................................................................................................................................ 0 0 0 0 0 0 0 0 0 0 ............................... 5

.0 0 2.-2- 8.................................................................................... 1 0„ 0 1 2 ............................... 0 0,,,,,,,,, ........................................ 0 1 1 ............................... 0

,Ce2,-2-9............................................................................................................................................................................ e 0 0 0 0 0 0 0 0 0 ............................... 4

, E,03,-,1 „-14............................................................................................................................................................................. 0 0 0 0 0 0 1 0 0 1 ............................... 1

E03-1-15 C

IA ....................................................................................................................................................................................................... 0 2 0 0 2 0 3 0 2 5 ..............0.................

............... E0 3 -, 1............................................................................................ -2 2 0 0 0 1 ............................... 0 0,,,,,,,,, ........................................ 0 0 0 .............1 ..................

, E, 03,-,1- 2 ................................................................................................ 3 0 0 0 0 0 ............................... 0 0,,,,,,,,, ........................................ 0 1 1 ............................... 4

E03-1 ................... „-24 0 0 0 0 0 0 0 0 0 0 3

J.0.3.-I.-.2 ................................. C 1 ............................... 0 0 1„ ................................. 2 0,,,,,,,,,,,, ...................................................... 0 0 1 1 ..............0.................

....................................................................................................................................................................................................... 1.03-1-30 0 1 0 8 1 0 0 0 2 2 .............. 3 .................

E03-1„-,31 C 0 0 0 0 0 0 1 0 0 1 ..0...

Ss” marU of data -analUzed

entended impacts B

cell rsw sp cd ri tots

to 6/23/95

entended impacts B

I I sw sp cd ri total raters

,E03,-, 1 „-32........................................................................................................................................................................ 0 0 1 0 1 0 0 0 0 0 ............................... 2

,E,03-, 1 „-33.................................................................. C 1 0 0 0 ............................... 1 0,,,,,,,,,,,, ...................................................... 0 0 1 1 ............................... 0

....................................................................................................................................................................................................... E03-1-39 1 0 0 0 1 0 0 0 0 0 .............. 2 .................

....................................................................................................................................................................................................... 1.03-1-3 0 0 0 0 0 0 0 0 2 2 .............1 ..................

E03-1-40 0 0 1 ....................................................................................................................................................................................................... 0 1 0 0 0 0 0 .............. 2.................

....................................................................................................................................................................................................... E03-1-41 0 0 0 0 0 0 0 0 0 0 .............. 0 .................

....................................................................................................................................................................................................... E03-1 -42 0 0 1 0 1 0 1 0 0 1 .............. 0 .................

....................................................................................................................................................................................................... 1.03-1-5 0 0 0 0 0 1 0 0 0 1 ............................... 5.

....................................................................................................................................................................................................... E03-1-6 1 0 0 0 1 0 0 0 0 0 .............. 7 .................

....................................................................................................................................................................................................... E03-1-8 0 0 0 0 0 0 0 0 1 1 .............. 0 .................

....................................................................................................................................................................................................... E03- 2 -10 0 0 0 0 0 0 0 0 0 0 ............................... 5

....................................................................................................................................................................................................... E@3-2-11 C J. 0 1 0 2 0 2 0 1 3 .............. 0.................

............ E03-2-12 ... ... .. . ... ................................................................................................................................... ... ............ 1 ... 1 0... ... 0 2... 4... 1. 1 3.............. 9 ............................ 2...

......................................... E03-2-13 .............................................................................................................................................................. 0 0 0 0 0 0 1 0 2 3 ............................... 0

....................................................................................................................................................................................................... E03-2-16 0 0 0 0 0 0 2 0 0 2 ............................... 2

E03-2-17 0 0 0 0 0 0 0 0 0 0 1
7/2/95 4:35 PM 6/23/95.rev 5

summarM of data analUzed

eHtended impacts H

cellsw sp cd ri tote

6/23/95

eHtended imliocts 8

I sw sR cad ri total raters

....................................................................................................................................................................................................... E03-2-18 0 0 0 0 0 1 26 0 0 Z7 ............................... 2

............ ............................................................................................................................................................................................ E03-2-19 1 0 0 0 1 0 0 0 0 0 ..............0.................

...................................................................................................................................................................................................... E03-2-20 0 0 0 0 0 0 2 0 1 3 ............................... 3

....................................................................................................................................................................................................... 1.03-2-25 @ 0 0 0 0 0 0 0 0 0 ............................... 1

........................................................................................................................................................................................................ E03-2-26 0 0 0 0 0 0 3 0 1 4 .............. 2 .................

X.03-2-27 ............................................................................I..@ 0 0 1 .......................................................................................................................................................................................................... 0 i 0 0 0 0 0 ............................... 1

E03 -2-28 1 1 ...................................................................................................................... 0 2 0 0 1 1 2 ............................... 0

....................................................................................................................................................................................................... E03-2-29 @ 0 0 0 0 1 @ 0 0 1 .............. 2 .................

....................................................................................................................................................................................................... E03-2-34 0 0 0 0 0 0 2 0 0 2 .............. 2 .................

....................................................................................................................................................................................................... E03-2-35 0 0 0 0 0 0 1 1 1 3 ............................... 1

....................................................................................................................................................................................................... 1.03-2-36 0 0 0 0 0 0 1 0 0 1 .............1 ..................

....................................................................................................................................................................................................... E03-2-37 2 0 0 0 2 0 0 0 2 2 .............. 7 .................

..... E03-2-38 ................................................................................................................................................................................................... 0 0 0 0 0 0 @ 0 1 1 ............................... 6

....................................................................................................................................................................................................... E03-2-9 0 1 0 0 1 0 0 0 0 0 ............................... 7

....................................................................................................................................................................................................... E03-3-43 0 0 1 0 1 0 1 0 0 1 ............................... 6

1.03-3 -44 0 0 0 0 8 0 0 0 0 0 0
7/2/95 4:35 PM 6/23/95.rev 6

Su MarM of data analUzed

extended impacts R

cell rsw SP cd ri tot€

to 6/23/95

extended imp acts 8

I sw sP cd ri _ total raters 1.01-4.-49.................... ................................................................... 0 0 0 0 0 ............................... 0 0,,,,,,,,, ........................................ 0 0 0 ............................... 2

........................................................................................................................................................................................................ E03-4-50 0 0 0 0 8 0 2 0 1 3 ............................... 0 E03,-4-56............................................................................................................................................................................. ...............................

T.01-4.-57 0 0 0 0 0 0 0,,,,,,,,, 0 1 1 4

,E,03„-4, .... -5........................................................................................ 8 0 0 0 0 0 ............................... 0 0,,,,,,,,, ........................................ 9 0 0 ............................... 0

....................................................................................................................................................................................................... E03-4-59 0 1 0 0 1 0 2 0 1 3 .............1 ..................

,E,03,-4,-,6,0 0 0 0 0 0 0 0,,,,,,,,, 0 1 1 1

E,0 3,-4,-,6 ........................................................................................ 5 0 0 0 0 0 ............................... 0 0,,,,,,,,, ........................................ 0 0 0 ............................... 1

....................................................................................................................................................................................................... E03-4-66 0 0 0 0 0 0 0 0 0 0 ............................... 3

........................................................................................................................................................................................................ E03-4-67 1 0 0 0 1 0 0 0 0 0 ............. 0.................. E 0 3 -4 - 6 8 .................................................................................... 0 0 0 0 0 ............................... 0 0,,,,,,,,, ........................................ 0 0 0 .............. 4 .................

....................................................................................................................................................................................................... E03-4-69 0 0 0 0 0 0 0 0 0 0 ............................... 1

........ ............ ................................. E03-4-74 0 ............... 0 ............. 0 .............0................0 ......................0 .................0..............0......... ............... 0 0..................... ...................... 0

................................................ E0 3 -4-75 C ....................................................................................................................................................... 0 2 0 8 2 0 0 0 0 0 ............................... 0

....................................................................................................................................................................................................... E03-4-76 C 0 0 0 1 J. 0 0 0 1 1 ............................... 0

E03-4-77 0 1 0 1 2 0 0 0 1 1 0

extended impacts H

cell rsw sp cd ri totz

to 6/23/95

extended impacts 8

I sw sp cd ri total raters

....................................................................................................................................................................................................... E08-1-10 0 8 0 0 0 0 1 0 0 1 ............................... 73

....................................................................................................................................................................................................... E08-1-12 1 5 0 0 6 0 9 0 0 9 ............................... 48

E08-1-13 0 1 0 0 1 0 0 0 0 0 1.0 .............

E08-1-14 1 2 0 0 3 1 2 0 0 3 .3 .6 .............

........................................................................................................................................................................................................ E08-1-15 0 2 0 0 2 0 1 0 0 l ............................... 64

E08-1-16 0

IA

....................................................................................................................................................................................................... 0 0 0 0 0 1 1 0 2 ............................... 95

.................................................................................................................................................................................................. E08-1-17 0 0 0 0 0 2 0 0 2 .................. 6.......... 2

....................................................................................................................................................................................................... E08-1-18 0 0 0 0 0 0 0 0 0 8 .................. 8 6.............

....................................................................................................................................................................................................... E08-1-19 2 0 0 0 2 0 1 0 0 1 ............................... 34

....................................................................................................................................................................................................... E08-1-1 0 3 0 0 3 1 2 0 0 3 ............................... 51

................................ ........ E08-1-20 ..... . ............... 0 ............. 0 .............. 1 ............... 0 ........................................ 1 1 .............. 0 ............. 0 ........... 0 ......................... 1 ...................... 35

....................................................................................................................................................................................................... E08-1-2 1 5 0 1 7 0 0 0 0 0 .......I....................... 48

....................................................................................................................................................................................................... E08-1-3 2 2 0 0 4 0 0. 0 0 0 .................. 75 .............

....................................................................................................................................................................................................... E08-1-4 0 2 0 0 2 0 10 0 0 10 .................. 62 .............

....................................................................................................................................................................................................... E08-1-5 2 4 0 0 6 0 7 0 0 7 ............................... 76

E,08-1-6 0 2 1 0 3 1 1 1 0 3 45
7/2/95 4:35 PM 6/23/95.rev 7

summ-urM of data analUzed to 6/23/95

extended impacts H extended impacts 8

cell sw s p cd ri total I sw sp cd ri total raters

........................................................................................................................................................................................................ E08-1-7 0 0 0 0 0 0 0 0 0 0 ............................... 88

....................................................................................................................................................................................................... E08-1-9 2 0 0 0 2 0 0 0 0 0 ............................... 24

....................................................................................................................................................................................................... E08-2-10 0 l 0 0 1 0 2 0 0 2 .................. 6 3.............

........................................................................................................................................................................................................ E08-2-11 1 0 0 0 1 0 1 0 0 1 ............................... 41

....................................................................................................................................................................................................... E08-2-12 2 1 0 0 3 0 1 0 1 2 ............................... 56

....................................................................................................................................................................................................... E08-2-13 0 1 0 1 2 0 2 0 0 2 ............................... 39

....................................................................................................................................................................................................... E08-2-14 0 0 0 0 0 0 0 1 0 1 .................. 47.............

....................................................................................................................................................................................................... E08-2-15 2 2 0 0 4 1 0 0 0 1 ............................... 50

....................................................................................................................................................................................................... E08-2-16 0 4 0 1 5 0 2 0 1 3 ............................... 30

....................................................................................................................................................................................................... E08-2-17 0 4 0 0 4 0 0 2 0 2 ............................... 59

E08-2-18 0 4 0 0 4 0 4 0 0 4 .4.2.............

....................................................................................................................................................................................................... E08-2-19 3 2 1 0 6 0 1 1 0 2 ............................... 65

................................................................................................................................................................. E08-2-1 ...... ... ... ... .. ... ... 0... 1 0... ... 0 1 0 ... 1 ... 0 0 1 ............................... 29

....................................................................................................................................................................................................... E08-2-20 0 1 0 0 1 1 2 0 1 4 ............................... 34

....................................................................................................................................................................................................... E08-2-2 0 0 0 0 0 0 0 0 0 0 .................. 8 5.............

E08-2-3 0 2 1 0 3 0 0 0 0 0 99

su ,nmarlj of data analUzed to 6/23/95

extended impacts 8 extended impacts 8

cell sw sp cd ri total sw sp cd ri total c raters

....................................................................................................................................................................................................... E08-2-4 0 0 0 0 0 0 0 0 0 0 ............................... 53

....................................................................................................................................................................................................... E08-Z-5 0 0 0 0 0 0 0 0 0 0 ............................... 100

................... E08-2,-6.................................................... 0 4 1........................... 0 ....5................. . 0............. J............0..........0....... J ........... .... ....... .^7.............

................................ E08-2,-,7..................................................... 3 0 0... ..........0............3 ..................0..............0...........2..........0........2......................52

,E,08-2 ...........

,-,8................................................... 0 3 0............................... 0 3 ................. .0............. 4...........0.. ....... .0.... ... 4.......................`..:g.............

,E08,-2-9..............................0 ................................................................................................................................................. 2 0 0 2 0 2 0 0 2 ............................... 60

E,0....8,-3. ........'..0..................2........... ............................... 4 0 1............^ ..................0..............3.......... 2.........0........5......................3 g.............

....E.... 0.... 8„- ...3 .

,-..1 ... 1................. ..... 2 ............... 6 ..........0..........0............ .. 8 ................. J.............. 4...........0......... J.........6......................4.'..............

............................................................................. E08-3-12 1 0 ..............................1 0 0 1 ..................................... 0...........0..........®............... ................58.............

E.0.8..-3,- 13 ..................2 ........................................ 1 0 1 .............4..................0..............0...........0..........3.......3......................66.............

......................0 .......... ..... 0 ............. 0 .............0............0 .................. 0..............0...........0..........0........0......................67.............

Y.O.B.-.3Z.11. 5 0 2 0 0 2 0 0,,,,,,,,, 0 0 0 85

....O.$.-3,-,1„6................................ 0 ............................... 0 0 0............®.................. 2..............0.......................0........3......................7$.............

E08-3-1 .... 

„7......................0...............0 ............. 0 .............0 ........... . 0 ................. A .............. .0 .......... .0 ......... .0 ....... .1.......................77 ... ..........

......................................... ...................... 1 ............................... 2 0 0............3 .....................................I...........®..........® ........2...................... 57.............

E08 -3-.'..9.. 2 4 0 0 6 .................. 2..............`.,:.......... 0..........2.......8......................32.............
7/2/95 4:35 PM 6/23/95.rev 8

emended impacts B

cell rMSw sp cd ri tots

to 6/23/95

entended impacts B

I I sup sp cd ri total raters

E08-3 -, 1.............................................................................................................................................................................. 1 2 0 0 3 0 0 0 0 0 ............................... 71

S.0.8.-.3.-.2.0 0 2 0 0 2 2 4,,,,,,,,, 0 1 7 3 9

, E,08-3,- 2.................................... 0 t............................... 0 0,,, ..................................................................................................... 1 0 0 0 0 0 ............................... 84

,E0,8„-3,-3.............. ....... ..... 0......... ..... 2 ............. 0 .............0................2 ......................0 .................0..............0.............0...........0....................................... 67....

E08.-3-4............................................................................................................................................................................. 1 3 0 0 4 0 4 0 0 4 ............................... 41

E08.................................

,-3-5 4 5 0 0 9 2 2 0 2 6 53

,E0.8„-3,-6........................................................................................ 0 4 0 0 4 ............................... 0 4,,,,,,,, ........................................ 1 0 5 ............................... 5 5

............................ 8,-- 7 ................................................................................... 1 2 0 0 3 ............................... 0 1 ........................................ 0 t 2 ............................... 48

,E.0,8,-3........................... -9 ............................... 0 0 0 ...................................................................................................................... 0 0 0 0 0 0 0 ............................... 31

EOB-4-.10...... ..............................I 1 .............. 6 0 .................................. 0 7 ............................... 2 2 ........................................ 0 1 5 ............................... 38

............ E 0 8„-4.............................. -11 0 .............................................................. 4 0 0 4 ............................... 0 0 ..... ........................................ 0 0 0 ............................... 44

,E0,8,-4,-12......................................................................................... 1 0 0 0 1 ............................... 0 1 ........................................ 0 0 1 ............................... 65

....................................................................................................................................................................................................... E08-4-13 2 0 0 0 2 0 0 0 0 0 ............................... 30

E08-4-, 1,4.................................................. 0 4 0 1...................... 5 ............................... 0 0, ........................................ 0 0 0 ............................... 29

............................................................................................................. E08-4-15 5 8 1 0 14 0 1 ................................... 0 1 ............................... 22

E08-4-16 0 2 1 0 3

..................................................1,11

0 1 0 0 1 20

Su marjj of data analUzed

entended impacts R

cell rsw sp cd ri tote

to 6/23/95

eHtended im p acts B

1 I sw sp cd ri total raters

,E0,8,-4-,18............... .... .......1 ..... ..........1 ........ ................... 0 0........... .. .......... ........ ... 2 1 ........................... 1 0 .. ............. 1 3......... ... ...........23..... ...... ....... ..

....................................................................................................................................................................................................... E08-4-19 3 2 0 0 5 0 2 0 2 4 ............................... 19

....................................................................................................................................................................................................... E08-4-1 1 2 0 1 4 0 1 0 0 1 .................. 45.............

....................................................................................................................................................................................................... E08-4-20 1 1 0 0 2 0 1 1 0 2 ............................... 59

....................................................................................................................................................................................................... E08-4-2 1 2 0 0 3 3 2 0 0 5 ............................... 50

E08-4-3 1 2 0 1 4 1 3 0 0 4 213 .............

....................................................................................................................................................................................................... E08-4-4 0 1 0 0 1 0 2 0 0 2 ............................... 19

........................................................................................................................................................................................................ E08-4-5 1 4 0 0 5 0 0 0 1 1 ............................... 36

E08-4-6 0 2 0 0 2 1 0 0 0 1 1.2 .............

E08-4-7 1 4 0 0 5 J. 2 1 2 6 .4 .2 .............

........................................................................................................................................................................................................ E08-4-9 0 1 0 0 1 0 1 0 0 1 ............................... 19

E08-5-10 0 1 0 0 A. 0 0 1 0 l .4 .9 .............

E08-5-11 3................................................................ 5 0 0 8 ............................... 1 ...................................................... 2 0 0 3 ............................... 66

E08-5-12 ................. 2 5........................... 0 0..... ................................... 7 2 ................ .............-.... ............................ 1.............0...............0........... 13 .............

....................................................................................................................................................................................................... E08- 5-13 0 3 0 1 4 2 l 1 3

3......................4....

7 ............................... 4 8

E08-5-14 1 1 0 0 2 1 0 0 2 3 45
7/2/95 4:35 PM 6/23/95.rev 9

S11 arU of data analUzed

eHtended impacts H

cell rsLu sp cad 

^ ri totz

to 6/23/95

eHtended im pacts 8

I I sw sp cd ri total raters

S.O.B.-.5Z.15 .1.......................................................................................... 0 0 0 0 0 ............................... 0 0,,,,,,,,, ........................................ 0 1 1 ............................... 7 Z

. E 08,- 5-, 16........................................................................................ 0 3 0 1 4 ............................... 0 2 ........................................ 0 0 2 ............................... 60

E0,8,-5-17..................................................... 8 3 0...............................„ 0 11 ....................................................................................... 0 5 0 1 6 ............................... 21

................................................................................................................................................................................. E08-5-18 3 2 2 0 7 0 11 0 0 ............................... 11 I..................... 10

....E0....................... 8 - 5 - 1 ..9 ................. .. 7 ............4........ .. 0 ...........0........... ... 1....1 .................................. ................0.................0............0......... .. 1 ........ .. 1 ...................... ..... 22....

....................................................................................................................................................................................................... E08-5-1 1 0 0 1 2 0 0 3 0 3 ............................... 59

........................................................................................................................................................................................................ E08-5-20 0 0 2 1 3 2 0 1 0 3 ............................... 56

....E0....................... 8-5-2 ..................... .. 0 ............4 .................................... ........ .. 0 ...........0.............4 ...................0 ..............4.......... .. 1 .......... .. 1..........6.......................... 45....

........................................................................................................................................................................................................ E08-5-3 1 2 1 0 4 1 3 0 0 4 ............................... 91

........................................................................................................................................................................................................ E08-5-4 0 0 0 1 1 0 0 1 0 1 ............................... 60

....................................................................................................................................................................................................... E08-5-5 1 3 0 0 4 3 6 0 0 9 ............................... 68

....................................................................................................................................................................................................... E08-5-6 0 2 0 2 4 0 1 0 0 1 ............................... 50

E08-5-7

.....................1..0

....................................................................................................................................................................................................... 6 1 0 0 7 0 4 0 1 5 ............................... 31

.................................................................................................................................................. 3 0 0 3 0 1 0 0 1 .................. 2 9.............

....................................................................................................................................................................................................... E08-5-9 2 3 0 1 6 1 5 0 2 8 ............................... 20

E08-6-10 0 4 0 0 4 0 1 0 0 1 50
7/2/95 4:35 PM 6/23/95.rev 10

summary of ext ended impacts H

as of 6/23/95

impact name type of impact size comments analysis to dote

CO2 1 15B 2 crater ..................................................................................................................................................................................................................... 3800 sem sims ...............................

E03 3 46A 1 crater ..................................................................................................................................................................................................................... 3200 sem sims ...............................

.............................................. CO2 2 17C 1 c r a t e r ....... .......... .......................................................... 3 0 0 0 crater 800 .... ...................sem ............. . . sims ..................................................

............................................................................................ CO2 1 12C 2.................. cr ate r 2400 ..... ..... c 

r.......

ater 700

............................

............................................................................. um sem s i ms . ..............................................

............................................................................ E03 1 42A 1 crater ............................... 2100 ................ crater 1000um.............

............................... .................................................................. none

....................................... ................................................... .............................. .surroundin.g.s.P.. M.... .... ..... ............................................................ ......

V.)...... 10.. u m ........................................................... ...............................

E08 2 6C r-ater ..................................................................................................................................................................................................................... 2100 caused much

19AMa

none ...............................

.................... . ...... ....................................................... ...... I ..... ........ ge........................................................................ ...............................

......................... E08 5 18A 2......................................... crater ............................... 1792 half of cr impact ............................... .................................................................. none

................... I ................... ...... ....................................................... .................... destroye.d.....edge............ ................................... ...............................

... .... ..... ..... ....cracks .............. ................ extend x.............. . 

......................................................................................................................... d......... eb.............. v ris ................. isible ...................................................................................

....................................................................................................................... ..........i............................l..l i nsde as we ...................................................... as ...............................

..................................................................................................................................................................................................................... white substance ...............................

................................................ E03 1 32B 1 c.r,ate.r .....................................1,60,0......hard.... .... ......

to judge................... none....................................................

..................................................................................................................................................................................................................... whether it is cd ...............................

......................................................................................... ............................... Rr ..... .P.. ...... P..ro,misMa ......... ..................................................................

..................................................................... ............................... ...................

for......

ion..... p,robe................... ..................................................................

..................................................................... ...............................

E03 3 43C 3 crater 1600 sem sims

summary of extended impacts A

as of 6/23/95

impact name type of impact size comments analysis to date

........................................ E08 4 16A 9 .... crater ..................................................... ....

,,,,,1344,, through.......wafer,,,,,,,,,,,,,, ................................... none ...............................

....................................... ...... ....................................................... .................... deb.... ....... ris... .......visible.................................................... ....... ...............................

....................................... ....... .............................. ..

inside. cracks..... ... . .................................. ...............................

......................................I ...... ....................................................... . ................... extend ............. some.................... .. ..

....................................................................................................................... ........b......... d e ris............................................................................. on wafer ...............................

......................................................................................... ............................... b elow .......... crater ................ .......r ... .

................................................... ..... white............... dust^ ........................ ..................................

................. E03 3 ............................... 53B 1 c,r,ate,r ......... ...................................

......................6...

......

.................................................................................................. sem

...............................

................. E08 4 ................. 15C .............. 6 c r,at e.r. ................................... 1120 .............................. ............................... sem....

...............................

sims.......................................

..................................., E03 2 11A 2 C„ crater .................................................. sem

6

1 .................................................................................................. sims ...............................

........................... CO2 2 18B............................... 1 crater...................................... ........................................ ............................... sem......................... sims

.............................................. E08 2 3D 11 crater ................................... ,900.................................................................................................... erosion too none

...............................

CO2 2 128 1 C crater ..................................................................................................................................................................................................................... 800 se 

...............................

...............................

............................................. E03 1 40B 1 c rat e r ................................... .8,0,0.................................... ............................... sem......................... sims

........................................... E03 3 61D 2 C„ crater , ................................... 800,

...................................................................................................... sem

...............................

................................... E08 6 18A 1 ..... crater ........................................... 720.. ........debris........................ mostl}( on ................................... none

...............................

...............................

......... ................................................................................... ......................edge... 

..................................... ..................................................I................ ..

............................................. E08 6 19D 10 crater .................................... 720......................................................................................................... debris extends none ...............................

................ ............................... .............. ...... .........................................................

.......................................... E03 3 71C 1 C„ crater ............................................................................... 640 se....m

............................... ............................... ..

E03 2 27D 1 crater 600

...............................

se

.......................................................

sims
7/2/95 4:35 PM 6/23/95.rev 11

summary of eHtended impacts R

as of 6/23/95

impact name type of impact size comments analysis to date

................. E03 3 62B 1 c, r,a, te. ....................................... r ................................... 5.4.0......... . ......................................................... sem....sims ...............................

....................................... CO2 2 12D 2 C„ crate....................................... r 480......... . relati„v„ely ,small sem sims

................. E08 6 13D ............................... 15 c rate r,8.0 ................................... 4 large debris............................................................... area none ...............................

E08 5 18B 3 crater ..................................................................................................................................................................................................................... 336 w/ extensive none ...............................

......................................................................................... ............................... s.RJA Y............................................................................ ...............................

......................... E08 2 19C .......... 12 crater, .................................... 300.................................................................................................... debris over wide none ...............................

..................................................................... ............................... ................... are.......... ............................................................................................................... a

..E08 ............1............ 20A.......1.. ................ crater.......................................

,2,8,0................................................................... non.......................................................

..................... E08 1 6C 8.......................c,r,ater ................................... 224 looks.........very ................................... none ...............................

..................................................................... ............................... ...................romisLM .P. A ............................................................... ...............................

E08 5 20B 6 crater ..................................................................................................................................................................................................................... 224 sem ...............................

E08 5 20C 2 crater ..................................................................................................................................................................................................................... 168 none ...............................

E08 5 3C 18 crater ..................................................................................................................................................................................................................... ?900 white substance none ...............................

....................................................................................................................... .. i....n....s..i.................................................................................. de ...............................

...................... CO22 SA .. ......................

r i.n.g ...........................................8.0.0.............. ..................................................... sem........sims.......................................

............... E03 4 77D ............................... 1 ri.n.g .................... .........................800......... . melting....zone..................... sem....Sims.......................................

E031 2A 1 C.. .. r MA ...........................................Z.2.0... .......................... ............................... Sem....s, ms.......................................

........................ E033 61 D............... 1 C...ri.n.g ...........................................7,2,0.................................... ............................... ...e m....................... ...............................

................................... E03 4 76A 3.... C...ri n.g .......................................... .................... 720 ...meltin.....?one....e................ Sem....sims..................... I.................

........................................ ...................................... .................. left ...................................................................... ...............................

summary of extended impacts H

as of 6/23/95

impact name type of impact size comments analysis to date

...................... CO2 2 1.0.g......1 ...........! i.n.g ....................................................................................................................................... .................... 0 sem sims ...............................

..............3................... E033 71 A 1 .... C.. r i n.g...............................................4 0 ............... .................................. none..................... ...............................

.......................................... E03 3 71B 1 C„ ri ng ................. .... 640 melting,,,, zone ....

,,, in................................................... sem I.........I....................

..................................................................... ............................... ................... ...........

lower left...I........................ ..................................................................

............................................. E08 6 7A 7 ri,n.g ...............................I........._ ,,,,_560 .............cr J ...... ........

. I.Ke ,damage......,,,,,,,

.................................................................. none

.....................,o bottom ...................................

tt..m . ............... . ..................................

E08 5 9B 18 rI.n .g ............. 504.............ov„eriaps erosion ....................................................

...............................

..............................1............... none

.............................................. E08 6 5B 11 r i.n.g ...............................................504.................................................................

...............................

n,o n e ......................................................

.............................................. E086 5D 10 r MA ...............................................504......... n,one....................................................

E033 62B 2 rin g ............................... 500 ...

...........................................................

.......!Mn ............... ..................... s .... n......................................................

........................................... CO2 2 12D 3 C.. ^i.n.g ...........................................4.8.0........lon.a.....tailed......., ...................................................... sem sims ...............................

..................................................................... ............................... ................... me(tin.9.....zO,ng.....................

................................ E08 1 2A 14..........

r i.n.g ...............................................448.................................. ...............................

...................... ............................................

non... e ...................... ...............................

................................................ E08 4 1C 6 r i n g 448.................................................................................................... below BED sem sims ....I..........................

..................... E086 2C 8.....................r i.n.9 ....................... .................... 448.................................. ............................... n,one.....................

E08 5 16B 4,,, ................................... .......ri,n,g ...........................

............. 420.................................................................................................... below erosion

...............................

none

.............................................. E08 4 3B 3 ri.n.g ...............................................392.................................. below BED..........I....................

...............................

n,one.....................

............................................. E086 7B 9 . r i n.g...............................................392................................. ...............................

...............................

n,one..

E033 63D i .... 0 ..........................................n.g ...........................................3.6.0......... . .........................................................

.............. ....................................

n,one.....................

,E08 3 13D 7 ............ ................. rI.n.g........... ............................... 360.... sprayx below.....................

...............................

sem ................................................................. sims

................... erosion ........................
7/2/95 4:35 PM 6/23/95.rev 12

summary of extended impacts R

as of 6/23/95

impact name type of impact size comments analysis to Mate

................................... E08 5 136 4.......... ri.n.o ......................... ..................3.6.0........ sP.raX....in....middle..........., sem....sims.......................................

.......................................................................................... ............................... ..... ri ngri n.9 ........................................................................ ...............................

E08 .................... 5 4A 6................ ri n p 3............ 60 .spray„ at ,bottom... ............... .. .......................................................... non e ......

.............................................. E08 6 13D 18 ri.n.e ...........................................360............below............ errosion ......................I........ none....................................................

..... E08 2 13D 14 1 ............... .................ri.n.g ................... ............................336.................................. non ..................................................... .51

.

E08 5 66 17 rin B ........................................ 336 .... .............. ........................... none ..............................................................

................................... E08 6 16B 5...........ri.n.a ...........................................3.3.6......... . V ery.

.......faint............................n. one .................... .................................

.............................................. E08 5 20C .. ri.n.g ................ ...........................2,8........... ...blue. .....elli.P..t.......................I... n,one.....................................................

............................. .. .............. ................... . ................................... .................... .. d............... isc. o.l..o.....r .................................................................... ...............................

. ......... E08 6...........7C.....4................ri.n.a ................... ............................280........... .................. ........................................ n,one ........................ ............................

. ......... .... ... E082............ ..... ..... 16A 17 ...... .ri.n..g ................... ............................224..... ..................................... .........................I. none....................................................

E08 3 10C 11 r i,n,B,,,,,, ,,,,,224 non e .................................................................

. ....... E08 4 14D 7 .......... ......................... .... r iAA............. ..............................2 2 4 .................. ............................ none...................................... ..............

................................................ E08 5 1D 12 ..i ..... ............. ...........................2,24 ............................................................................................................ none ...............................

E08 5 6D ...................................... 21 ri.n.S1 ...........................................2,2,4..........concentric................. rings?...... n,one....................................................

CO2 1 14C 2............spiderwe................................ b 200,Q very,

promising,,,,,,_.,,,, sem ... sin ..................... a.................

E03 1 39C 1 apiderweb ............I ...............1..60.0 ..... . sem sims .......................................

CO2 1 ................................... 20D2.......... s.pide,rwe,b ............................1 50.0 ..... . sem....sims .......................................

........................................ E03 4 56D 4 C...„ spiderweb .............................1400 ..................................................................sem s im s

E03............ 2 37A......5,,., , ..... s.P.. i d e r w e b .........I..................1..3.0.0,,,,, ............................................................. on e................ 

summary of extended impacts N

as of 6/23/95

impact name type of impact sine comments analysis to date

.............................................. CO2 18A 2 spiderweb ............................1,20,0 ................................. ............................... sem........sins

............................................. CO2 2 8D 1 spiderweb ............................1200 ................................ .............I................. sem ..... ............. sims

.................................. CO2 2 4B 1............. spiderweb ............................1„100 ..... ............................................................... sem..... sins ..

.............................................. CO2 1 3B 2 spiderweb.............................................................................................................................................. 1000 sem sims ...................I...........

CO. 2 211 . ........ .. ,A ......... 2 ....... spiderweb........................ ... ...1 ..EE ... „000.... ....................................................... .. ...... sem ........sims

......................... CO2 2 13B 1................ spiderweb.................................................. 1000 near ..... ..........

,

the edge,,,,,,,,,,,,,,,,,,, .................................................................. sem sims

.............................................. E03 1 22D 2 s,p de.rw eb ..........................1„00,0 ............................................................... sem sims ,,,,,,,,,.,,.,,,,,,,,.,.,,.,,,,,,,,.,,,

........................ E03 .. 52D 4 ..................s.piderweb................................1,0,00 .................................................................................................. material seen in sem sims ...............................

sem................................................................................. ...............................

E 03 4 67 D 1..................s p i d e, r w e b ................... ............................................ 1000 ............................... sem sims , ............. s.,,,.,,,,,,,,,,....,,,,,,,,,,,,,,,,,..

EQ3 2 11A 1 .............................I.. .... C........iderweb...........................9.6.o......... Sem....sims .......................................

............................................. E03 2 19C 1 spi..erweb ............................840.................................... .................I............I ...sem.......... sims

..................... E08 3 10B ... 13 .... ............. s,piderweb.......................... 840.................................................................................................... sem sims

.............................................. CO2 1 3C 1 spiderweb ................................................................................................................ 800 or EXT.IMPB?

....... ....... .................

sem sims

...CO2 2 14B 1 ................................. ....... R.piderweb .....800 .....250x800 Tots of

.................,...... . ....... . .............

...............................

sem sims

...................................................................... ............................... .................. c ...o..n............................. taminatio..................... n ..................................................................

...................................................... ............................... around it. .....................................................................................

,E03 2 37C 2 .................................... spiderweb............................................................................................................................................ 800

...............................

sem sims

............................................. E083 7C 17 spiderweb......................... . 784 .... .............................................................

...............................

none.....................

,E03 1 2D 2 ......................................C.. sp, iderweb ............................................. 720

...............................

sem........sims .......................................
7/2/95 4:35 PM 6/23/95.rev 13

summary of extended impacts R

as of 6/23/95

impact name type of impact size comments analysis to dote

E03 1 33C ...1 C.. s.P...ide,rweb 72,0 .............. ...................................................... E08

...

1 14C1.1 s.P..iderweb ...................... 672... sera ............................

................... ................ 1 .. ........

r,

...................... 650... m, ri

sips

Sem....m s

..................... E03 1 6!) 2.................... spide,rweb ......................... ,6,4,0...................................................................

.....................................

sem sips ..........

................................... E08 4 13B 4.......... s.P.. ide rweb ......................... ....61.6................................................................. none

. E08 6 5D 15 .............................. .......... .... spiderweb ....... .................. 616........ .................................. ...... .........................

........................................................

no ne . . E03 2 12A 3 ,,, ................................... , ......s,piderweb ...........0............. 600 .... large ,classical

............................

.........................................................

sem sims

.......... . ........... ......... .......... ...... ............ .. mat II

...... ....... .....

................................... E03 4 47B 2 ..... s p i d e r w e b............................. 600..........near the edge,,,,,,,,,,,,,,,,,,, ..... .I...........

..

non e

............................................. E08 4 2D 15 spiderweb ......................... ,600........................................ ...............................

..................................................................

none

............................................. E082 7 7 sAide,rweb ......................... .................... 560 . ..................................................

.....................................................

s.em.......................

..................... E08 2 7C........ 8 ............ s,piderweb....... .................. . 560 large scatter of .............................

...............................

. sem

..................................................................... ............................... associated .............................................................. ...............................

......................................................................................... ............................... in?.P..acts. ..... !?.e. ....................... ..................................................................

.................................................................. .......................................................residue appa,rent ......... ............. . ..... . ... .... ... ... ... .............................. .E08 4 13B 5 .............. ...............

.... spiderweb ......................... 560....................................... ............................... sem sims

................ E08......I.^A............... spiderweb ......................... 560.......

........................................................

none

............................................. E08 6 17C 15 ..... web ......................... .560......... ........................

........................................................

n,one.....................

......... E08......6......5.C..................... C 4 spiderweb ........0................ .5fi0 ........................................ ...............................

...............................

none

E08 6 5C 6 spiderweb.......................... 560.................................................................

..................................................

none ...........::....................................... .............6...6,C...................

E08 6 6C 6 s.piderweb 560 none

summary of extended impacts A

as of 6/23/95

impact name type of impact size comments analysis to date

........................I....................... CO2 2 16A 1 spiderweb................................550............. sera sims

E08 2 19A 3 spiderweb 540

..........................I........................ ............

none

.................................. ........... E08 2 15D 1 s.P...ide,rweb .......................... .504......... . n,one

.............................................. E08 3 11A16 spiderweb ................I........ . 5..0.4........

.............................•......................

none

.................................. E08 4 15D7.... ......s.P...iderweb ..I...........I........... 504....... deeP.....and .................................

..........................................I.........

none 

.....................................................

.......... .............. ... .................................... .............. crater-like............................................................ ...A.......... J.

.............................................. E08 4 19C 4

p..........r

spiderweb ......................... 504.......

...............................

none.......

.............................................. E08 5 17D 7 spiderweb ..............................504 .............

.............................................

s.em E08 6 136 2 ...P..ide, rweb .... 5.4 ..................................... 00 ..............................ne. .

......................................................

..o

.............................................. E08fi 2C 11 s...ide,rweb..............................5............ 04 ..........................................................

............................... ..................

non.... e .... ................................................ E08 2 19A 2 s,piderweb ,,,,,4 80 .............. none

E08 3 11A 21 s,pide ,rweb ...............I......... 448.................................. none

.............................................. E08 3 19C15 R.piderwe,b .......................... 448 ......

...............................

overlaps ,BED

............................................

sem sims

....................................... E084 5A 9 0......spiderweb....I..................... 448 ................................................................ none

............................................. EOS5 11A 17 spiderwe.b ..............................448....... ..........................................................

............................................I........

n.one......................

......................... E08.. 17D... .1.1........ 11 ...P...ide,rweb..........................

s.P..1448

....4 48 ............ . ..................................................I......

.......................I.......

s.em.......................

................ E08 5.... 1 9D................. 10 s.P..iderweb.......................... 448............

...............................

none

E08 6 13A 8........... .iderweb.................I....... ............

....................................................

none

.............A........ E086 17A....1.......... spiderweb......................... . ....4............ 48 ...................•.......

...................... ............................................

none.....................

............................................. E08 6 1D 6 s,piderweb 448.......................................

............................... ...............................

none

.E08 6 6C 7 ap. .!A ,rweb ....448

...............................

..........................................................

...............................................................

sem....sims.......................................
7/2/95 4:35 PM 6/23/95.rev 14

summary of entended impacts R

as of 6/23/95

impact name tripe of impact size comments analusis to dote

............................................. E03 228A 6 spiderweb .......................................................................................................................................... 420 none

................................... E08 4 20D 8 ........... §.piderweb .......................... 400...................................................................

...............................

none............ ...............................

............................................. E08 5 17D 4 s.piderweb............I............. 392 .. faint,, below.......................................................... sem ...............................

............................................................................................ .................... ero..........s......... ion

............................................... E08 5 19D 8 spideSWA.b ......................... ....392.................................. ...............................

....................................................................... ...............................

none

.............................. ................ E085 7B 2 spide,rweb.......................... . ....392......................................................................

.....................................................

none

........................................ E08 6 13A 4 ...... s,piderweb ........................................................................................................................................... 392

....................................................

none

................................... .......... E08 6 17C 5 §.piderweb .......................... 392 ........................................ ...............................

..I............................

no ne

............................................... E08 6 17C 8 spiderweb ..........:............... .392............ .

,

none

....................................... E08 6 17C 9 spiderweb ......................... 392.................................................................

....................................................

none

E08 6 176 12

Ti

..............................................spiderweb ......................... 392.................................. ...............................

.....................................................

none

............................................. E08 6 2C 16 spiderweb .......................... .392........ .................................................

.....................................................

n,one.....................

............................... E08 3 13C 16 ............... §.piderweb ..................... 360 ....... below ........................................... erosion ...............................

none

.............................................. E08 6 18A13 spiderweb ......................... ,360„ below............ erosion none

............................................... E08 4 iC 18 spiderweb„ 336................................ below BEDm....I........................ se Sims

E08 5 17A 9 ,,, ................................... .......s,piderweb ......................... 336................................................................. none

E08 5 

................................... 17D 9 .......... spiderweb ......................I.. 336....................................................................................................

.....................................................

sem

............................................... E08 5 7B 3 s p id e,rw.. b ......................... ,,,,.336 ................................................................

...............................

none , 

........ E085 7C 14 ...................................... sp,iderweb ............................................. 336 . .........................................................

......... ............................................

n,one..................... E08.................. 6 13A ......2.... ..........sP..iderweb ......................... .3.3.6......... .

...............................

none

E08 6 17C 10, , spiderwe,b 336

....................................................

none

summary of eHtended impacts H

as of 6/23/95

impact name type of impact size comments analusis to date

.................. E08 6 7A .................... 8 spiderweb ......................... 336. ...... ........... ................................... . .........A.................................. none

............................................. E086 7A 11 Sw....e,rwe.b .......................................... 336 ... . .........................................................

..................

none...................... ..........

.............................7............. E08 1 5A 7 spidery!!eb ......................... 300....... .

...............................

none

....................... E08 2 15B .... ................ .. 16 s.P..iderweb ............ ............. .300........

....................................................

none

................................. ............ E08 3 18D 25 spiderwe,b ......................... .....300.................................................................

............. .................................. .....

n,one .... ....................................................

............................................. E08 3 5C 12 spiderweb ......................... ,300........below.............................................................................. erosion none

............................................. E08 5 14B 14 S,piderweb .......................... 300..........below.............................................................................. erosion ...............................

none

.............................................. E081 2C 6 s.p...... SAAb ............................................. 280 . ..........................................................n,

...............................

one.....................

............................................. E08 1 9C 9 S,pide,rweb ......................... 2.8.0.........

...............................

none

.. ................................. E08 3 19A 2.......... s.P.. i derwe.b ......................... .......

280

....................................................

no

....... 4 V 1 ................................... spiderweb .......................... 280............ ..................

................................. ...............................

none

.EO8 4 15D .. 6 ......... spiderweb 280 .......below erosion

..................................................

none

................ E08 4 15D...........1 6....... spiderweb ......................... 280 ... ....... .

..................................................

n.one

.............................................. E08 4 3A 3 spide,rweb ..............................280..................... ...............................................

....................................................

none..................... .......... E08 5 18D 18 S,piderweb ,280 below erosion ...............................

none

............................................. E08 5 18D 20 spidgrweb ............................................. 280 . none

............................................. E08 5 19D 12 s.plderweb ......................... 280.. ........

....................................................

none

.............................................. E08 5 19D 14 s.P..iderweb......................... 2 8. .. 0..................................................

.......... ....................................................

none

.................................... E08 6 16C 15..........s,piderweb ......................... .....280.................................. ..I............................

....................................................

no e ..n......................... .............................

..................................................................................... E08 6 16D 11 s,piderweb ............................... 280 .

... ....

none

,E08 6 1,7B 12.. s.pide,rweb .....280 .........................................................

....................................................

none....................................................
7/2/95 4:35 PM 6/23/95.rev 15

summary of extended impacts p

as of 6/23/95

impact name type of impact size comments analusis to date

.............................................. E08 6 1 D 7 s p..ides w e b ........................................................................ 280 ............................... . none,,,,,,,,,,,,,,,,,,,,,

..................... E08 6 6 D...4...............S,pide,rweb ......................... 280...... s u e r.....by.....sPray .................

,,,,,,,,,,,,,,,,,,,,,,,,,,•....

none....................................................

.............................................. E08 6 7A 5 s.Pide,rweb .......................... ,,,,280....................................... ............................... !?,one...........

............................................... E086 7B 1 spide,rweb ..............................280....... . .........................................................

,,,,,,,,,,,,,,,•...............•.............

n,one.....................

.............................................. E08 6 86 1 spiderweb ......................... 250..............................

...............................

none

............................................... E08 1 3D 17 spiderweb .......................... 250....................................... ...............................

....................................................

none

................................... E08 2 12B 5 ..... spiderweb ...................... 250.................................. ...............................

...................

none ........................

......................... E08 2 12B.................. 13 spiderweb ......................... 250.............................. ...............................

. I ................ I..........

none

E08 2.....19A 12 ........................spiderweb .

,,,,240 none

............................................... E08 3 12C 19 spiderweb.......................... 240.................................. ............................... none....................

.............................................. E 08 3 13 B 17 s,p i d e r w e b... .................. 240....... ............ below erosion ............................ . ..

...............................

none

E08........1 A...9..... . s.P.. i d e,r w.. b ....................... ..240... a,ve,r I ...P.

.

.P....n.o.................... .....

....................................................

n,one....................................................

.................................................................................................... .............. erosion...................................:........................ ...............

........• ..................................... E08 3 5 B 1 s.p id e r w e b ......................... ,240..................................... ...................I...........

.. ......... ...............................

n,o n e

............................. EOS 3 5B 2.... .............spide,rweb ..............................240 . ............................................................I....

....................................................

non .....................

............................................... E08 3 5C 18 spiderweb ......................... 240...................................................................

...............................

none

............................................. E08 4 126 3 s,pide,rweb ......................... 240....................................... ............................I..

........................................................

none,,,,,,,,,,,,,,,,,,,,, E08 5 3C 23 ............................ .... spiderweb 240

,,,,,,,,,,,,,,,,,,•............

none

E08 6 13D 14 s,pide,rweb 240 none

E08 6 15A ,8 ... .....

.

spiderweb 240 ......................................... none 

E08„ 1 12A 6.... ...... .... spiderweb 224

............................... ........................................................

none

summary of extended impacts R

as of 6/23/95

impact name type of impact size comments analusis to date

E08 119D ....ix.................... 10 s,piderwe,b ......................... 224........................ .I........I.................... .......none

E08 1 9A2 ...... .......• ....... ...... spiderweb ........................................................................................................................................ 224

..................................................

none

............................................... E08 2 11C 5 spiderweb ...................................................................................................................................... 224

...............................

sem sims

............................................ E08 2 7B 5 . sp ide,rweb ........................................................................ 224 ...............................

.... ...............................

sem sims

.............................................. E08 3 10C 8 spiderweb ......................... 224....................................................................................................

.............

none

............................... E08 3 4C 1,4............ p i d.. rweb ......................... ,,,,,224..................................

...............................

n.°n e

.............................................. EO8 4 15 D 9 s,p i d e r w e b ...................... 224...............

...............................

below 

........................... erosion,,,,,,,,,,,,,,,,

............. ....................................................

,n.one.....................,,,,,,,,,,..,,,.....,.....,....

....... ........

ri n.o....too............................................ ..................... ................................... E08 4 15D . ....................... .... ......... ...

.

...... spiderweb ..............................224.. ........................ ........ ............................... n.^...e

.................................. ........... E08 5 11A 13 spiderweb ....I.................... 224.................................................................

...........................•....•...................

no....ne

................................................................. E08 5 17A 6 ......... spiderweb 224 .............................................. below erosion

..................................................

none

E08 5 17A 10 spiderweb 224

..................................................... ...............................

none,,,,,,,,,,,,,,,,,,,,,

....................................... E08 5 19B 4 ...... spiderweb ......................... 224....................................... ...............................

,,,,,,,,,,,,,,,,,,,,,,,,,,,•...

none

.............................................. E08 5 19D 4 spiderweb .......................... 224........below erosion

..........

none

E08 5 7B ..

................................. ............ ..sp de,rweb ............................................. 224

.................................................................

................................I......................... n,one

..

.......................................

...•..• ............ 7C E085 .......................... 9 ..s piderweb ............................................. 224 ........................... ...............................

....................................................

none..................... E08 5 7C 13 ...................................spiderweb......................... ,224....... . below............................I........... ..... erosion

...............................

none

.............5... 9 E085 .......................... D 5 spiderweb ......................... .....224....... . ..........................

...............I................................................

n,one.....................

..•• .......................................... E08 5 9D 10 spiderweb ......................... 224.......

...............................

below..........rosio en..................................

............................... Wan e

......• ........................................ E086 7.. 4 spiderweb ......................... 224....... . ..........................

...•............................................................

n,one...................................................... E08 6 7C 5 spiderweb ,,,,,224

...............................

none
7/2/95 4:35 PM 6/23/95.rev 16

summary of extended impacts H

as of 6/23/95

impact name type of impact size comments analysis to date

.................................. E081 5D 29..... ...... ..spiderweb.......................... ....1.8......... 0 .......................................................... non,e ....................................... I ........ ....

E08 5 56 3.................spiderweb .......................... 180..........below........................................................................,..... erosion none ...............................

E08 4 1 86. . ........ .. ..........s.P.... . . .....

i de rweb ...................... ..1.75................................... ........................ .....n,one.................................................. ..

............................................. E08 5 17A 15 spide,rweb ..............................1.70...... faint,. .....below..............,....... n,one....................................................

....................................................................... ............................................... erosion....................,.............. .................................... ............ ...............................

.E08.„ 1 .... 19D ..„11........

, spiderweb. ...................... . ..... ,1.68....., .. ....none.....,............................................ ..

................................... E08 4 19A 5 ..... s p i.. e r w.. b....................,.......... ,,,, 1, 68 .. .......................................................... non e. ...,.........

.......................................

......................... E08 4 19C 15 .................spiderweb.......................... I......... ,168 below........................................... erosion ............................................ , ................... .. none

......................... E08 5 11A 15 ............ ... s,piderweb ..........:.............. . 1.68 ................................................................ none ....................................................

.............................................. E08 5 iD apiderweb .......................................................................................................................................... 168 none ...............................

......................... E08 6 16C 13 .................spiderweb .......................... 1.68..................................... ............................... n,one

.............................................. E086 8A 1 spiderweb.....,.................... 1.68....... . at....edge ..................................... n,one....................................................

.............................................. E08 5 19D 2 spiderweb .......................... 160.................................. ............................... none........................................................

............................................. E08 5 12A 3 spiderweb . .......................................................................................................................................... 140 none ...............................

...................... E08 4 7A......1.1...........s.P.,.iderweb........................ . . 120...............................,,. .....0......................... none .................................................... 

................................. .. E08 6 1.......... s.P,. i de r web . .............................1.20...... sP.....extends.....720.^.......... n,on e ....................................................

....................................... ........................................................................°. u. t......................................,...... ..... .. E08 5 18D 7 spiderweb ..................0...... 1.1,2....,............................, .........0..................... none .....................................................

.............................................. E08 1 3D 18 sp,ide,rweb ... 400 maybe lust none. .......................................................

................... scratches

summary of extended impacts !t

as of 6/23/95

impact name type of impact size comments analusis to date

..................... E08 2 1B 3.....................spray 5600 out from ...... ............edoe ....................................... none

.......................................... E03 1 15A 1 C„ spray 2 4 0 0 .............................................................................................. not so dense

...............................

Reim

.............................................. E08 2 18B 2 sp r,a,y.................. 1680...........................................................................,,....,.......,...,........ more extends down

...............................

none

................ E08 2 16A......3 ......... s.P,JAY.............................................1568 .................................... ...............................

............

sem sim

..........I........

....... s........

.............................6.............. E08 4 1A 6 spy.ay . ............................................. 1 512.............................. ...............................

...... ...............................

none.....................

........................................... CO2 2 12A 1 C„ sp, r,a,y ..................................... ...1,200 ........................................ ...............................

...............................

sem......................... Sims

E03459A ...................5..................................... s.PJAY........................................................... 1 ...................I...........

...............................

sem Sims..,..... ....

................................... E08 2 6B 1............ s P.^.a.Y............................................ 1200 .,..................................... ...............................

...............................

none ......................

............................................. E08 4 20811 sP,ray ................. 1200,,, very Misible ........................................................

...............................

sem

.............................................. E08 2 9B 4 s.P,.r.aY ............................................1120................................. ...............................

...............................

none ......................

.............................................. E08 6 6C 4 s.P.^.a,Y.............................................1064 ....................................... ...............................

...............................

,none

................................. E08 2 6 12,......... . P.,r.a.Y............................................900.......

....... .........................................,..........

none

.............................................. E08 4 7C 3 spray,,,,,,,,,,,,,,,,,, .900 ..............

in semicircle ..................................................................

...................................................

sem

............................................. EO8 5 3C16 spr,a,y..................

................. 900.......

Iona, ,and ,narrow ..............................................................

...............................

none

.............................................. E085 9D 9 s.P..^.a.Y.........................: .............. ....896....... ..........................................................

...............................

none.....................

.......... .... ................ E08 2 20A ... ...... 12 .......s.P..P.AY ...........................................840....... . .........................................................

...............................

none......................

..................... E08 6 8C 

..................... 2 s.P,r.a,Y ...........................................540 ............ .

...............................

none

........................................... E03 4 75D 1 C.. s.P..r,aY .......................................8...^.0..........

....................................................

sem Sims

E03 4 77A T. .............................................. s.P...a.Y....................................... .................... 800 ............................................

.............,...,,,...........................................

sem sims

..................... E083 7iJ 2.................... s. PJAY............................................784.......................................................:. .............

...............................................................

none....................................................
7/2/95 4:35 PM 6/23/95.rev 17

summary of extended impacts R

as of 6/23/95

impact name type of impact size comments analusis to date

..E08 . .......... . . ....4 .... 14.. ..D.................. 8 . sP,raY ......................................

.

.7,8,4 ........ . v,isib,le,,,,,,,di discolor. ...none

........,,. ...... .... ......

none ......................... ...................................

w.....n. .....e..... ith nakd .... ...eYA ................................................. ...............................

E08...6 17C 7.. . $.P..r,aY ................................. I.. 784 ..

....... ............................. none.........

..................... E08 6 6l) 3.................... s,RKAY....................................... .....7............. 28 criike........damage.,.,,,,,,,,,,,,,,,

....

.................................................................. none

.............. incente.......,............................................................................................

......................... E082 15 D 2.................

.s ....................................................

...p.r.a.Y............................................672.......... . .......................... n,one...,,,..............................................

......................... E08 2 17A 3 ................ s,P,r,a.Y........................................6.7.?.,,......

...........I...................

sem sims........

....................... E08 3 11A 14 ................ s.P..r.aY ...........................................672 ......................................

,........,... ...............................

none

............................................. E083 11 A 18 s.P.r.a.Y.........................: .............. ....672.......

...............................

................... ......................................

...................................................

n.................... one.

E08...3 ......... 20D 16 ................ s. P.,r.a.Y............................................672...... is...... around crater ........ .............................. .

. ...............................

n.one.....................

..................... E08 6 6C..................... 8 s,P,ra,Y................. 672...............extensive. in .a .................................................

...............................

none ...............................

....................................... ...................................................... sunburst

................................................ ...................................

............................................. ...................................................... ................... .

form foration ......................(tKp.M...........

...............................

.

.................................... ..................................................... . .................... ed.e..........ot.................................. ...................................

............ I....... individual spraXs

...............................

..................................................................

... .. ..... .. .. .................... may....be....ihe re

but ........ ..... ..

............I .......................... ............................................................. .................... difficult

...................................

to teii ............

............................................. ....................................................... .................... because,.......

....... ,..........................................................

of.,.,.........................................................................................

....................................... erosion..... rosion in the.................................................... ...............................

............................ ................................................. ............................... a,

 r e a.:.............................,................................................

E0.... ............................ 6 8A 2 s.P.r.a.Y.............I...................... 672

...............................

n,one....................................................

summary of extended impacts H

as of 6/23/95

impact name type of impact size comments analusis to date

E03 1 15B 2 ............... .............. C.. s.P.r.a.Y........................................6.....,,..,. ...... 4 0 close to the ed9.e......... s.err!...................... E08 6 6D 8 s.P..r,a.Y............................................616

...... ....................

cr. .. .... Inin .... . center ........... .E .... AP ...0..... sp

...............................

n,one....................................................

................................................. ............................... s. U. !. r.................,..............................................................

.............................................. E082 10B15 s.P.JAY............................................600......... .

...I...........................

n,one....................................................

...................... E083 6C...1.1............§.P..r,a.Y............................................600....... ............................ none..................... E08 5 14B 7..... s.P.r.a.Y............................................600 .......

...............................

strange.....shaP..e................. none 

...............................

.e .................................................. E08 6 20C ......................... ................ 19 .s.P..ra,Y.............0..............................600...................................... none

............................................. E08 .. 20D 25 s,P,r,aY ...................................... .....600,,,,,,

...........................

.000d.....ce nter

.....................................................

none

....................................... E08 114B 10 ...... s PJAY ......... 560............

.............................................................. ...............................

none

.............................................. E08 2 17C 16 s.P..r.a.Y........................................5.6.0......... hit

.......

t he.......very.......................

....................................................

s.em..........,............

................................... ................................................................ .................... edge,;.... there.... is..................... a

...............................

.

....................................... ................................................................................. debris trail ........................................ that........., ...................................

.............................................. ............. ........................................ .........0.......... extends........... for.......................

...............................

..................

..... ...................... ..................................................... another ............................. 1960 ............ !?n?..........

................................................

.................................. E08 3 11A .. s.P,r.aY ...........................................560 .................................

...............................

none

. E08 3 ......... .... .. .... ...... .... .... ..... 19D 9 .......s.P..r.a.X .................. .......................0..........

................................

. ..........................

.........................................................

n,one.....................

............................. .......... E083 7C 11 ..... . s.P.r.aY . .............................. ............560............

............................... ...............................

n,one.....................

....................................... E084 16C 10 ...... .sP..r.a.Y ..........................................56 . .. .,,,........ 0 

...........................

.........................,.....

none,.................... E085 11A 10 sRKAY ...........................................560............

...............................

w/... 1.^.OkL......crate.r.............none

...............................

E08 5 19D 9 s P......,.X ................. ra ......................... .

. 560 ..... . ........

........................................................

non e

E086 13B 5 s.P.r.a.Y................................a...... 5 6 0

.............................................................................................

..........................................................

...............................

n,o n e ..........................................
7/2/95 4:35 PM 6/23/95.rev 18

summary of eutended impacts ii

as of 6/23/95

impact name type of impact size comments analysis to data

..................... E08 6 5D 8.....................sp,r,ay . 560....... .......................................................... .................................................................. sem Sims

.......................................... E03 3 62 C 4 s.P.r.a.Y........................................5,5,0........................................................................................... none ..........................................

.............................................. E08 5 16B 19 s,p,ray ....... 540.................................................................................................... below erosion sem ...............................

......................... E08 1 12B................ 12 s.P.r.a.Y........................................ ................................................................................................................ 504 non e ...............................

.............................................. E08 2 18C 23 spray . ..... . . 504.................................................................................................... none ...............................

..................................11 E08 3 11A 11 ........sp.r.a.Y.......................... ................. ..................................... ...............................none o...........................................................

......................... E08 511 . 6..................s p, r,a,Y...............I.......... .............

,,,,5 04.................................................................................................... none ...............................

E08 6 

TiT.

..................... .....................sp, AY...........I ......... ...... ...................................................................................................................... 504 below erosion none ...............................

.......................................... E08 6 7C 9 spray ................ 504..........crater-like ........................................... none ..........................................................

.......... ....... . ............. . ........................ ............................. center ............................ . .............. . ............ .. ..... . ............. . .............. ................................

................ ... . ...... ................... E03 238C 5 ..spray ........5,0 0...................................................................................................... sem sims ...............................

E084 7D 7 ... s.P..r.a.Y ............................. .......... .500....... ................ ................................................ none

.... . ............................. ..........................

..................... ........I........

...E03 4 75B 1 .....C.. s.P.r.a.Y.......... ..............................4 8 0...... ........... dense. .e, .....................................

like a ... . ...e m............. ........ .................................

......................................................... ............................... r i.o.g................................................................................ ...............................

E08 4 26 9 ........... .... ......... .... ....4...........s,p,r,ay .................. .................... ,,,,480 good center none ...................... ...I...........................

...................... E08 4 2C 14 ..... .............s .,r.ay ...........................................480 ............

...................................o......

. non? .....................................................

.. ...... E08 5 2D 

..... 6..............1.3...........s.P. MAY............................................480........................................................................ . none. .......................................................

............................................. E086 19D 8 . s. P..r.a.Y............................................480...... fainter....

..

.sp.............................. n,one....................................................

........................................................................................................................... extends ............................... . E08 3 11 B ............ .......... 10 ..... s. P.r.a.Y............................................448................................................................... ................................................................. non e . E08 4 14B 9 s.P.r.a.Y........................................448 none

summary of eutended impacts R

as of 6/23/95

impact name type of impact size comments analysis to date

.......................................... E08 6 6B5 a p.r.Ay ..........................................448.................................................................................................... no.ne ...............................

E08 6 8A 5 s.P.r.a.Y.. ...... I ...................................448 none

................................... E08 6 7B 10...........s.P.r.a.Y........................... ............. 440........................................................................... non e. .......................................................

...... E08 2 15B 1 ............... .................. 15 sP..r.a.Y............................................420.................................................................................................... none ...............................

........................................... E082 19A 5 .. s.RKAY ...........................................420................................................................. ............. non e.....................................................

.............................................. E08 2 6D 23 s p.r.a.Y............................................420.............................................................................. non e.....................................................

...................... E085 11 C . 21 . s P..r.ay ...........................................420............................... ....................................................................... non e ...............................

E08 5 2D 1 4" ............................... .4...........U.r.A.Y............................................420.................................................................................................... none ...............................

..................... E08 6 9C 3.................... sP, Ay ..................... ................,,,,4 20.................................................................................... none ...............................

.......................................................................................... E03 1 30B 2 s.P..K.a.Y........................................400 has a tai lI..............................

i................

s s .................................... ..............................

............................................................. ...........................18 0 0 u m)..................................................................... ...............................

E08 1 4A 19 ap.r.a.Y.. .... I .....................................400 none

.................... .................. . E08 1 12B 8 .......s.RKAY ...........................................392 ........exteR...M9......f ............. rom. . none.....................................................

.......... .............. ....e d 9 e............................................ .................................................................

............... E08 1....2C..................... 9 s.P.r.a.Y......................... .............. .... 392...... (a r se.....b rown. ...................... n,one....................................................

...................................... ....... ....................................................... .................... ................ disc o...... lo rati .............. o...n ...................................................... ...............................

...................................................................................................................................................................................................................... erosion? ...............................

.............................................. E0 8 1 2C 13 UIAY,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, ,,,,,3 92........brown .... .....I......................... E D in ri n g,,,,,,,,, .................................................................. non e

............................................. E08 1 5A 11 s.p.r.a.Y............................................392..................... has some debris ............................... n,one....................................................

..................................................................................................................................................................................................................... below ...............................

E08 2

8 .... 10

sP.r.a.Y............................................392 none
7/2/95 4:35 PM 6/23/95.rev 19

summary of eHtended impacts H

as of 6/23/95

impact name type of impact size comments analysis to date

E08 3 10C 17 ..... .................s. P.ra.Y......39 ...................................... 2 ................................. .............I................, n,one....................................................

E084 18D 3 sRLAY ...........................................392 ......................................................... none.....................

.............................................. E08 6 16C 11 s•pr,ay......,•„ ..............................392........overlaps ,erosion .... D.............................................

...............................

none

E086 176 6..... s.P.r.a.Y................................. ....3 92

...............................

none.....................

.............................................. E08 617C 13 s.P..r.a.Y....................................... ................................................................................................................. 392

...............................

non e

..................... E08 6 1,B 2.....................s. P.r.aY ...........................................392....... ... .......................................................

...............................

none

.............................................. E08 6 6D 10 ...A..rM ..........................................392.................................. ...............................

................................ .....................

none

.............................................. E086 6D 12 s. P.r.a.Y............................................392........belo............ eriI........... r....................

.....................................................

n.one

..................... E08 6 8D 

.................... 3 s.P.r.a.Y.......................... ..................32................................... 9 ...............................

............................................ ,........

n.one.....................

..................... E032 ...................... ........................................3.6.0......... . .........................................................

...............................

ix none.....................

.............................................. E08 3 3A 6 §.P..r.a.Y ...........................................360..........below.............. erosio.^.................

...............................

n,one....................................................

..................................................................... ............................... .................... e.n..e ........................ . ............... p

............................................. E086 10B 1 s.P.r.a.X ...................................... .... 3.60 ........................................... ...............................

....o...........................................................

n,one

............................................... E08 1 13D 14 sP..r.a.Y.............................I......... .................................................. 336 ...............................

....................................................

none

............................................... E08 1 15A 18 sP..r.aY .......................................336....I.......overlies bl. ..............................................

.................... .......................................

n,one....................................................

..................................................................... ............................... ........ I........... e ili.P..t:.......disc :........................

............................................... E08 1 15B 2 s P..r.a.Y.......................................

. 3 3 6 .......................... ...... ................

.................. ................................................

n,one..................... E081 5A.......1 ................................. ..........s.P.r.ay .......................................... 9 .336

r.............

su... .........by................

........................ .......

n.one....................................................

........................................................... ....................................... .. ........... . ..... bro RE

E08 2 8D 12 ............... .......................s.P.r.a.Y............................................. 336.......................................

..................................

...............................

.................. ................. ...............................

non e

..... ...... .............. 3 ......... 1 1A . s.P..r.a.Y............................................336 ........................................I..............

.............. ......................................... I..........

none...........

summary of entended impacts H

as of 6/23/95

impact name type of impact size comments analysis to date

............................................... E08 4 10A 9 s P..r.e.Y....................................... 336 ............ n.on.e.................

.............................................. E08 4 11 A 3 s.P..!'.a.Y.......................................

........i ....I...

...................................... 3 3 6

...............................

...............................

....................................

n,o n e

................................. E084 11 D 1............ s.P..r.a.Y....................................... ........... 3 3 6 .........

.........

.................. ........................................n,

.....................................................

one.....................

.............................................. E08 4 11 D 8 s.P..r.a.X ...................................... ..................... 3 3 6

...............................

non es.

............................................. E08 4 15A 3 s.P.. r a.X ...................................... ........................ 336

....... ....................

none

............................................. E08 4 19C 6 s. P..r.aY ...........................................336........overlaps.....ri.....and............. .....

.....................................................

n•on .....................................................

................................ ..................................................................... .................. e ............... rosion

...................... E08 4 5A 

................... 18 s.RUY ...........................................336..................................

....................................

...............................

..................................................................

non e

............................................ E08 5 11 A 19 s.RDAY......................................... ...336..................................

...................................................

non e

.......................................... E08 5 12A 6 .s. P..r.a.Y............................................336........

..........................I.... .............................................................

non e

....................................... E08 5 17A 12 ...... spr•a••Y.........,••„•••.•.•.• .336............below erosion

.............................................................

non.e

.............................................. E086 17B 2 s.P. AY ...........................................336 .............

.............................................................................

.........................................................

...............................

non e

............................................. E08 6 2C 18 s.P.r.a.Y............................................336........................................ ...............................

.......... .....................................................

non e

.............................................. E086 5A 5 s. P.C.a.Y ...........................................336..................................... ...............................

...............................................................

none....................

.......................................... E086 5A 7 s.P..r.a.Y........................ ................ 336...........................................

...............................

n•one.....................

.............................................. E08 6 7B 6 s,p, r•a .....................••_...•..•••.••• ••,.,336......... ................................................................................................

... ......

c r a ter - i i k e non e

......... ...............................

...............................

......................................................... ............................... center....................... .............

............................................ E086 7C 8 .s.A..r.aY ...........................................336 .............

........................................................... ........ ............

non.e.....................

............................................. E03 2 12D 1 sp.ray ...........................•.•.•.... 300..........stranoe:shaped......•....•

.... ...............................

................................... sem

......................................................................................... ............................... dens e

...............................
7/2/95 4:35 PM 6/23/95.rev 20

summary of entended impacts R

as of 6/23/95

impact name type of impact size comments analysis to date

.............. E08 3 13C 5 ............................... sP,raY ................. 300.............below......................................................................... eroosion none ....................................

......................... E083 18D 23 .................s.p.r.a.Y ........................... .................300............ . n,one.....................

.............................................. E08 3 58 6 spray ..... 300.................................................................................................... below erosion

...............................

none ...............................

..................................................................... ............................... . ............... e..!.PS.e............................................ ... ...........................................................

.............. E083 6C 13 ............................... s.P..aY ...........................................300.......... . none....................................................

E085 13C 18 s.P.r.aY ...........................................300...... s tra p.Pe..... ..... 1 .... .. ......... ................ shaP..e .................. none

.........................

.E08 5 16 C................ 10 s.PJAY ............... ............................300.......... ..... ......................................................

....................................................

none.....................

.. ........ .... E085 

.... 6............... s.P..r.a.Y............................................30.0 ..... . .......................... .........................I.....

...............................

n.one.....................

.............................................. E08 5 i-6 16 s.P. MAY........................:. .............. .300................................

...............................

none ....................................................

.............................................. EOS5 3C 15 s.P.. .a.Y....................................... ............................... 300 .......... none 

. .....................

............................................. E085 8C 11 . s.P..r.a.Y............................................300................................. ...............................

...............................

n,one .........................................

...... E08 6 15A 20 1............... ................ s.P.r.a.Y....................................... .. .0..................................... ...............................

...........

n,one.....................

............................................. E08 6 20A 17 sP,r,aY 300..........below............................................................................... erosion

...............................

none ...............................

................................... E08 6 20B 5.......... s.P.r.aY ...........................................300.............below..... erosion................. n,one.....................

................................. E086 5C 5 .............

.....

sp.r.a.Y.. .................. . ....................... 300 ........... ...........................................................

...........................

none ... ....................................................

E08 3 19A 3 ,,,

................................... ......sp ray 296 ................almost crater ........................................................................... none ...............................

............................................................................................... ........................l!. k e...............................................................................

I.n.o.n.e

.............................................. E08 1 14A 11 s P..r.a.Y............................................280 ....................................... ...............................

............................... ..

,n,o n e .....................................................

EO$ 1 i

.

........................................ 0 16 S. P.r.a.Y........................................2.80 . . ...................................................

E08 1.............1 C 21 ...... ..... ..... s.P..r.aY .................. .......................

6........

?.8 o........... non ................ e

......................................... 1 i 23 s.P.. r.a.Y........................................2.8.0 n.°n e

summary of eHtended impacts H

as of 6/23/95

impact name type of impact size comments analusis t o date

.............................................. E081 2C 12 s.P..r.a.Y............................................280. ...... . ......................................................... n,one.....................

. ............................................ E081 2C 14 .. s P..r.a.Y.. ...................................... ................... 280 . .........................................................

...............................

n,one....................................................

...................... E081. 2C 15 ..... ............s.p.r.a.X ...........................................280.. ....... . none

E08 1 ..B 14 sP,ra,Y..................................... ..280 .....................debris fans out

.................................................................................

.....................................................

none ...............................

............................... ......... .............................. .............................. .................. .

for.......280....k?m............................................................ ...............................

E08 2

16A ...... ........................ ......s.P..r.a.Y............................................280 ............ . none.....................

.......................... .................... E082 3A 2 s.P. AY............................................280...................................................................

.......................... .....

non......................... e

............................................... E082 9 B 11 s.P..F a.Y............................................280 ............ .

...............................

n,one.....................

E08 3 10C 14 s.A...a.Y....................................... 280 ................................... ............................... - .

...............................

none

E08 3 10D 1 ..............................................sP.r.a.Y............................................280. .........

.............................................

none

............................................. E083 1 A 1 s.PJAY ...........................................280.................................................................

.....................................I...............

non e

................. E08 3 .................. TWA .......s P..r.aY ...........................................280 ....... . .........................................................

.........................................................

n,one.....................

.............................................. E08 4 10A 3 s.P.r.aY ...........................................280.................................. below BED...............................

...............................

n,one.....................

............................................. E08415A 13 s. P.r.a.Y............................................280....... .

...............................

n,one.....................

.E08...4 .„ 1 ...

.. i..! .........s.P..r.aY .................................... ..... ..2 80 ........below.....erosion.............. ....

...............................

n.one...................

............................. E08 4 3D 8................ s.PS aY ...........................................280....... . ........................................

............................... ..

none.....................

................................... E08 5 11A 2 ......s, P, ra,Y................. .280..........below. ..... ..................................................................... erosion

...............................

none

................................... E085 12A 4 ......... s.P.r.a.Y............................................280 ............

...............................

n,one.....................

.............................................. E08519A 6 s.P.r.a.Y............................................280.......... . .........................................................

...............................

none.....................

,E08 5 19C 5 s.P..rAY........ ..2 80

...............................

none.......
7/2/95 4:35 PM 6/23/95.rev 21

summary of eHtended impacts R

as of 5/23/95

impact name type of impact size comments analysis to date

.............................................. E085 8D 2 s.P. A.Y............................................280....... .below ............. . erosion................. n,one....................................................

................................... E08 5 9B 17...........s.P..r.a.Y............................................280....... overlaPS......erosion......... sera sims.......................................

EO8 5 9D 2 AR KAY ....................... 280 below erosion none

........................ E08 6 16 D ................... 3 s P..r.aY ............... ............................280...................................................................................................... non e ...............................

......................... E08 6 17A 5................... ..........................................280 . ................................................................................................... . non e ...............................

E08 6 8C 6 ...RU.Y............................................280 none

E08 5 12D .. ...................... .......... 1 ....... .... .... SP..r.a.Y..252 .......................................... . ................................................................ . n............ one .....................................................

................................r.a.Y E08 1 3D.... . 16 .......... . sP. ....250 ....................................... .... ................................................................ . n................................................................. one

......................... E08 2 12B 3.................s.P. MAY.....................:......................250.................................................................................................... none ...............................

............................................... E08 2 6C 16 sP..r.a.Y............................................240.................................................................................................... none ...............................

.................................... E08 3 i D 19.......... § .P...aY ...................................... .....240................................................................ .n,one....................................................

............................................... E083 3D 5 .. P..r.a.Y........................... .................240 ................................................................ n,one..................... .........I.....................

.............................................. E08 3 5B 5 sPra,Y........................... 240....... below.............................................................................. erosion none ...............................

................ ............. ................ ................................................. I .... . .................... e.UP.a!e....................................... .................................................................. .

.............................................. E08 3 56 7 ARK

.......

....... ..........................I.... ,,,,_240....... below erosion : ............. ....... .....................................................I.,.......... none

.....................................................................................................................................................................................................................

faint

...............................

............................................... E08 3 56 9 s P.r.a.Y ...........................................240................................................................. ...... none ....................... ............................ .........

................................... E083 5 B 17...........s .P..r.a.Y................................................................. . ............................ ... n,one....................................................

........................................ E08 3 6B 15 s.P..r.ay .................. ........................240.................................................................................................... one ...............................

E08................. 5 13 C...6................s.P..K.aY ..................240 ......................... ..........below.........................I................. erosion n,..one.....................................................

summary of eHtended impacts R

as of 5/23/95

impact name type of impact size comments analysis to date

.............................................. E08 5 13C17 s.P..r.aY.......................... .............. 240....... strange.....shaP.e.................. none....................................................

.............................................. E08 6 106 2 s.P..r.a.Y............................................240.................................................................................................... non e ...............................

............................................... E0.. 6 10D 16 sPIAY ...........................................240....... . none ....................................................

...................... E08 6 14C 9 .......................................... .. s. P...U.Y................... ............................... 240........ faint ....................... &below. ........................ none ...............................

.................................................................................................................................................. errosion ................................................................... ...............................

................................... E081 5A 15...........s. P.r.aY ...........................................235.................................. ............................... n.one....................................................

............................................... E08 1 12A 18 spray .......... 224....................................................................................................... none ...............................

................ E08 1 12C................... 11 sP,r,a,Y................. 224..........BED................. below. ................................................................ SP none ...............................

.............................................. E081 4C 35 s.P..r.a.Y............................................224.................................. ............................... n_one ........... ..........................................

............................................... E081 66 1 s P.!:.a.Y....................................... ?,2,4.................................... ............................... . n,one..................................................:.

E08 2 1.. 5.... s P.r.a.Y ...........................................224 none ....................................................

.............................................. E08 2 16A 10 sPJAY ................ 224..........extends.........

towards ......................................................... none ...............................

.................................... corner.......#4 ............................................. ...............................

.................................. E08 2 18C ...... 11 .......sP.r.aY.......................... ..................224........overlaps.....BED.................... ... none ....................................................

....................................... E082 18 D11 ...... s.P..!:.a.Y............................................224.................................. ............................... n,one....................................................

............................................... E0823A 1 sP.r.aY ...........................................224....................................................................n,one....................................................

.............................................. E082 8D 13 sP..r.a. . Y............................................224................................................................ none....................................................

...................... E083 11 B.........2............s P.r.a.Y............................................224................................... ............................... n,one..................... ...............................

.............................................. E08 3 19C 13 s.P..r.a.Y............................................224. ....I..ov„erjaip ...BED.................... ................................... none ...............................

,E08 ....................................s 3 4A 2 s.P..r.aY ............................... ....... . ....224.................................... .............................n.one....................................................

,E08 4 10A 10 s P.r.aY ...........................................224 none
7/2/95 4:35 PM 6/23/95.rev 22

summary of eHtended impacts fi

as of 6/23/95

impact name type of impact size comments analysis to dote

E08 4 10A 19 ...........................................224 224 ......................................................................................... non e ..........•....................

.E08 4 ... ... 1,O ............ 22 S.P.KaY.................................... .......224.., .....below....BED.......................... ....none•.................................................. ..

.............................. ..... E08 4 11 B 3 ..... ......s .P•.r.a.Y .......................................2.2.4...................................... .............................n, one....................................................

................. ........ E084 14D......11...........s.p.r.a.Y• . ..................................... . ........ ............................................•............. none.................................................... ..

E08 ..4................... 15A 6.... ...... .s .P.r.aY ................................ .....................•................................................................................................. 224 none ...............................

.............................................. E085 12D 8 s P.r.aY ........................................... . 224.................................. ...•........................... none.....•..................................,...........

E08 5 6C 8 sera,Y..................................... 224 sem sims

...................... E08 5 7C 6....................s. P•reY ...........................................224 ..••• ...,.......below.......,,•.. .. erosio.n................. n,on...................,................................. e

................................... E086 13B ............ . s.P.r,aY ....... ................................ 2.2.4........ ......................... ........... ....•................. Aone..• .................................................

E08 6 1 A 8........ ...... ..... .s MAY ........................................... . 224................................. ............................... n,one .....................................................

.................................••,........... E08 4 1 8 2 s PJAY ...........................................220....................................................................................................

.. o n e ...............................

E08 4 7A 10,,,,

...................... ......

,

......AR LAY...........................................210.............below.............................................................................. arosion none ...............................

.............................................. E084 7C 11 s.P•,r.aY.........................................•.,21,0.,............................................................................ non e .....................................................

........................................ E08 5 5B 1 S.P,r•a.Y............................ ........... 210 ......... . below..... erosio.n................. n,one....................................................

.............................................. E083 4C 16 sP•. . r.a.Y............................................ 1.96...............,................................................. n•on.e....................................................

.......................•.........•............ E08 4 15A 10 s. P•.r•aY• .................. ..................... ....1.96...... below........................................... erosion none....................................................

E03 2 28A .....4 ..........s.P..r.a.Y........................................1..8.0, ....... •verv....dens e......... 

spray...•.... non e........................................................

............................................... E082 19A 13 sP•r•aY ...................................... .... 1 . ...80............................................. .........................one.. ...... n.................................................

E083 6B 4 "'KAY............................................1.80 none.....................................................

......................................

 4 6 2sP.r•a•Y•.........•................................1,80• ... dark .......... 7.. ..below ...........a.. .................... none •...•••••..••

.....

Ierosion ..................................................................

summary of entended impacts H

as of 6/23/95

impact name type of impact size comments analysis to date

E08 5 .....•• ...................... 5B 15 sp,r,a,g ................. 180............below........................................... erosion ....................................... I.......................... none

.............................................. E08 6 19D 15 sp r, aY ....................................

...................... 180 .below............................................................................... erosion none

E08 6 20C 18 s.P..!:.aY ...........................................180 ........................................ .........I.....................

...............................

none ........................................

E08 1 ....12B •...•.........5..... s.P.r.aY ...........................................1,68 ................................. .................•............. none .....................................................

.............................................. E08 2 13 D 13 s.P..r.a.Y............................................168 ........................................... ...............................none ......................

.................................... E08 2 17C 9.......... s.P..r.a.Y• ...................................... ............................................... 1 68 ...............................

...............................

none ........................................

..•....• ................. E082 17D 10 .......... s.P..r.a Y . ..................................... .1..6.8

....................................................................... s e mm

...................................... ....... E08 3 10 D 18 s.P•.r.aY ...........................................1.68.

.......

...................................... .............................

..........................................

n,one......................

E08 3 15B 18 s,P.r.a.Y..............••.............•...•.... 1 6 8..................................... ...............................

...............................

non e

............................................ E08 3 15 22 s.P..r.a.Y........................................1..6.8.................................... also a number...of.........,

.....................................I...............

n,one.....................................:......:....:..

......................................................................................... ............................... c rate.. .......

rs.........in ..... the ....

......................................................................................... ............................... area.....'..........................................................................................................

..................................................................... ............................... ....................i n t e r eSt.i.n.B i.......................................................... ...............................

............................................. E083 4A 1 s.P•.r.aY ...........................................1,68..................................... ............................... Anone

............................................. E084 10A 4 s.P..a.Y.........................:. ............. 1.68...................................................... .............

................................................

. non.e....................................................

................................... E08 4 14A 3.......... S.RKAY..........................................6.8.................................... ............................... none..................... ............................... E08 4 15A 4 .... s.P.r.a.Y• ........................... ...........................................1:68........ none

.............................................. E08 4 15D 11 sp,r,a,Y..........................................168

..............

below erosion

........................................................

none

............................................. E08 4 3A 2 s,P..r,aY ...........................................1.68

......................................................................................................

..................................... ...............................

...............................

non e

..................... E084 4C 3.................... s.P•.r.a.Y........................................1..6............. 8 ...........................................................non

...............................................................

e ...............................................................
7/2/95 4:35 PM 6/23/95.rev 23

summary of extended impacts IR

as of 6/23/95

impact name type of impact size comments analysis to da te

................................ E08 4 5A 5...............$P..L.aY ...........................................168 ... ... ... . .... ........ ............. below BED................................n,one ....................................................

E08 4 5 1 ....................... ........sPSAY ...........................................1,68.................................................................................................... none ...............................

............................................... E08 5 12D12 sP..^.a.Y................................... .... 1,68.................................................................................................... none ...............................

................................... E085 17B 8...........s.P..L.aY ...........................................168 ....................................................................... e. ........................................ ............ non

......................... E08 5 18D 14 ..................§P..r.a.Y............................................1,68.................................................................................................... none ...............................

.............................................. E08 5 6C 10 s.P..r.a.Y ......................................1..6,8 .. ..........blue ... .........elli.lit:................ .......... ............ se m ......................................................

............................................. . .................................................................... d! s c o.i.o! :.................................................................. ..I............................

.............................................. E08 5 8B 1 s.P.. A.Y............................................168 ........................................................................................................ none ....................I..........

. ..................... E086 17C 14 ..................sP..L.aY ........................... ............ 168 ... ................................................................. none ....................................................

............................................... E086 1A 6 sp.r.a.Y............................................1,68.................................. ............................... .none....................................................

............................................... E08 6 6A 1 sP..L.a.Y ...........................................168............................................................................... none ....................................................

E08 6 7C 2..................sP..r.aY ...........................................1,68.................................................................................................... no ...............................

.............................................. E08 4 6B 2 s.P..r.aY .................... .................... ...150 ... ..........below below......erosion................. n.one....................................................

. ....... .......... .... .............................................. ............................... ................... el,lip,Se......................................................................... ...............................

. E08 4 9B 1 .................... .....................s. P..L.aY ...........................................140 .................................................. ............................... nonee....................................................

............................................... E 6 1 A 1 s P..L.a.Y............................................1.40....... . ..................... ............. . ...................... .n,one.................................................... 1

...................... E08 1 5A......... 13.... 0.......sP..L.a.Y............................................1,30..................................0.............................. none.............I ....... I......... .........................

..............................a................ E08 3 18D 17 sP.L.a.Y ...........................................120....................... or bottom of ... ............................... none....................................................

............................................................... ............................... r i.o.o I.?......................................................................... ...............................

.E08 5 5D 20 ............ ........ .... ..... .SP..L.a.Y.. ..........................................120....... .......................................................... none....................................................

,E08 4 16D 1 9.. s.P..L.aY............................................1.1,2 none ........................

summary of ex tended impac ts H

as of 6/23/95

impact name type of impact size commen ts

analysis to date

................................... E084 19A .............sP.K.a.Y............................................1.1.?....... . n,one....................................................

.............................................. E084 5B 3 s. P..L.aY ...........................................1,12........................................ ............................... none.........................

..... E08 5 10B .2 ... . .. ..........s. . P..L.aY.................................... .. ..... 1.1 ....... .......

.............................. .

sem....sins..................................... . ..

. E08 ......... .... .. .... ......... ..... ..... 5 17A 13 ...... .s.P..L.aY ...................................... .....1.1^...... .............. . ............. I............................. none. ..................................

................................ .......... E085 18D 9 ... . ".X.a.Y............................................ 1.1.2................................................................

I................ .

none.....................

......................... E08 5 19A 2.................SRLAY .112............................. bl erion .......... os..... n ..................

...............................

n.........A one

............................ ........ E08... 6 12C 12 sP,L.aY ...................................... . .....1.1.2 ...... ..........................................................

....................................................

.n,one.......................... :.

..................... E086 6 D 2..... ............... ..sP..r.a.Y ...........................................1..1....2. ................................. .......

I ........................

none..................................................... E08 4 15A 8,,,

..................................... ....... ,..... . sP, ra,Y..................................... ...... 10 below

erosi........................

............................................................................. on no.ne

.............................................. E08 3 2C 11 s.P...a.Y........................................7.5 ....................................... ...............................

...............................

none

............................................. E08 13D 15 sP..r.ay .

............................................2...00?................................................................

.............................................. .......

,none............................

............................................. E08 5 16D15 s.P..L.a.Y............................................600+... extensive,

. 9...........................

...............................

.................................................................. none

. ...................................................................... ............................... ..................

fainter out ..................................... to.................. ..................................................................

.................... .......................................................................... a.P.RCM ...... Hull................... ..................................................................

........................... ..... E08 6 1 .... ... s.P..L.a.Y ........................... ..... 900 ........:..... ...... ... . none..................... 6.

..................... E086 6D 

.................... 7 s. P..L.a.Y............................................840?................................................................

...............................

n,one.....................

...................I.. E08 6 7A......10.....

.......................................

. ....

......

s.P..L.aY............................................168?........

.......................................................

.....................................................................................................................................................................................................................

......... : ..........

hike ....... spraY................... .......

..........................................................

...............................

none....................................................

..................................................................

...............................
7/2/95 4:35 PM 6/23/95.rev 24

crater survey summary as of 4/11/92

wafer mag area scanned # of craters density sigma X41

E08-3-15H 300 1 cW2 55 55 13.48

E08-3-2B 300 1 cm^2 66 66 12.31

E08-3-9C 300 1 cm^2 53 53 13.74

E08-4-1 1 D 300 1 cW2 41 41 15.62

E08-4-14C 300 1 cW2 61 61 12.8

E08-4-4D 300 1 cm"2 85 85 10.85

E08-4-4D1000.2 1000 1 cW2 211 211 6.88

E08-4-4D2 300 1 cW2 67 67 12.22

E08-4-8B 300 1 cW2 73 73 11.7

E08-6-3H 300 1 cW2 66 66 12.31

E08-6-3fl1000 1000 0.7272cW2 49 67.4 14.29

E08-6-3000f 300 2.1 cm", 2 40 19 15.81
SIMS CHEMICAL ANALYSIS OF EXTENDED IMPACT FEATURES FROM THE

TRAILING EDGE PORTION OF EXPERIMENT AO187-2

Sachiko Amari, John Foote, Charles Simon,

Pat Swan, Robert M. Walker, Ernst Zinner

McDonnell Center for the Space Sciences

Washington University

One Brookings Drive

Saint Louis MO 63130-4899 USA

Phone: 314-889-6257, Fax: 314-889-6219

Elmar K. Jessberger, Gundolf Lange, Frank Stadermann

Max-Planck-Institut fur Kernphysik

Postfach 103980

6900 Heidelberg, Germany

SUMMARY

One hundred capture cells from the trailing edge, which had lost their cover foils during flight, were

optically scanned for extended impact features caused by high -velocity projectiles impinging on the cells

while the foils were still intact. Of 53 candidates, 24 impacts were analyzed by secondary ion mass

spectrometry for the chemical composition of deposits. Projectile material was found in all impacts, and at

least 75% of them appear to be caused by interplanetary dust particles. Elemental ratios are fractionated,

with refractory elements enriched in the impacts relative to interplanetary dust particles collected in the

stratosphere. Although this could be due to systematic differences in the compositions, a more likely

explanation is volatility fractionation during the impact process.

INTRODUCTION

The main scientific objective of LDEF experiment AO187-2 was the collection of interplanetary dust

material in space and its elemental and isotopic analysis in the laboratory. Although interplanetary dust

collected in the upper atmosphere has been available for analysis in terrestrial laboratories for more than a

decade (e.g., refs. 1, 2), the stratospheric collection undoubtedly is biased since not all extraterrestrial dust

particles entering the Earth's atmosphere are collected. For example, cometary dust particles have, on

average, a higher velocity and are therefore expected to have a much smaller survival probability of

atmospheric entry than dust grains originating from asteroids (refs. 3, 4). In order to obtain an unbiased

sample of interplanetary dust it is necessary to collect this material in space. LDEF provided an

unprecedented opportunity for this purpose, combining large collecting areas with long exposure times.

A fundamental problem for the collection of interplanetary dust material is the high relative velocity

of dust grains (10-15 km/sec). At these high velocities a major fraction of projectile material is lost upon

impact with most collection surfaces. A viable compromise is to forgo the collection of solid dust grains

503

PRECEDING A E Pj ^--
Pd coat 000 A°)

stic roil (2.5 μm)

:oat (1000 A*)

target

0.2

or fragments thereof and to concentrate on the collection of their atoms in capture cells. LDEF carried

several capture cell experiments (AO023, A0138-2); the principle of A0187-2 is shown in Figure 1. A

target plate is covered by a thin foil separated by a small distance. A high velocity dust grain of sufficient

size penetrates the foil and normally is disrupted in the process, spreading out into a shower of debris.

This shower impacts the target plate, being further disrupted, melted and vaporized. ' The projectile

material ejected from the impact zone is collected on the backside of the foil and then analyzed.

Micrometeorold

Figure 1. Principle of capture cell of experiment AO 187-2.

A series of simulation experiments on laboratory dust accelerators proved this concept to be viable

(refs. 5-7): projectile material could indeed be collected on the surface of the target plate and the backside

of the foil and its elemental and isotopic composition measured. Since the collected material exists as a

thin surface deposit, secondary ion mass spectrometry (SIMS) with its extremely high surface sensitivity

proved to be the best-suited analysis technique. In fact, since one of the main objectives of the experiment

was the isotopic measurement of dust material, A0187-2 was originally conceived and optimized for

SIMS analysis. The choice of materials was largely determined by the requirements for extreme purity and

high ion yields for SIMS analysis.

EXPERIMENT DESCRIPTION AND PRELIMINARY ASSESSMENT

LDEF experiment A0187-2 consisted of 237 capture cells, each 8.6 x 9.4 cm in size. A capture cell

in turn consisted of four polished high purity germanium plates, 42 x 39 x 0.5 mm, covered with a plastic

foil separated from the Ge plate by 200gm. The Ge plates were glued to an Al base plate, the 2.5 gm thick

mylar cover foil was coated with 1300 A of Ta on the backside and 100 A of Au-Pd on the front side. Ta

was chosen to optimize the SIMS analysis of deposited projectile material; Au-Pd was chosen to protect

the foil from erosion by atomic oxygen in the residual atmosphere impinging on the leading edge of LDEF

(refs. 8, 9).

The capture cells occupied locations on three different trays. A full tray, E8, on the leading edge

contained 120 cells, 77 cells were mounted on tray E3 and 40 took up a third of tray C2, both on the

trailing edge. By having capture cells on both the leading and. the trailing edge, the experiment was

expected to obtain information on both interplanetary dust and man-made space debris in low Earth orbit.

After the return of LDEF it was found that all capture cells on the leading edge tray E8 had lost their

plastic-metal foils and only 12 cells on the trailing edge had retained them, 11 on tray E3 and one on tray

C2. Four capture cells from tray E8 and 5 cells without foil from tray E3 were shipped to MesserschmittBolkow-Blohm in Germany, the rest of the cells went to Washington University. At present we do not

know why the foils failed or when this happened. The fact that 12 intact cells were found on the trailing

504
edge indicates that the failure mechanism

probably was not the same for the two

10 7 locations. Atomic oxygen erosion starting

from impact holes or spots with damages in

the protective metal coating is a likely cause

for the complete failure of the cells *on the 10 

6

leading edge of tray E8. The capture cells on

the trailing edge, however, never were r

5

exposed to an atomic oxygen flux. A

U 10 combination of embrittlement by solar UV

and stress failure under thermal cycling is a

possible cause but this hypothesis has to be 104

substantiated by future tests. If we assume

that the failure of foils on the trailing edge is

an exponential function of time, 67% of the 103

cells would have been still intact after one

year, the nominal deployment duration for 107

LDEF.

^—

2A me

27 Ju+

1]/ —^— 40Si+

---a— Ica

0 16

EIZ

—^— 181Ta+

Profile across plastic foil

0 100 200 300 400 500 600 700 800 900

Profile across Ge

wafer

Preliminary optical microscope 106

examination of cells from the trailing edge

that had lost their cover foils (bare cells)

-

showed numerous "extended impact features" 0 105

as well as typical hypervelocity impact craters U

produced by direct hits. The extended impact

features resembled laboratory simulation 104

impacts produced by projectile material that

had penetrated plastic foils and had suffered

disruption. Apparently the extended impact 103

features found on the bare LDEF cells were 0 100 200 300 400 500 600 700 800 900

produced by high velocity impacts onto the

cells while the foils were still intact. Since Distance (μm)

prior simulation studies (ref. 7) had shown Figure 2. Lateral elemental profiles across plastic

that extended impacts on the Ge plates foil and Ge wafer of the same simulation impact.

contained sufficient projectile material for

chemical and isotopic analysis by SIMS

(Fig. 2), we first concentrated our analysis effort on the extended impacts. found in the bare LDEF capture

cells from the trailing edge (trays E3 and C2). These were the best candidates to contain impacts of

interplanetary dust particles with a minimum contribution from orbital debris. Furthermore, foil survival

on 10% of trailing edge cells compared to none on the leading edge indicated that even foils that failed

lasted, on average, longer on the trailing than the leading edge.

All 100 bare capture cells from E3 and C2 in our possession were optically scanned for impact

features. During the scanning we developed criteria for the classification of these impacts and for the

selection of candidates for SIMS analysis. All selected candidates were further documented in a scanning

electron microscope (SEM). To date, a subset of these candidates has been analyzed by SIMS for the

chemical composition of deposited material.

505
Figure 3. Crater produced by hypervelocity

impact onto Ge wafer without cover foil.

OPTICAL, AND SEM CHARACTERIZATION

All bare cells in our possession from the trailing edge, 61 from tray E3 and 39 from tray C2, were

scanned under oblique illumination in an optical stereo microscope with a 12x objective and 20x eyepiece.

The Al plates with the Ge wafers were mounted on a scanning stage whose position could be read with an

accuracy of 50 μm. The wafers were scanned a row (of 6.0 mm width) at a time. Recorded were the

locations of impact features and their sizes and other interesting properties. Among the impacts we

distinguished between "craters" and "extended impacts." Since Ge is very brittle, craters produced by

direct hits (i.e. without penetration of a foil) are not likely to contain much residual material from the

projectile and this expectation was confirmed by subsequent analysis. Figure 3 shows a SEM image of a

crater.

The extended impacts are the most

interesting since they are expected to

contain projectile material. They range

from 200 μm to 4000 μm in diameter and

were divided into two categories, A and B.

Category A comprises larger impacts that

are expected to contain deposits and are

high priority candidates for SIMS analysis.

Category B impacts are smaller and will be

studied last. Features that could not be

recognized with certainty as extended

impacts in the optical microscope were

classified as "possible extended impacts

(Category A or B)," and were examined in

more detail in the SEM.

Extended impacts of category A and B

were further classified into four subcategories according to their morphology.

1) Craters surrounded by deposits (CD).

2) Ring-shaped features (RI).

3) Sprays (SP).

4) Spider webs (SW).

Figure 4 shows SEM micrographs of one of each morphology. The more detailed SEM images revealed

that in many cases an extended impact showed features of different categories (e.g. a crater surrounded by

deposits also had spider web features).

Scanning in the SEM was performed with a twofold purpose:

a) To check all features that had been classified as "possible extended impacts" during the initial

optical scanning to determine which of them are true "extended impacts."

b) To document in detail all extended impacts to be selected for SIMS analysis.

Table 1 gives a summary of the results of the optical scanning. So far, 98 of 157 possible extended

impacts have been examined in the SEM and five of them have been reclassified as extended impacts (2

CD, 3 RI).

506
Figure 4. Morphologies of extended impacts: Craters surrounded by

deposits (upper left), ring (upper right), spray (lower left), and

spider web (lower right).

Table 1. Classification of impacts on bare

capture cells from the trailin g edge

Extended Impacts CD RI SP SW Total

A 14 8 S 23 53

B 5 42 94 14 155

Possible Extended

Impacts A 157

B 177

Craters 203

During the SEM documentation of extended

impacts energy dispersive x-ray (EDX) spectra

were obtained in most cases, especially if

fragments were observed in the area of the

impact. however, fragments usually turned out

to be pieces of the Ta coating of the mylar foil or

other apparent contaminants. Generally it was

not possible to detect any elements besides Ge.

An exception was Si which is present in

quantities detectable by EDX on all Ge wafers

507
from the leading and trailing edge. The Si concentrations on the wafers are non-uniform, being highest on

the edges and lowest in the middle of the Ge plates. The most likely cause for this ubiquitous Si

background is outgassing or migration of the RTV used to bond the Ge onto the Al substrate (in spite of

the space rating of this material). This unfortunate circumstance deprived us (with a few exceptions) of the

opportunity to measure one of the most important cosmochemical elements in the projectile deposits.

A comparison of the extended impact features on Ge from the trailing edge and simulation impacts

produced on the same foil-target assembly in the Munich plasma dust accelerator (refs. 10, 11) at velocities

between 3 and 8 km/sec shows significant differences. The LDEF impacts are, on average, larger and

much more irregular. The simulation impacts usually are spider webs with a high degree of rotational

symmetry or ring-shaped features with typical diameters of 100-200μm. There are two possible

explanations for the large irregular impact features found on the Ge plates from the trailing edge. One is

that many impacts were produced by projectiles that hit the capture cells at oblique angles. The second is

that the foil had already been damaged and some of it had curled up when the impact occurred, leading to a

much more complex foil-target geometry than for the simulation impacts, which were produced at normal

incidence.

SIMS ANALYSIS OF EXTENDED IMPACTS

For SIMS analysis the Ge wafers were cut into smaller pieces containing extended impacts of

interest. This was done by a newly developed laser cutting technique, which avoids any of the

contamination incurred by sawing. A CW YAG laser beam of 1.06 gm wavelength was focussed onto the

rough backside of the Ge wafer (this side has a higher absorption at this wavelength than the polished

front side). At a power of 50 W a short scan across the wafer at a speed of 5 cm/sec was sufficient to

cause a break along the scanned line most of the time. Sometimes the wafers broke along other defects or

along crystal boundaries; however, in all such cases intact pieces of appropriate size could be obtained for

ion probe analysis.

To date 24 of a total 53 extended impacts of category A have been analyzed by SIMS for the

chemical composition of projectile deposits. All measurements were made on the Washington University

ion microprobe, a modified CAMECA IMS 3f instrument. For chemical analysis we obtained lateral

scanning profiles across the impact features. For this purpose at each analysis point an O- primary ion

beam of 1-2 nA current was rastered over an area of 40gmx40μtm. As the primary . ion beam sputtered

away the surface of the analyzed sample layer by layer, positive secondary ions selected from the central

portion of the rastered area by a beam aperture were mass analyzed in a double focussing magnetic mass

spectrometer and counted by an electron multiplier detection system.

Multi-element depth profiles are obtained by cycling the mass spectrometer through a set of isotopic

masses of the selected elements. After analysis of a given area consisting of 40 cycles the sample is

stepped (by 40 or 50 gm) to the next area. Fig. 5a shows a SEM micrograph of an extended impact after

two step-scanning analyses were made on this sample. The individual depth profiles were integrated over

cycles 4 to 40 to obtain lateral profiles in the form of the integrated secondary ion intensity as a function of

lateral distance. The first three cycles were not included in order to reduce the effect of surface

contamination and because a variety of artifacts are encountered during sputtering of the very surface.

508
0'

o6.

__O_ 24Mg+

5 ^% G^ — 0 27 A1+ 0 /® e—®—®_o _O— 2sSi+

40 ca^

04

f^

48Ti+

/ —^— 56Fe+

6o

o3 

—,8r— Ni + —^— 72Ge

OZ

01

^ 1 0

U

Ion signals associated with material

from the impacts could be detected in all 24

analyzed impact areas but large variations

were observed between individual impacts.

For example, the ratio of the maximum

24Mg + signal to the 72Ge + signal for an

individual lateral intensity profile varies over

almost 5 orders of magnitude.

The ideal case is shown by the profile

of Fig. 5b, which corresponds to the top scan

in Fig. 5a. This scan has well defined

maxima for all the isotopic masses measured

except for 72Ge+. It is one of the few cases

where the 28S i + also displays a clear

maximum above background; the latter,

however, is much higher for this element

than for all the others (since the yield of

positive secondary ions is less for Si than for

Mg, Al, Ca and Fe; this discrepancy in the

background is actually much larger than is

indicated by the plot of Fig. 5b). The profile

across impact E03-2-19C-1 is also one of the

few which gives a clear signal for Ni + at

mass 60. The reason is that the signals

associated with impact deposits are relatively

high compared to the Si background. In

most other cases, these signals are much

lower so that the molecular interference from

28SiO2+

 dominates at mass 60.

In order to obtain elemental

abundances, the ion yields of different

elements as well as the isotopic abundances 0

have to be taken into account. Table 2 gives M

sensitivity factors S relative to Si so that

a^

CE — Ei I

/S EI/Si

Csi ISi

where C are the atomic concentrations and I

are the secondary ion signals (corrected for

isotopic abundances) for the element of

interest and the standard element Si. The

sensitivity factors were determined from

measurements on four different glasses

(Lunar Analog Glass, Solar Glass NTR-1,

Window Glass and Dunite Glass).

0 100 200 300 400 500 600 700

0 100 200 300 400 500 600 700

Distance (μm)

Figure 5. Ion microprobe elemental scans across

impact E03-2-19C-1. Profiles in b and c correspond to the upper scan in the SEM micrograph.

509
Table 2. Secondary ion

sensitivity factors

relative to Mg.

Element S

Na 3.28 ± .15

Al 0.77 ± .09

Si 0.13 ± .01

Ca 1.47 ± .24

Ti 0.50±.04

Cr 0.38 ± .15

Mn 0.51 ± .09

Fe 0.47 ± .07

0 500 1000 1500 2000

Because of the problems with Si contamination of the Ge

wafers we normalized the lateral intensity profiles to Mg by applying

the relative sensitivity factors of Table 2. The resulting profiles of

atomic elemental ratios are shown in Fig. 5c. One feature typical for

almost all impacts is apparent from this figure: elemental ratios

change across a lateral profile or, in other words, the deposits from

the impact have different spatial distributions for different elements.

For example, the Fe/Mg ratio has a minimum at lateral position 200

μm, where all the elements show a maximum, and changes by more

than a factor of two 80-100 μm to the left and right of the maximum

position. This can also be seen directly in Fig. 5b where the 56Fe+

profile is slightly wider between positions 100 μm and 300 μm than

the 24Mg+ profile. This means that Fe apparently is distributed over

a wider area than Mg.

Most impacts show even more complex

distributions of the deposited elements. An

example is impact CO2-1-20D-2 whose SEM

micrograph after SIMS analysis is shown in

Fig. 6a. The corresponding lateral intensity

profile is displayed in Fig. 6b. There are

several interesting observations to be made

on this impact, which was classified as CD

(crater with deposits). The first is that the ion

signals of elements apparently deposited from

the projectile (Mg, Ca, Fe) are much lower in

the crater itself (dip in the middle of the

profile) than in surrounding areas. Secondly,

the concentrations of Mg and Fe are much

higher to the left of the crater than to the

right, although on the SEM micrograph the

area to the right shows much more

it in the impact. The reason for this

apparent paradox is that what is "seen" in the

SEM is mostly damage to the Ge surface by

high-velocity debris from the impact, which,

however, contains only little deposited

material, while the deposits themselves are

not seen in the SEM. Finally, in this impact

different elements have very different spatial

distributions: the 56Fe+ signal is higher than

the 40Ca+ signal to the left of the crater, but

lower to the right. It is likely that such

changing elemental ratios reflect

heterogeneities in the chemical composition

of the original projectile.

101

10'

10`

0

U 10

10`

10:

Distance (μm)

Figure 6. Ion probe scan across impact

CO2-1-20D-2, a crater with associated deposits.

510
Scan 1

Scan 2

a

1

O

U 1

1 07

_El— 24M g+

 1 0— 27AI+

4 

101-

,^ --0-- 40Ca+

—!— 48Ti+

U —^ 72Fe+ 104

—^-- Ge

103

CO2-1-14C-2 Scan 1 b

102,1

0' 100 200 300 400 500 600 700 800 900

101 I..............................................

07

ob

_q_ 24M8+

q/ _ 0 — 27 Al'

O S p -

q

ep —p— 40 CaC+

--l-- 48Ti+

56F,+

4 —^ 72+

0 qP—q

--^ Ge

03

CO2-1-14C-2 Scan 2 d

02

0 100 200 300 400 500 600 700 800 900 1000

101

CO2-1-14C-2 Scan 2

100

„q -q—d

—0 AI/Mg

03 Ca/Mg—O—

04 1

/ r` —f— Ti/Mg

10 \\Y// _O— Fe/Mg

N

W

--6 AVMg

—O— CafMg

pp ,^ p q

^

--f— Ti/Mg

100

O

10.1

41

W

10.2

3 I CO2-1-14C-2 Scan 1 C I 3

10' ,- lo'

e

0 100 200 300 400 500 600 700 800 900 0 100 200 300 400 500 600 700 800 900 1000

Distance (μm) Distance (μm)

Figure 7. Two ion microprobe elemental scans across the same extended impact.

511
An even more extreme example of elemental heterogeneity is shown in Fig. 7, depicting a large

extended impact (CO2-1-14C-2) classified as SW (spider web) together with the results of two lateral

scans (the short scans in the SEM micrograph). Not only do the absolute concentrations differ between

the two scans (Fig. 7b,d) but there are also large differences in the elemental ratios (Fig.7c,e).

The non-uniform distribution of different elements in the deposition area of a given extended impact

makes it difficult to obtain average elemental ratios. As a compromise we have taken elemental ratios

determined at the maximum of the 24Mg+ signal for a given scan. Histograms of these elemental ratios are

plotted in Fig. 8 together with histograms of the same ratios measured by SIMS on individual stratospheric

dust particles of probable extraterrestrial origin (ref. 12). Chondritic compositions are indicated for

reference. The ratios measured in projectile deposits on the LDEF Ge wafers not only show much wider

AI/Mg Chond. LDEF

f

1 1 111 1 iii sil l . 11

IDP

Y,

a

301 .01 0.1 1.0 10

Ti/Mg LDEF

Chond.

tar..

IDP

Ca/Mg LDEF

Chond.

M.

MINER' r MR,

IDP

fr:;

)01 .01 0.1 1.0 10

Fe/Mg LDEF

Chond.

IDP

a

MM

MO L:1121§ ME

)001 .001 .01 0.1 1.0 .01 0.1 1.0 10 100

Figure 8. Histograms of elemental ratios in LDEF deposits

and interplanetary dust particles.

512
1

°

0

-1.^^

2

-3

a

°

-4

10'4 10-, 10-` 10"

Ti/Mg

10

10

10

bao

10

10

10

10

10°

102

101

100

t^.A 10.1

10.2

103

10.4

10,`

°

°

°

°

^_ •

°

°

Q

°

C

10-1

10 ° 101 10 2

Fe/Mg

distributions than those of IDPs but the mean of

the distributions are systematically shifted relative

to one another. This shift is toward lower values

for Fe/Mg but toward higher values for the other

three ratios, A1/Mg, Ca/Mg, and Ti/Mg.

There are at least two explanations for these

differences. The first is simply that the particles

whose material was collected on the Ge wafers

on LDEF have chemical compositions that differ

significantly from those of IDPs collected in the

stratosphere. The second is that the impact

process caused strong fractionation between the

elements so that the compositions of the deposits

do not accurately reflect those of the projectiles.

One reason the particles that impacted LDEF have

compositions different from IDPs could be that a

major portion of them are not interplanetary dust

but man-made debris. This, however, is unlikely

in our case. First, collection on the trailing edge

discriminates to a large extent against orbital

debris. Furthermore, Mg is the dominant

element in most impacts compared to Fe, Al, Ca

and Ti. This is not expected for most man-made

debris in orbit, which in this size range is

presumably dominated by Al-oxide particles

from the exhaust of solid fuel rockets.

Moreover, we did not detect any impacts that

contain primarily Al (Fig. 9).

Before we consider the possibility of

differences in the chemical composition of

interplanetary dust particles collected on LDEF

and in the stratosphere, we have to discuss

elemental fractionation during the impact process.

There is evidence for such fractionation from

simulation impacts onto the same foil/Ge wafer

targets as flown on LDEF. The analysis of 12

extended impacts on the Ge produced by Lunar

Analog Glass and Solar Glass showed

fractionation between Mg and the other elements

in the deposits with average fractionation factors

relative to Mg of 0.28 for Fe, 0.58 for Si, 1.60

for Al, 1.95 for Ti and 2.41 for Ca. A

fractionation factor smaller than one means that,

compared to the projectile, less of the element is

found in the deposition area than Mg and the

° LDEF

® IDP

o Chon.

°

°

® - °%

°

°

°

a

10 .3

10.210.1100

101102

Ca/Mg

Figure 9. Scatter plots of elemental ratios in

LDEF impact deposits and in interplanetary

particles. Also shown are chondritic ratios, the

elemental fractionations determined from simulation impacts (solid arrows) and the extension

of these fractionations (light arrows).

102

101

100

bA 

10.1

d 10-2

10-3

10-4

513
opposite is the case for fractionation factors greater than one. We note that elemental fractionations are

related to the relative volatilities of the elements during high temperature evaporation and condensation: the

elements Fe and Si are more volatile than Mg and are depleted in the deposits relative to Mg while Al, Ca

and Ti are more refractory and are enhanced relative to Mg.

During the impact apparently a large part of the projectile either melts or evaporates. Elements with

different volatilities behave differently during this process. More volatile elements such as Fe are almost

completely vaporized and expand into a larger volume before they condense onto the Ge and foil surfaces.

More refractory elements, on the other hand, either remain in the melt or, if they evaporate, condense

sooner and therefore onto a more limited area. Except for the (small) fraction that escapes through the

penetration hole, all of the projectile material is retained inside the capture cell but some (preferentially the

more volatile elements) is distributed over such a large area that it is lost in the background. For example,

if the material of a 10μm projectile is spread out over an area of 1 mm diameter, its thickness is only 2.5

atomic monolayers, only 1/6 of a monolayer for the 4 mm largest observed extended impact.

Figure 9 shows scatterplots of pairs of elemental ratios for the LDEF deposits and individual IDPs.

Also shown are the chondritic compositions and the shifts in these compositions if this material

experienced the same elemental fractionations as those determined in the impact simulation experiments.

The differences between most LDEF deposit compositions and the IDP compositions qualitatively agree

with the shifts expected from fractionation during impacts, except that the differences are much larger than

the shifts predicted from fractionation. However, we cannot exclude the possibility that elemental

fractionations are actually much higher during impacts on LDEF than during simulation impacts. We have

already pointed out that the LDEF extended impacts on the Ge are generally much larger than the

simulation impacts from which the above fractionation factors were derived. It is reasonable to expect that

elemental fractionation factors increase with the size of the extended impact feature. However, the

uncertainty in this extension, the extremely irregular structure of most impact features and the fact that the

fractionation factors undoubtedly depend on the composition of the projectile itself set a fundamental limit

to the extent to which the projectile composition can be derived from the measured composition of the

deposits.

Tentatively we can identify most of the LDEF impacts as being caused by cosmic dust particles. Six

data points in Fig. 9 fall completely outside of the predicted trend due to elemental fractionation (they are

enclosed in ellipses in the Figures). Four of them have extremely high Al/Mg, Ti/Mg and Ca/Mg but also

very high Fe/Mg and are likely to be contaminants. The other two have low Al/Mg ratios. This leaves us

with 18 (75%) impacts of likely interplanetary origin. While some of them have only little deposited

material, some have plenty of it (see, e.g., Figs. 5, 6 and 7) and are candidates for future isotopic

measurements. We also plan additional chemical analyses of elements that can easily be detected as

negative secondary ions such as C, O, and S.

514
CONCLUSIONS

SIMS analyses of 24 extended impact features on Ge surfaces from "bare" trailing edge capture cells

show evidence for projectile material in all of them, but there are large variations in the detected

concentrations.

2. The deposits are very thin and cannot be detected by EDX analysis; SIMS appears to be the only

method to detect them.

3. Elemental concentrations on the Ge do not correlate exactly with impact features seen in the SEM

. images; the latter are dominated by damaged regions which contain little projectile material.

4. There is evidence for large variations of elemental ratios within a given extended impact, indicating a

heterogeneous chemical composition of the projectile.

5. Comparison with simulation impacts indicates that most LDEF impacts analyzed by SIMS were

caused by small (<10μtm) projectiles.

6. At least 75% of the analyzed impacts appear to be from interplanetary dust particles but elemental

ratios scatter much more than those measured in IDPs collected in the stratosphere.

7. Elemental ratios are also shifted compared to IDPs, with refractory elements being relatively

enriched. These shifts are likely to be due to elemental fractionation effects caused by evaporation

during the impact process, but systematic differences between IDPs and LDEF impacts cannot be

ruled out.

FUTURE WORK

Fractionation effects should be much less pronounced in isotopic ratios than in elemental ratios.

Moreover, such effects will not obscure large anomalies of specific isotopes (if present) such as those

found by us in studies of interstellar grains isolated from meteorites (ref. 13). As a consequence, future

work will concentrate on isotopic measurements in those impacts that have been found in our initial survey

to contain sufficient amounts of projectile material.

We have also refrained from studying the 12 intact (precious) capture cells until our handling and

analysis techniques had been perfected on the more abundant, extended impacts found in the bare cells.

The analysis of the intact cells should provide a critical test of the usefulness of our capture cell concept

for future space flight experiments.

Detailed studies of impacts on the cells from the leading edge tray E8 should yield data relevant to

the orbital debris problem. The ratios of extended impacts to single craters in these cells should allow us

to determine when the plastic cover foils failed on the leading. edge capture cells.

This work was supported by NASA Grant NAG-1-1174 and ESTEC AOP/WK/303284.

515
REFERENCES

1. Bradley, J. P.; Sandford, S. A.; and Walker, R. M.: Interplanetary dust particles. In Meteorites and

the Early Solar System, eds. Kerridge, J. F.; and Matthews, M. S.; University of Arizona

Press, 1988; pp. 861-895.

2. Brownlee, D. E.: Cosmic dust: collection and research. Ann. Rev. Earth Planet. Sci., 13, 1985,

pp. 147-173.

3. Flynn, G. J.: Asteroids, Comets and Meteors III, 1989, pp. 59-62.

4. Flynn, G. J.: Survival of large micrometeorites on atmospheric entry: implications for their sources

and the flux of cometary dust. Lunar Planet. Sci. XXII, 1991, pp. 393-394.

5. Zinner, E.; Kuczera, H.; and Pailer, N.: Simulation experiments for the chemical and isotopic

measurements of interplanetary dust on LDEF. Lunar Planet. Sci. XIII, 1982, pp. 891-892.

6. Jessberger, E.; Kuczera, H.; Lange, G.; Sutton, S.; and Zinner, E.: Ion microprobe analyses

of simulated LDEF impact residues. Lunar Planet. Sci. XVI, 1985, pp. 400-401.

7. Lange, G.; Eigner, S.; Igenbergs, E.; Jessberger, E. K.; Kuczera, H.; Maas, D.; Sutton, S.;

Weishaupt, U.; and Zinner, E.: Ion microprobe sensitivities and their application to

multielement analysis of LDEF impact residues. Lunar Planet. Sci. XVII, 1986, pp. 456-457.

8. Fraundorf, P.; Lindstrom, D.; Pailer, N.; Swan, P.; Walker, R.; and Zinner, E.: Rapid erosion of

plastics in near-earth orbit and a means of prevention. Lunar Planet. Sci. XIV, 1983, pp. 205-

206.

9. Fraundorf, P.; Lindstrom, D.; Pailer, N.; Sandford, S.; Swan, P.; Walker, R.; and Zinner, E.:

Erosion of mylar and protection by thin metal films; AIAA Shuttle Environment and

Operations Meeting; 1983; Paper 83-2636, pp. 131-137.

10. Fechtig, H.; Grun, E.; and Kissel, J.: Laboratory simulations. In Cosmic Dust, ed. McDonnell, J.

A. M.; Wiley and Sons, New York, 1978; pp. 607-669.

11. Igenbergs, E.: Ein newer Beschleuniger fur die Simulation von Mikrometeoriten.

Forschungsbericht, 1974, pp. BMFT-FBW 1974-03.

12. Stadermann, F.: Rare earth and trace element abundances in individual IDPs. Lunar Planet. Sci.

XXII, 1991, pp. 1311-1312.

13. Zinner, E.; Tang, M.; and Anders, E.: Interstellar SiC in the Murchison and Murray meteorites: I

sotopic composition of Ne, Xe, Si, C, and N. Geochim. Cosmochim. Acta, 53, 1989, pp.

3273-3290.

516
SIMS CHEMICAL ANALYSIS OF EXTENDED IMPACTS ON THE LEADING

AND TRAILING EDGES OF LDEF EXPERIMENT A0187 -2

S. Amari, J. Foote, P. Swan, R. M. Walker, E. Zinner

McDonnell Center for the Space Sciences and Physics Department

Washington University

One Brookings Drive

St. Louis, MO 63130-4899

Phone: 314/935-6257, Fax: - 314/935-6219

G. Lange

Max-Planck-Institut fur Kernphysik

Postfach 103980

D-6900 Heidelberg, Germany

Phone: 6221 516 247, Fax: 6221 516 540

SUMMARY

Numerous "extended impacts" found in both leading and trailing edge capture cells have been

successfully analyzed for the chemical composition of projectile residues by secondary ion mass

spectrometry (SIMS). Most data have been obtained from the trailing edge cells where 45 of 58 impacts

have been classified as "probably natural" and the remainder as "possibly man-made debris." This is in

striking contrast to leading edge cells where 9 of 11 impacts so far measured are definitely classified as

orbital debris. Although all the leading edge cells had lost their plastic entrance foils during flight, the

rate of foil failure was similar to that of the trailing edge cells, 10% of which were recovered intact.

Ultra-violet embrittlement is suspected as the major cause of failure on both leading and trailing edges.

The major impediment to the accurate determination of projectile chemistry is the fractionation of

volatile and refractory elements in the hypervelocity impact and redeposition processes. This effect had

been noticed in a simulation experiment but is more pronounced in the LDEF capture cells, probably due

to the higher average velocities of the space impacts. Surface contamination of the pure Ge surfaces

with a substance rich in Si but also containing Mg and Al provides an additional problem for the

accurate determination of impactor chemistry. The effect is variable, being much larger on surfaces that

were exposed to space than in those cells that remained intact. Future work will concentrate on the

analyses of more leading edge impacts and the development of new SIMS techniques for the

measurement of elemental abundances in extended impacts.

PRECEDING P 513

fa _"46 . h @s

. r,!
INTRODUCTION

LDEF experiment A0187-2 consisted of 228 Ge-mylar cells for the capture of interplanetary dust

material. The principle of the experiment and a more detailed description of the capture cells is given by

Amari et al. (ref. 1). One full tray of capture cells was exposed on the leading edge and an area

equivalent to a full tray in two locations on the trailing edge.

All cells on the leading edge and 90% of the cells on the trailing edge had lost their plastic covers

(bare cells) during exposure in space. However, Ge plates from both leading and trailing edge bare cells

contain extended impact features that must have been produced by high velocity projectiles while the

mylar foils were still intact. Moreover, these extended impact features contain projectile material that

could be measured by secondary ion mass spectrometry (SIMS), an extremely sensitive surface analysis

technique.

Last year we reported results of the optical scanning of 100 bare cells from the trailing edge as well

as the first results of SIMS analysis of 24 extended impacts on Ge from these cells (ref. 1). In the

present paper we extend the SIMS analysis to 16 additional impacts from bare trailing edge cells and 18

impacts from the 12 trailing edge cells that had retained their plastic covers. We also optically scanned

the Ge plates of 106 capture cells from the leading edge for single craters and extended impacts and

analyzed 11 of the latter by SIMS.

OPTICAL SCANNING FOR SINGLE CRATERS AND EXTENDED IMPACTS

All cells were optically scanned under oblique illumination at a magnification of 240x as

previously described by Amari et al. (ref. 1). The results are given in Table 1. There is a clear

distinction between "extended impact features" and "single craters." The former consist of complex

patterns of debris and ejecta, and must have been produced while the plastic cover foils were in place.

In contrast, "single craters" show no evidence of associated debris deposits and represent direct hits on

the Ge plates after the foils had failed in flight. The distinction between "extended impacts A and B" is

subjective with the former generally being larger than the latter and being visible with the unaided eye.

Although we have chosen to analyze the type A impacts first, we consider it likely that also many of the

type B impacts contain sufficient material for chemical and isotopic analysis.

Table 1. Analysis of Cells on A0187-2

Cells Single Extended Extended Measured

scanned Craters Impacts A Impacts B by SIMS

Ge Foil

Trailing Edge Bare 100 203 53 155 40

Trailing Edge Covered 12 - 20 26 18 5

Leading Edge 106 5121 1

403 1298 1 11

514
Leading Edge

100 200 500 1000 2000 5000

Extended Impact Diameter (μm)

90

80

70

60

50

40

30

20

10

0

18

16

14

12

10

100 200 500 1000 2000 5000

Extended Impact Diameter (μm)

There are several differences between

the impacts on the two sides of the

spacecraft. Figure 1 shows histograms of the

sizes of extended impacts on the leading and

trailing edge cells. As can be seen, the

trailing edge impacts have, on average, much

larger diameters than those on the leading

edge. This is undoubtedly a reflection of the

lower projectile velocities and shallower

impact directions (ref. 2) for the trailing edge

An additional reason could be differences in

the chemical compositions and physical

properties of the projectiles, since a large

fraction of leading edge impacts appear to be

caused by man-made debris (see below),

while those on the trailing edge are

predominately produced by cosmic dust

particles.

Fig. 1. Distribution of the sizes of extended

impacts on Ge plates for both leading and

trailing edge capture cells.

LIFETIMES OF ENTRANCE FOILS - FRONT AND BACK

All of the plastic cover foils on the leading edge failed during flight while — 10% on those of the

trailing edge survived. At first glance it thus appears that there may have been a qualitative difference in

the foil destruction processes between front and back. However, as we will show below, this is a

somewhat misleading impression. While it is true that the foil loss occurred at a higher rate on the

leading edge, foils on this edge lasted for 'long periods of time in space. The difference in foil survival

between front and back is thus more quantitative than qualitative.

Although some corners and edges of many cells contained small pieces of intact or rolled up foil

material, when different foils ruptured they appear to have done so suddenly, exposing a major part of

the area of any given cell to free space. Since direct hits producing single craters are possible only after

the foil has been removed, the density of single craters in a given cell is proportional to the time it was

exposed without a foil provided, of course, that the flux of impacting particles is constant in time.

515
0 20 40 60 80 100 120

20

18

h 16 a

14

U 12

° 10

.a 8

6

z 4

2

0

Consider first the results from the leading

edge cells. Although none of the plastic foils

survived for the entire exposure, it is clear that

many remained in place for a considerable

period of time. In Fig. 2, we show a histogram

of the number of single craters per cell. The

width of the distribution far exceeds that

expected for a single exposure time for all cells

and indicates, in itself, a distribution of survival

times. The locations of individual impacts were

plotted for the two cells with the largest density

of single craters. No clustering was seen,

consistent with the assumption that single craters

represent a random population of impinging

particles.

The maximum number of single craters

per cell is 101. If we assume that the foil on

this cell failed immediately after launch, the

distribution of craters in Fig. 2 would indicate

that more than 50% of the foils survived at least

to the half way mark and that some foils lasted

through almost 90% of the total exposure time

before rupturing.

In contrast to single craters, the density

of extended impacts is a measure of the time

the foils remained in place. However, only a

small fraction of the particles that produce

single craters produce extended impacts that

are visible under the same scanning

conditions. Thus the statistics on extended

impacts are less favorable than those for

single craters. Figure 3 is a scatter diagram

showing the relation between extended

impacts (A plus B) and single craters. This

figure also shows the same data after binning

into groups of 20 single craters and

averaging the number of extended impacts in

each bin. The data show the expected

inverse relationship between number of

extended impacts and number of single

craters (Fig. 3). Furthermore, the best-fit line

through these binned averages intercepts the

abscissa at 111 craters per cell, not very

different from the maximum number of 101

Number of Single Craters per Cell

Fig. 2. Distribution of the number of single craters

per cell for leading edge capture cells. Such craters

are produced only after the entrance foils have

ruptered and their numbers are a measure of the time

different Ge surfaces were exposed to space. The

width of this distribution indicates a considerable

spread in foil lifetimes.

25

U

a^

Q" 20

Cd

a

15

b

-b

10

X

w

o g

z °0 20 40 60 80 100 120

Number of Single Craters per Cell

Fig. 3. Extended impacts and single craters for leading

edge capture cells. The solid squares show averages

for the number of extended impacts versus single crater

counts binned in groups of 20. Since extended impacts

are produced only when the entrance foils are intact

and single impacts only after they have ruptured, there

is an inverse correlation between the two densities.

1 I Leading Edge Cells

i

0 1

i

1

1

1 0

Individual Cells

I I 1 Averages of Bins

o I

P°

I

I

1

° I I I

b° oo b

00 of

0 1 1 °0°

0 90

9 0°1

o 1 0 0 0 o6 O000%

d 0mo6

0

° O I I I

1 0 0 1 1

100

1 I

° 1 0 1 0 I

000 0 ° 0 1 I

1

o ° 0 00 0 1 Q

0 0m o

516
we assumed to be the number of craters on a cell whose foil was removed right after the launch of

LDEF. Thus the two indicators of foil lifetimes yield consistent results and a sizable fraction of the

foils on the leading edge survived a considerable fraction of the total time of LDEF in orbit.

Consider next the data on the trailing edge cells. The 12 cells which remained covered during the

entire period have a total of 46 extended impacts of types A and B for an average of 3.8 impacts/cell.

The bare cells have an average of 2.1 extended impacts/cell, suggesting that the foils lasted, on average,

about half of the total time. This is similar to the result inferred for the leading edge cells from

consideration of the single impact crater data. The first order conclusion is thus that the foil failure rates

are similar for both the leading and trailing edge cells.

While we do not know in detail what caused the foils to fail, certain general aspects of the

problem seem clear. Firstly, since the rates at

which the foils failed were approximately the

same for both the leading and trailing edges, the

same causative factors must be present. Thus

neither atomic oxygen erosion nor enhanced

impact fluxes, which are characteristic of the

front side only, appears to be the principal cause

of failure. However, both effects could have

contributed to an enhanced failure rate of the

leading edge cells.

Some contribution of atomic oxygen

erosion indeed seems likely since we have

evidence that most impacts alone do not destroy

foils. This conclusion is based on the presence

of peculiar elliptical features that accompany

approximately half of the extended impacts on

the leading edge. Fig. 4 shows two such

features that are associated with extended

impacts. The fact that these elliptical features

occur only on the leading edge Ge plates and

only in connection with extended impacts

indicates that they must have been caused by the

interaction of the residual atmosphere, mostly

atomic oxygen, with the penetration hole left by

the high velocity impact. At present we do not

have any detailed understanding of this process.

Foil failure probably results from repeated

stressing of the foils due to cyclical temperature

changes, coupled with degradation of the

mechanical properties of the foils in the space

environment. In spite of the fact that the plastic

was metal-coated, we consider UV

Fig. 4. Elliptical features associated with extended

impacts. These multi-ringed concentric features are

seen in about half of the extended impacts found in

the leading edge cells. Their presence indicates that

the entrance foils did not rupture immediately upon

impact.

517
embrittlement to be a likely source of this degradation.

We plan to continue to address the question of foil lifetimes by determining the density of

small craters (down to <-1 μm diameter) that can be seen by scanning at 1000x in an SEM. A

possible difficulty with this approach, however, is the observation of temporal changes of the flux of

very small particles impinging on the leading edge capture cells (ref. 3).

SIMS CHEMICAL ANALYSIS OF EXTENDED IMPACTS

Background

•

The procedures for the SIMS chemical

analysis of projectile deposits in extended

impacts have been described previously

(ref. 1). To summarize briefly: lateral

multielement profiles across extended impacts

are obtained by integrating secondary ion

intensity depth profiles measured in areas 40

μm apart. From the ion signals we obtain

elemental ratios by applying sensitivity factors

determined from measurements on standards.

Previous measurements have shown that

different elements can be distributed

differently in a given impact, apparently

reflecting compositional heterogeneity of the

projectile. While we plan to use a newly

acquired secondary ion digital imaging system

to determine the spatial distribution of various

elements over the entire impact area, for the

time being we have adopted a compromise —

elemental ratio determinations from lateral

profile data are estimated by taking ion

intensities measured at the maximum of the 24Mg+ signal.

q Trailing edge

® Covered trailing edge

Leading edge q q

CAP

q

E3

• q

® q

[^p

moap U IM

s

104 10' 101

10i10° 10`

28Si+/72Ge

10'1

q Trailing edge

® Covered trailing edge

Leading edge

FA qqqa63

m omMup Go

q q®

10°

+ 10.E

10-2

10.3

104

10

+^ 102

\ 103 +

N 10.4

102

During SIMS measurements of

extended impacts on the Ge plates it became

clear that the sensitivity of the analysis

technique is not one of the limiting factors

(interestingly, SEM-EDS studies of the same

impacts gave no signals of projectile

material, even at low voltages). The major

10'5

1074 10' 10-2 101

101

101 102

28Si +/ 72 Ge

Fig. 5. Surface contamination on Ge target plates in

regions well removed from impact debris.

518
E08-2-7B-5

10

10

10

10

10

10

c

0

10

0 200 400 600 800 1000 1200 1400

U

Distance (μm)

Fig. 6. Signature of an orbital debris impact found in a

leading edge cell. The ion microprobe scan across impact

E08-2-7B-5 shows Al as the only element that is present

at enhanced levels.

-limitation on the SIMS data is rather the high level of contamination encountered on the surface of

the Ge plates. While contamination with Si is worst, high background levels are found also for other

elements. Fig. 5 shows ion signals measured outside of the impact areas normalized to the 72Ge+

signal. Background levels of Mg and Al are correlated with those of Si. The plots furthermore

clearly show that the contamination levels are related to the exposure of the cells during flight: on

average, the backgrounds are lowest on the plates from capture cells that retained their plastic foils

and highest on the plates exposed on the leading edge. While we originally thought that outgassing

of the RTV that was used to bond the Ge

plates to the Al substrate was the main

contamination. The fact that the leading

edge plates have the highest background

levels may be an important clue

suggesting, for example, that redeposition

of atomic oxygen induced erosion

products may be significant.

Analysis of Impacts on the Leading Edge

To date we have performed SIMS

analyses on 11 extended impacts from the

leading edge. In 8 of these impacts

enhancements were seen only for Al.

Fig. 6 shows one of the impacts and the

corresponding lateral ion intensity

profiles. One additional impact showed

enhancements mostly in Ti with minor

Al. Its SEM micrograph and lateral ion

intensity profiles are presented in Fig. 7.

The remaining two impacts have hardly

any elemental enhancements that can be

attributed to projectile material in the

region that exhibits damage features in

the SEM. It has already been mentioned

that the leading edge Ge plates suffer

from extremely high levels of

contamination (Fig. 5), and this may be

the reason that no projectile material

above background could be detected in

these two impacts.

source for the Si contamination, the fact that other elements correlate with the Si demonstrates that

there must be other sources of

519
E08-2-17A-3

_ 24 \4g+

13ROOFMCGRO

"DBQ^ ^ 2?A]+

_o— 28 s;+

bM7 _^- 40Ca+

^O no^M _a 48Ti+

.-- 56

 Fe+

7

2 

Ge+

y^ 181Ta+

O

U 1

The extended impacts from the

leading edge capture cells thus differ

significantly from those from the trailing

edge capture cells in the chemical

composition of their deposits. No impacts

with only Al or Ti deposits such as those

depicted in Figs. 6 and 7 have been seen on

the trailing edge Ge plates. We can thus,

with reasonable certainty, assign the 9

leading edge impacts that contain only Al or

Ti to man-made debris. The first are most

likely Al-oxide particles produced by solidfuel rocket engines, the latter (mostly Ti)

either is a chip of paint or a fragment of

spacecraft hardware. Although the number

of investigated leadin g edge impacts is still

extremely limited, their chemical analysis

shows that they are dominated by man-made

debris.

Analysis of Impacts on the Trailing

Edge

In the present work, we analyzed

another 16 extended impacts from the

bare trailing edge capture cells

(increasing the total number of impacts

from these cells analyzed by SIMS to 40)

and 18 extended impacts from the 12

trailing edge cells that had retained their

foils. Histograms of computed elemental

ratios for all impacts with clear maxima

of the plotted elements in the lateral

intensity profiles (32 of the bare cell

impacts and 16 of the covered cell

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Distance (μm)

Fig. 7. Another probable orbital debris impact in a

leading edge cell. The ion microprobe traverse across

extended impact E08-2-17A-3 shows enhancements of

both Ti and Al.

impacts) are shown in Fig. 8. They are compared with elemental ratios measured by SIMS in

interplanetary dust particles collected in the stratosphere (ref. 4,5). Chondritic ratios are indicated

for reference.

For the Ca/Mg, Ti/Mg and Fe/Mg ratios there appears to be no systematic difference between the

impacts from the bare and covered capture cells. The Al/Mg ratios, however, are on average smaller in

impacts from the covered cells than in those from the uncovered cells. A possible explanation for this

discrepancy is the higher level of contamination on the exposed Ge plates (Fig. 5).

520
AI/Mg Chond.

E2 Covered Cells

EM Bare Cells

LDEF I

t

Ca/Mg Chond. LDEF

IDP IDP I

001 .01 0.1 1.0 10 001 .01 0.1 1.0 10

Ti/Mg LDEF

Chond.

IDP

Offl .

I

.may

i

Fe/Mg Chond. LDEF

IDP

.0001 .001 .01 0.1 1.0 .01 0.1 1.0 10 100

Fig. 8. Histograms of elemental ratios measured in LDEF extended impacts

compared to previous measurements of a set of interplanetary dust particles (IDPs)

collected in the stratosphere. Average chondritic values are indicated by the arrows.

The systematic shift of the elemental ratios measured for extended impact residues compared to

11DPs and chondritic ratios has previously been noted and discussed by us (ref. 1). We pointed out that

laboratory simulation experiments indicated that projectile residue material on the Ge plates is

521
5.0 A,

q Ge Target E-^ U

n Mylar Foil

L. q

0 2.0

W ....

c

1.0 ^

cis

C

.° 0.5

c.^

e^

s.

w

0.2

1500 2000 2500

Melting Temperature of Oxide (° Q

Fig. 9. Element fractionation trends measured in laboratory

impact experiments. The data are from the thesis of G.

Lange Heidleberg, 1986 and were obtained with the W.U.

ion microprobe. The ordinate shows measurements of the

relative abundance of different elements in the impact

debris compared to the abundance of those same elements

in the glass projectiles used in the impact experiments. The

abscissa orders the elements by a volatility index.

fractionated in its elemental composition relative to the original projectile with refractory elements being

enhanced in the deposits relative to less refractory elements (ref. 6). These simulation experiments on

foil/Ge cells identical to those flown on LDEF also showed that the elemental fractionations are larger

for material on the Ge plates than for

material deposited on the backside of the

entrance foil (Fig. 9).

The impacts in the covered trailing

edge cell provided us with the

opportunity to test this elemental

fractionation effect for projectiles

captured on LDEF. So far we have

attempted the analysis of foil deposits

from 5 impacts in the covered cells.

Unfortunately, the SIMS measurements

of the foils are very difficult, mostly due

to extreme embrittlement of the samples

and their failure to stay stretched and

smooth when mounted for ion probe

analysis. We obtained a good SIMS

analysis on only one foil deposit of the

five tried. Data for this impact are

discussed next.

The extended impact on Ge and

the backside of the foil featuring the

penetration hole and signs of secondary

ejecta are shown in Fig. 10 together with

lateral profiles across the Ge impact and

the deposits on the foil. The elemental

ratios obtained from these profiles are

plotted in Fig. 11 and compared to the

fractionation of a projectile of chondritic composition expected from laboratory experiments. As

expected, the material from impact E03-2-11A-3 deposited on the Ge plate is more fractionated than

the material found on the backside of the mylar foil. The relative fractionation for the LDEF impact

is larger than the average obtained from the simulation experiments. This is probably a reflection of

a difference in the impact velocities but could also reflect differences in chemical composition and

physical properties (density, shape) of the projectile.

Although additional measurements on foil deposits are needed, the presence of elemental

fractionations between Ge and foil deposits in one LDEF impact makes it likely that the dominant cause

for the large differences between elemental ratios measured in extended impacts from the trailing edge

and those measured in IDPs is elemental fractionation during the high velocity impact process.

Intrinsic, large differences in chemical compositions between these two populations is less likely,

although still possible.

522
10 

0 104

U

103

—S— 24 MR+

—6 27A1+

—43— 2ISi+

—0 40 Ca+

—f— 48Ti+

56 Fe+

72 Ge

1Nl. +I 

1

E03-2-11 A-3 Ge

107

105,

E03-2-11A-3 Foil

)7^ .mss l,l

—a— 24MR+

) 6. ,A1*8 6_ 27 A1+

N

—.a— 28Si+

5 6 ._0._ 40 Ca+

o.o-c

r;---0— 56FC+

)4 72 GR_ —^— 181.la+

)3

10 F ^ 1

0 200 400 600 800 1000 1200

Distance (μm)

0 200 400 600 800 1000 1200

Distance (μm)

Fig. 10. Ion microprobe profiles on both the Ge target plate and the underside of the entrance foil for

impact E03-2-11A-3. Most of the capture cells lost their entrance foils during flight and those that

survived are extremely brittle and difficult to mount. The data shown are for the only cell for which

it has been proven possible to study impacts in the way that we had originally intended. As expected

from simulation experiments the projectile signals are much higher for the debris on the foil than for

the debris on the Ge target plate.

The presence of elemental fractionations in the impact deposits is the single largest impediment to

accurate determination of projectile chemistry. In principle, all of the projectile material, except the

small fraction that escapes back through the impact hole in the entrance foil, is deposited in the capture

cell, i.e. in our design either on the Ge plate or the backside of the foil. However, more volatile elements

are apparently deposited over a wider area of the Ge plate and foil and, when the surface concentration

becomes too low, can no longer be detected. It is therefore important to measure the surface deposits

over as wide an area as possible. Measuring the radial dependence of the abundances of different

elements may allow the development of normalization procedures that could correct for fractionation

523
10 

bA 10 

z

<^ 10-1

10''

q E03-2-11A-3 Ge

♦ E03-2-11A-3 Foil

® Chondrite

41r13

101

bJJ 10 0

10

cat] 

10'

q E03-2-11A-3 Ge

♦ E03-2-11A-3 Foil

® Chondrite

° s b

2

10-210-1 100 101 10

-2

101 100 101

Ca/Mg Fe/Mg

Fig. 11. Fractionation trends from the data on the intact cell shown in Fig. 10. The arrows indicate the

fractionation trends previously obtained from laboratory simulation experiments of the type shown in

Fig. 9. As expected from the prior work, the projectile material on the Ge plate is fractionated relative

to that on the foil.

effects. In future space experiments, it would be desirable to have partitioned capture cells which would

limit the area on which material from a given impact was deposited. It is not obvious, however, how to

construct such a device while keeping all surfaces accessible to SIMS analysis.

IDENTIFICATION OF THE ORIGIN OF PROJECTILE MATERIAL

In spite of the problems caused by elemental fractionation the abundance data can be used to

decide which LDEF impacts were caused by micrometeoroids and which ones by man-made debris. The

situation is fairly simple for the extended impacts from the leading edge. Eight of these impacts show

only Al enhancements and one shows Ti with minor Al and all can therefore be attributed to man-made

debris with high confidence. Two impacts do not contain any clear enhancements and are thus

unidentified.

The identification of the origin of trailing edge impacts is more difficult. One of them does not

show any noticeable element enhancements and its origin is unidentified. Two impacts have

enhancements in Fe only without any accompanying enhancements in Cr and Ni. They therefore cannot

be caused by stainless steel debris particles. It is not unlikely that the projectiles are FeS particles.

Such particles have been found in the stratospheric dust collection (ref. 7) and unmelted FeS fragments

have been identified in LDEF craters (ref. 8). Since S is much more sensitive when measured as a

negative secondary ion we do not have any S analysis yet on these two impacts but for the time being

tentatively classify them as being of cosmic origin.

There are another four trailing edge impacts for which Fe is the dominant element (always

discounting Si for which, as already discussed, no reliable measurements are possible because of its

524
!!J

extremely high contamination level). In

one case the Fe is associated with Al,

which makes man-made debris the most

likely source for this particular impact.

Although in the other three impacts Fe is

very high, Mg enhancements are also

clearly present. The Fe/Mg ratios are 24.8,

25.7, and 45.2, respectively. With some

elemental fractionation during impact, the

true Fe/Mg ratios of the projectiles are

probably even higher. Although all three

particles could have consisted mostly of

FeS with some chondritic material

attached, we cannot exclude a debris

origin (Cr is low, however). The same is

true for another two trailing edge impacts

in which Al and Ca are dominated by

contamination on the Ge plate and in

which Fe/Mg is high.

The remaining 49 trailing edge

impacts have their elemental ratios Al/Mg,

Ca/Mg, Ti/Mg and Fe/Mg plotted in Fig.

12. Also plotted are the same ratios for

interplanetary dust particles collected in

the stratosphere and for chondrites. The

arrows indicate the directions of elemental

mass fractionation during hypervelocity

102

101

10°

by

10-1

10 -2

10 -3

10 4

10-3

102

101

10°

b.A

10 -1

r-, 10-2

10 -3

104

10-4

10-2 10 -1

101

101 102

Ca/Mg

10-3 10-2

10-110 101

Ti/Mg

102

101

10°

bA

10-1

10-2

10 -3

104

Fig. 12. Elemental ratios measured in the

ion microprobe for trailing edge extended

impacts. The arrows indicate elemental

fractionation trends determined from

laboratory simulation experiments. As

discussed in the text, impacts whose

compositions lie in the shaded regions are

classified as "probably natural" and those

outside as "possibly orbital debris." In

striking contrast to the results for the

leading edge cells, it appears that the

majority of trailing edge impacts are

produced by cosmic dust particles.

G LDEF (trailing edge) ° LDEF (covered trailing edge) C

0

0

°

oop - ate°`°

a ° o^D`^p

ractionation

Trend

0 O IDPs

0 Chondrite

10 -3

10-2

10-1

100 101 102

Fe/Mg

525
impacts determined in laboratory, simulation experiments. The Al/Mg, Ca/Mg and Ti/Mg ratios of most

trailing edge impacts actually deviate from the chondritic composition in the expected directions but, as

already mentioned, the deviations are much larger than the fractionation seen in the laboratory

experiments. We consider such large fractionations to be the likely result of the higher velocities of the

LDEF impacts. As a working criterion for distinguishing between cosmic dust and man-made debris,

we classify impacts that plot inside a region bounded by lines a factor of 10 above and below the

fractionation trend extrapolated from laboratory experiments as being of likely interplanetary dust

origin. Impacts that plot outside this region are classified as being of possibly man-made debris origin.

In Figs. 12a and 12b all impacts except two plot inside of the region while in Fig. 12c, 7 plot outside.

A tentative classification of all impacts analyzed by SIMS is thus as follows (Table 2): nine of 11

leading edge impacts are of man-made origin, the origin of two impacts without projectile material

cannot be identified. In contrast, 45 of 58 impacts on the trailing edge are of probably natural origin,

two of them probably from FeS particles, 43 from particles with compositions similar to those of

chondrites, whereas 12 impacts are possibly caused by man-made debris. It should be pointed out,

however, that the identification of man-made debris is much more certain for the leading edge impacts

than those from the trailing edge. The former have compositions (only Al, Ti) that are expected for

debris while the debris classification for the trailing edge is mostly by default; only one impact (mostly

Fe and Al) can reasonably be associated with an expected terrestrial composition and there are no

impacts with Al only on the trailing edge. Thus, most of those classified as possibly man-made debris

may, in fact, be cosmic particles.

Table 2. Identification of Projectile Material

Leading edge Trailing edge

Micro- Debris Unid. Micro- Debris Unid.

meteoroids meteoroids

No enhancements _ _ 2 - 1

Enhancement in single element - 8 (Al) - 2 (Fe)

Enhancement in several - 1(Ti) - 43 12 (poss.) -

elements

Total 0 9 2 45 12 (Poss.) 1

526
SUMMARY AND CONCLUSIONS

1. The basic capture cell design worked successfully. As long as the entrance foils stayed in place

projectile particles produced "extended impacts" that could be successfully analyzed by ion probe

mass spectrometry.

2. All of the entrance foils on the leading edge and 90% of those on the trailing edge failed during

flight. However, the statistics of single craters and extended impacts show that many foils on both

edges lasted for a considerable period. Thus, analysis of "extended impacts" on both the leading

and trailing edges was possible.

3. Analysis of leading edge impacts shows that at least 9 of I I impacts studied are produced by manmade debris (the remaining two did not yield any elemental enhancements due to projectile

material).

4. In contrast, the analysis of the impacts on the trailing edge area shows that 45 out of 58 are of

probably natural origin. The identification of the remainder is uncertain but they are possibly due

to orbital debris. However, no unambiguous example of a space debris impact was found on the

trailing edge.

5. Most extended impacts have compositions that differ markedly from those measured for IDPs

collected in the stratosphere. The differences are consistent with volatile/refractory element

fractionation affecting particles with cosmic compositions. This effect had previously been seen

by us in simulation experiments of hypervelocity impacts, but is more pronounced in the LDEF

data, probably due to the high velocities of the impactors. Elemental fractionation in the impact

process itself represents the largest single impediment to accurate measurements of projectile

chemistry.

6. Contamination of initially clean Ge surfaces during exposure in space was also found to be a

significant effect limiting the ability to make accurate measurements of projectile chemistry. The

source of the Si seems to be outgassing from RTV, but other sources, contributing elements such

as Mg and Al, are still unknown.

Because leading and trailing edge entrance foils failed at comparable rates, the major causative

failure factors must be similar. While atomic oxygen erosion contributed to a somewhat higher

failure rate on leading edge cells, it cannot be the major cause of failure. We suspect that UV

embrittlement coupled with thermal cycling is responsible for most of the foil degradation.

Future work will concentrate on the analysis of more leading edge impacts and the development of

new techniques for measuring elemental abundances in extended impacts.

527
REFERENCES

Amari, S.; Foote, J.; Simon, C.; Swan, P.; Walker, R.; Zinner, E.; Jessberger, E. K.; Lange, G.; and

Stadermann, F. J.: SIMS chemical analysis of extended impact features from the trailing edge

portion of LDEF experiment AO187-2. LDEF - 69 Months in Space, NASA CP-3134, part 1; 1991,

pp. 503-516.

2. Zook, H. A.: Asteroidal versus cometary meteoroid impacts on the Long Duration Exposure

Facility (LDEF). Second LDEF Post-Retrieval Symposium, NASA CP-3194, 1993.

3. Mulholland, J. D.; Simon, C. G.; Cooke, W. J.; Oliver, J. P.; and Misra, V.: Long-term particle flux

variability indicated by comparison of interplanetary dust experiment (IDE) timed impacts for

LDEF's first year in orbit with impact data for the entire 5.75-year orbital lifetime. Second LDEF

Post-Retrieval Symposium, NASA CP-3194, 1993.

4. Stadermann, F.: Rare earth and trace element abundances in individual IDPs. Lunar Planet.

Sci. XXII, 1991, pp. 1311-1312.

5. Stadermann, F.: Messung von Isotopen- and Elementhaufigkeiten in einzelnen interplanetaren

Staubteilchen mittels Sekundarionen-Massenspektrometrie. Ph.D. Thesis, University of Heidelberg,

Germany, 1990.

6. Lange, G.: Quantitative Multielementanalyse von Einschlagsruckstanden auf LDEFStaubdetektoren. Ph.D. Thesis, University of Heidelberg, Germany, 1986.

7. Brownlee, D. E.; Tomandl, D. A.; and Olszewski, E.: Interplanetary dust; a new source of

extraterrestrial material for laboratory studies. Proc. 13th Lunar Planet. Sci. Conf., 1977,

pp. 149-160.

8. Brownlee, D. E.; Horz, F.; and Bradley, J.: Interplanetary meteoroid debris in LDEF metal craters.

Second LDEF Post-Retrieval Symposium, NASA CP-3194, 1993.

528
SIMS CHEMICAL AND ISOTOPIC ANALYSIS OF IMPACT FEATURES

FROM LDEF EXPERIMENTS AO187-1 AND AO187-2

Frank J. Stadermann

Technical University Darmstadt, Material Science Department

Hilpertstr. 31, Geb. H, D-64295 Darmstadt, Germany

Phone: (+49) 6151-813223, Fax: (+49) 6151-813222

Sachiko Amari, John Foote, Pat Swan, Robert M. Walker, Ernst Zinner

McDonnell Center for the Space Sciences and Physics Department

Washington University, St. Louis, MO 63130, USA

Phone: 314-935 6257, Fax: 314-935 4083

SUMMARY

Previous secondary ion mass spectrometry (SIMS) studies of extended impact features from

LDEF capture cell experiment AO187-2 showed that it is possible to distinguish natural and manmade particle impacts based on the chemical composition of projectile residues. The same

measurement technique has now been applied to specially prepared gold target impacts from

experiment AO 187-1 in order to identify the origins of projectiles that left deposits too thin to be

analyzed by conventional energy-dispersive x-ray (EDX) spectroscopy. The results indicate that

SIMS may be the method of choice for the analysis of impact deposits on a variety of sample

surfaces. SIMS was also used to determine the isotopic compositions of impact residues from

several natural projectiles. Within the precision of the measurements all analyzed residues show

isotopically normal compositions.

INTRODUCTION

Among the most noticeable effects of the space environment on spacecraft are impacts

produced by the bombardment with small particles from various sources. Several experiments on

board the Long Duration Exposure Facility (LDEF) satellite dealt with the analysis of impact craters

and projectile debris. There are two basic objectives for such experiments. One is the study of

^. r,^ Rp w < z+fl^ 3

^? z^n rye t^ k^a

461
micrometeoroids in order to determine the flux of interplanetary particles in space and to learn

about their nature and origin. The other is the assessment of possible hazards to space flight posed

by such impacts. For this purpose it is important to determine (a) the absolute number of impacts

and (b) the ratio of natural (micrometeoroids) to man-made (orbital debris) impact particles.

Various attempts have been made to estimate this ratio, e.g., by comparing particle fluxes on

differently oriented LDEF surfaces. However, a more direct approach to this problem is based on

the chemical characterization of particle residues. Since micrometeoroids and orbital debris particles

have distinct chemical properties, it is possible to determine the relative contribution of either type

to the total particle flux by analyzing the composition of impact debris on LDEF surfaces.

Although all outer surfaces of the LDEF satellite are covered by impact features of various

types and sizes, only few are suited for micro-chemical analysis. What can usually be seen on

space exposed materials are only the effects of hypervelocity impacts, such as craters, dents, and

cracks, but not remnants of the impacting particle. Due to the high velocities of impacts (typically

several km/sec), practically no projectile material survives the collisions unaltered and only rarely

chunks of projectile material can be found within or in the vicinity of impact craters that are large

enough for energy dispersive x-ray analysis (EDX) . However, frequently there is a thin layer of

debris around impact features where some fraction of the particle material re-condensed after being

vaporized during impact. This layer of debris is generally too thin to be seen in either optical or

scanning electron microscopes (SEM), but secondary ion mass spectrometry (SIMS) can often be

used to analyze this material even when its thickness is only a few atomic monolayers.

impacting particle

^Au-Pd coat (1 o0 A)

—plastic foil (2,5 pm)

^ Ta coat 0 300 A)

0.2 mm \ i i ejecta

—Ge target

Figure 1. Schematic of capture cell experiment A0187-2.

In principle, impacts on all kinds of surfaces can be analyzed to determine the nature of the

projectile material. In practice, however, most accurate analytical results can be achieved from

impacts on clean substrates and with relatively large amounts of deposited debris. These conditions

are satisfied in the capture cell experiment AO 187-2, which was specifically designed for this kind

of investigation. The principle of that experiment is shown in Figure 1. A target plate of highpurity germanium is covered with a thin foil separated by a small distance. A high velocity particle

of sufficient size penetrates the foil and may be disrupted in the process, spreading out into a debris
shower. This shower impacts the target plate and is further disrupted, melted and vaporized. Some

of the projectile material is retained in the impact region on the germanium plate. The projectile

material ejected from the impact zone is collected on the backside of the foil and on the surrounding

area of the germanium plate. Since only a small amount of material can escape through the impact

hole in the cover foil, most impact debris stays in the capture cell and can be analyzed after the cell

has been disassembled.

with an O— primary beam of 1-2 nA that was

rastered over an area of 40 μm x 40 μm. The

width of individual steps was chosen between 35

and 60 gm each. Since each measurement

consisted of up to 50 steps, these traverses had a

typical length of several hundred μm and width

of about 40 μm. The secondary ion signals of

the elements O, Mg, Al, Si, Ca, Ti, Fe, Ni, Ge,

and Ta were monitored during the scans. These

o ioo zoo 300 aoo soo 600 700 elements were chosen because they are the most

Distance (gm) abundant elements in cosmic dust particles and/or

in the capture cells themselves. Typical results

Figure 2. Secondary ion signals of different from one of these scans are shown in Fig. 2. The

elements in a traverse across an impact increase in secondary ion signals near the center

feature on a Ge plate. The center of the of the impact can clearly be correlated with

impact is located near the 200 μm distance impact deposits.

mark.

To date more than 60 extended impacts on

germanium plates from experiment AO187-2 have been analyzed by SIMS for the chemical

composition of the projectiles. Ion signals associated with material from the impacts could be

detected in almost all analyzed impact areas despite serious problems with contamination. It was

possible to discern the most likely origins of the projectiles by comparing the compositions of the

deposits to those of cosmic dust particles and well known types of man-made debris. Thus we

could show that at least 75% of the impacts on the trailing edge of LDEF were caused by

micrometeoroids while virtually all analyzed impacts on the leading edge were caused by manmade debris particles (ref. 2).

In our previous studies analyses were focused on samples from capture cell experiment

AO187-2 (refs. 1, 2). Because most foils did not survive the 51 /2 years of exposure in space, we

analyzed extended impact features on the germanium plates, produced by projectiles which had

arrived while the plastic foils were still in place. First, several different types of extended impact

features were identified during optical and SEM analyses. The chemical compositions of the

deposits were then determined by SIMS step

scans across the impact features. At each step the

Impact no. E03-2-19C-1 composition of the surface layer was measured

N

C

a

0

U
After having established that SIMS is a useful analytical technique for the determination of

the chemical composition of thin layers of impact deposits on the germanium capture cells, we

undertook an investigation of its applicability to the analysis of impacts on other LDEF surfaces.

We also used SIMS for the measurement of the isotopic compositions of certain impact debris

fragments. Such measurements have not yet been possible on thin deposition layers on the

germanium plates of the capture cells due to the thinness of the layers which causes the signal at a

given isotopic mass to change rapidly with time.

CHEMICAL ANALYSIS OF GOLD TARGETS FROM EXPERIMENT A0187-1

Next to samples from the capture cell experiment, impacts on witness plates of high-purity

Au from experiment A0187-1 appeared particularly interesting because debris analyses on these

surfaces had already been performed by conventional

SEM-EDX techniques (ref. 3). Unfortunately, in more

than 50% of all Au impacts studied no detectable EDX

Impact residue signals could be found, obviously complicating the

\•^ • statistical interpretation of the data. We tried to improve

this situation analyzin g ese u sa these A mmples with eth

sam Se SIMS analysise technique that w had u d used earlier

tX.: , g t ....: :::::::.:.::::.:::.::.:.::.:.:.:::.::::. on the Ge impacts. For a preliminary investigation Fred

Horz generously provided us with 15 Au samples that

had previously been studied by SEM-EDX (ref. 3).

Eleven of those impact projectiles had been classified as

Quartz Plate "natural", one as "man-made" and the origins of the

i i i i i i i i i i i i i i i other three were still unknown.

.... ...::.:::..

Figure 3: Steps in the sample

preparation of Au targets from LDEF.

SIMS measurements of the Au impacts posed

some analytical Y pProblems. The impact craters in the Au Pact c e s

foil areenerall relatively deep and are surrounded g Y Y P e urro ded bY

a "lip" of Au that rises above the original sample

surface. Since SIMS requires a flat sample surface it

was necessary to develop a new sample preparation

technique for the analysis of these kinds of impact

craters (Fig. 3). Preliminary studies had shown that the

most interesting areas to analyze in the Au samples are

impact residues located inside the crater and on the lip.

In order to flatten the lip a quartz plate was pressed

onto the sample surface. After the surface was even, a

needle was carefully pressed against the underside of

the thin Au sheet to push the bottom of the crater up.

The entire procedure was monitored under a
0 100 200 300 400 500

Distance (μm)

Figure 4: Secondary ion count rates from a SIMS

scan across A0187-1 impact "Au89".

Au89

—0--16 o+

—`— 24MB

—L3 27Ai+

0 285i+

t 40Ca+

_ 48 Ti+

56 Fe+

^— 60Ni+

—0— 63Cu+

—1 197Au

1

1

rn1

O

O

U1

1

108

107

106

ZO

U 105

104

103

102

Au72

-- 0-16o+

--a— 27Ai+

--0 28Si+

i

--0 40Ca+

—^ — 4sTi+

56Fe+

--u— 60Ni+

— 0— 63Cu+

--;— 197Au+

stereomicroscope through the quartz disk. That way the surfaces from inside the crater walls

became accessible to SIMS measurements on a flat surface. After these preparations, the SIMS

scanning technique was applied to the Au witness plates.

The SIMS scans of these "highpurity" Au substrates revealed high

levels of contamination that cannot be

attributed either to the impacts

themselves or to contamination

originating from the LDEF spacecraft

(see Figs. 4-6). Instead, it appears that

the Au target itself contains significant

amounts of trace contaminants. In spite

of this problem, which led to generally

higher background-level in most of the

measurements, it was indeed possible

to determine the origin of the projectiles

in several of the Au target impacts. To

date SIMS scans have been made

across seven flattened craters from

experiment A0187-1. Examples of the

results are shown in Figures 4-6.

Impact "Au89" (Fig. 4) had

originally been classified as "natural"

based on the EDX analysis of small

chunks of debris that had been found in

the crater. The SIMS scan shows a

complex pattern with several elements

—such as Al, Fe, Ca, and Mg— clearly

enriched in the vicinity of the crater

whose center is located near the 200 pm

distance mark. An elemental signature

like this is typical for a natural particle

(micrometeoroid). The. EDX

classification of this impact can

therefore be confirmed.

0 100 200 300 400 500

Distance (μm)

Figure 5: Secondary ion count rates from a SIMS

scan across A0187-1 impact 'Au72 ".

Figure 5 shows data from a scan

across impact "Au72" that was

classified as "man-made" before. Here

too, that classification could be

confirmed by the SIMS measurements.
10

1

0 100 200 300 400- 500 600 700

Distance (μm)

Figure 6: Secondary ion count rates from a SIMS

scan across A0187-1 impact "Au79".

Au79

---0-160+

—0 24Mg

—0 27Ai+

—0 28Si+

—a— 40C&

—O — 48 Ti+

+ 56Fe+

—v- 60 Ni+

- 6^— 63 Ce

I 197 A.

r

Zr- - "'a

.^ 1

0

U1

The most enriched element at the center

of the crater (near the 120 μm mark) is

Al, accompanied only by a smaller

enrichment of Si. Such a prominent Alrich composition is highly indicative of

an aluminum-oxide particle from rocket

exhausts.

The origin of the projectile that

caused impact "Au79" was unknown

because no debris could be found in the

SEM-EDX study that was large enough

for a determination of the chemical

composition. Here the strength of

SIMS as a highly-sensitive microanalytical technique becomes obvious

(Fig. 6). Only aluminum is significantly

enriched near the position of the crater

at the 240 μm distance mark. This

impact can unambiguously be classified

as "man-made".

The SIMS measurements did not always allow the identification of hitherto unknown

projectiles, but the total number of "unknowns" was reduced. It appears that SIMS is the method

of choice for the analysis' of impact debris on various surfaces, provided the samples can be

suitably prepared for SIMS analysis.

In an effort to characterize the chemical composition of some of the "natural" impact

projectiles on the Au target plates in more detail, we measured the relative abundances of 24

elements in two chunks of debris from the impacts "Au104" and Au280". The results of these

measurements are shown in Figures 7 and 8, together with values of the meteoritic abundances of

C1 chondrites. These Cl-abundances are well known from the study of meteorites (ref.4) and

there is reason to expect that natural projectiles, i.e., micrometeoroids, have compositions that are

similar to those of Cl chondrites (ref. 5). Since only relative abundances can be measured with

SIMS, all elements are normalized to Si, whose concentration was arbitrarily set to its C1-

abundance.

Since two fragments were analyzed from each impact an. upper limit of the precision of the

measurement can be estimated from the variation between both measurement runs (inherent

heterogeneities in the sample would lead to even bigger variations between the two measurements).

The precision appears to be quite good for the majority of the elements. However, the accuracy of

the determinations is not as good, possibly due to the inherent problems of quantification in the

SIMS technique. Still, the similarity between the compositions of the projectiles and the C1-

abundances is striking. Since all elemental abundances are normalized to Si, an over-abundance of
II^II1'J[!IIII IL

this element would lead to seemingly lower abundances of the other elements. Interestingly, in

impact "Au280" Ca is depleted while in impact "Aul04" Fe, Co, and Ni concentrations are lower

than the Cl-abundances. Both observations agree with earlier measurements of certain cosmic dust

particles that were collected in the stratosphere (ref. 5). Clearly, this determination of the

abundances of 24 elements leaves no doubt about the natural origin of the particles that caused

these impacts.

106 

Composition of Deposits from LDEF A0187-1 Impact "Au104"

• Measurement 1

105

....... ..... ...........................::::>:.... .

O' ® O Measurement 2

E 104 .....,.,,, ........... ............. _................. Cl Abundances

o103 .... 0 ............::>::...

102 .................. 0..

U0

1 01 ........................

100 ...............................

10 Li NaMgAl Si K Ca Sc Ti V CrMnFe Co Ni CuZn Rb Sr Y Zr CdBa Ce

Figure 7: Elemental abundances of two fragments normalized to a

condritic Si.value and compared to C1-abundances.

106 

Composition of Deposits from LDEF A0187-1 Impact "Au280"

"' • Measurement 1 105:::::> :::::<.. .:...

O' O Measurement 2

:.::.:. :::... a 104 ... .... ...:::.^..... '''`" Cl Abundances

0 103 - . - . • ..........Q.• ................ ..... O ... . .. .

102 :::.:::.:..... :..

o

U loQ lt l­......................... ,r:...................................... s:........... n ...

100-

........ ............ ........ ...

• e

10-L

Li Na Mg Al Si K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Rb Sr Y Zr Cd Ba Ce

Figure 8: Elemental abundances of two fragments normalized to a

chondritic Si value and compared to CI -abundances.
8 13C (in %o) 815N

-1

terrestrial range

Figure 9: Average C and N isotopic

compositions of impact residue from

"A004" and "Au280" and values of IDPs

for comparison.

ISOTOPIC MEASUREMENTS IN IMPACTS FROM A0187-1 AND A0187 -2

We were also able to perform the first isotopic measurements of impact debris on LDEF.

Isotopic analysis of LDEF impacts was one of the original objectives of experiment A0187-2. The

isotopic composition of projectile material is of special interest since natural particles

(micrometeoroids) are found to have isotopic compositions that sometimes are very different from

normal, terrestrial values (refs. 6, 7). If similar anomalies could be found in impact debris that

would be one more piece of evidence for an extraterrestrial origin of the projectile material.

Moreover, the LDEF impacts represent a different, and possibly isotopically distinct, sampling of

the total infall of extraterrestrial material than do micrometeorites recovered in the stratosphere. The

results of the isotopic measurements are given here in the 5-notation, which denotes the deviation

of the measured isotopic ratio from the normal ratio (i.e., the ratio of a terrestrial standard) in

permil (%o). Example: If a measured 15NI14N ratio were 5% higher than normal, the corresponding

5-value would be 515N = 50%o. Small variations of the isotopic compositions can also be observed

in terrestrial material. Therefore all results have to be compared to the maximum observed range of

isotopic compositions in terrestrial material and only an object with isotopic compositions clearly

outside of that range can unequivocally be classified as extraterrestrial. On the other hand, a normal

isotopic composition does not necessarily imply a terrestrial origin.

From the Au-foils from LDEF experiment

A0187-1 we selected impacts Au 104 and Au280

because both have large amounts of apparent

projectile residues and both had been classified as

"natural" according to the EDX analyses. As

shown above, this classification was confirmed

by the SIMS measurements of major and trace

elements.

In Figure 9 the C and N isotopic

compositions of impact residues are compared to

the values measured in interplanetary dust

particles (IDPs) collected in the stratosphere (ref.

7) and to the range of ratios found in terrestrial

samples. Although both projectiles are clearly of

natural origin their C and N isotopic

compositions are close to normal. This is not

very surprising since only one third of all

analyzed IDPs show isotopic anomalies in N and

none show anomalies in C. The particle "Santa

Fe" which is shown for reference has the largest

N anomaly among all measured particles of that

kind.
20

10

0

s°

0

o -10

-20

30

...

Al.

solar

IN

O 104

n 280

C IDPs

-40 -30 -20 -10 0 10 20 30

826Mg ( %o)

Figure 10: Three-isotope-plot of the Mg isotopic compositions of

impact deposits from two AO187-1 impacts and those of

Interplanetary Dust Particles (IDPs). The errors shown are I a.

Figures 10 and 11 show the Mg and Si isotopic compositions of impact debris from

AO187-1 impacts "Au104" and "Au280" in three-isotope-plots. The isotopic compositions of

elements with 3 stable isotopes are usually displayed in this way. The 825Mg and the 826Mg values

refer to the 25Mg/24Mg ratio and the 26Mg/24Mg ratio, respectively (29Si/28Si and 30Si/28Si for

silicon). The normal isotopic compositions are denoted "Solar" in the diagrams. Small linear massdependent isotopic fractionations —which occur frequently, even in the terrestrial environment—

would lead to isotopic compositions that are shifted from the "Solar" composition along a slope1 /2-line in a three-isotope-plot. This line is denoted "Fractionation line" in the diagrams. Any

isotopic composition that differs only little from the "Solar" composition and that plots on that line

is considered terrestrial while composition that are clearly off that line are indicative of an

extraterrestrial origin. As can be seen, the measured impact debris has isotopic compositions of Si

and Mg that are essentially terrestrial. The degree of Mg fractionation is also much smaller than the

range observed in IDPs collected in the stratosphere, whose compositions are shown for

comparison.
20

10

0

-10

N

-20

-110

S olar

60, O 104

^Ia^^' n 280

IDPs

-40 -30 -20 -10 0 10 20

830Si ( %o)

Figure 11: Three-isotope-plot of the Si isotopic compositions of

impact deposit and those of Interplanetary Dust Particles (IDPs).

The errors shown are l6

Unfortunately, the isotopic analysis of projectile material in extended impacts on germanium

plates from experiment AO187-2 is extremely difficult. The reason is the thinness of the impact

deposits. An exception is impact CO2-2-17C-1, where several solid fragments were found on the

rim of the impact feature. The results of the Mg and Si isotopic analysis of these fragments are

shown in Figures 12, 13, and Table 1. The isotopic compositions of the fragments plot close to the

terrestrial values. Here too, the measured isotopic compositions do not have an identifiably

extraterrestrial signature.

825Mg (%o) 826Mg (%o) 829Si (%o) 830Si (%o)

Fragment a 30 ± 13 17 ± 9 -2 ± 14 6 ± 21

Fragment b 13 ± 12 13 ± 9 -6 ± 13 14 ± 17

Fragment c -2 ± 10 -10 ± 10 -14 ± 13 -16 ± 16

Fragment d -1 ± 7 28 ± 10 9 ± 12 -11 ± 12

Fragment e 10 ± 11 -7 ± 12 -8 ± 14 27 ± 17

Fragment -24 ± 8 -6 ± 8 3 ± 10 7 ± 9

Table 1. Results of the Mg and Si isotopic measurements of

individual fragments on the rim of impact CO2-2-17C-1. The errors

are 1 a.
40

30

^-. 20

10

`-^ 0

^04., -10

-20

t`VO -30

-40

-50

o Individual Fragments on

the Rim of CO2-2-17C-1

n Thin deposit of

impact CO2-1 -11G 1

► 4 C-2

n

n

-100 -80 -60 -40 -20 0 20 40 60 80

826Mg (%0)

Figure 12. Three-isotope-plot of the results of the Mg isotopic

measurements of fragments on the rim of impact CO2-2-17C-1 and

of deposits in the extended impact CO2-1-14C-2. The errors shown

are 1 wand the diagonal line is the Terrestrial Fractionation Line.

o Individual Fragments on

10 , the Rim of CO2-2-17C-1

o

n Thin deposit of

S° _ 10. impact CO2-1-11G I

^,,,^ 14C-2

-30

-50.^^n

-70

-140 -120 -100 -80 -60 -40 -20 0 20 40 60

830Si (%0)

Figure 13. Three-isotope-plot of the results of the Si isotopic

measurements of fragments on the rim of impact CO2-2-17C-1 and

of deposits in the extended impact CO2-1-14C-2. The errors shown

are 1 a and the diagonal line is the Terrestrial Fractionation Line.
Impact CO2-2-17C-1 was the only case of an extended impact from experiment AO187-2 in

which we found projectile fragments that had apparently survived the impact. In contrast to the

isotopic analyses of these fragments are the analyses of a thin debris layer from impact CO2-1-14C2 (Figures 12 and 13). Here both the Mg and Si isotopic data show large negative (shifts to the

lower left, i.e. toward more negative 5-values) mass fractionation effects; in addition, the Si data

show substantial deviations from the terrestrial mass fractionation line.

A more detailed analysis of these data revealed that these large fractionations and the

deviations from the fractionation line are not genuine isotopic effects in the measured material but

are artifacts resulting from the small thickness of the impact deposits. Because the layer of

deposited projectile is sputtered away during SIMS analysis, the secondary ion signal from a thin

layer is not constant but decreases rapidly as a function of time. Since the isotopes of Mg and Si

are measured in sequence, the non-linear nature of this decrease can produce the effects shown by

the CO2-1-14C-2 data. High throughput (large magnet), multiple collector SIMS instruments

capable of accurate isotopic measurements are currently being developed for the study of

extraterrestrial materials (K. McKeegan, UCLA, private communication). Such instruments may

have the required sensitivity and measurement capabilities to permit isotopic measurements of very

thin impact deposits.

The extended impacts of LDEF experiment A0187-2 that have already been partially studied

by existing SIMS techniques represent an extremely important scientific resource for future work.

In particular, some of these impacts may make it possible to measure the isotopic composition of

cometary material. Dust particles from long-period comets encounter the earth with very high

velocities and are thus preferentially destroyed relative to slower, asteroidal particles during

atmospheric entry (ref. 8). Cometary particles may thus be grossly under-represented in the

stratospheric micrometeoroid collections. In contrast, high velocity particles produce extended

impacts with high efficiency and should thus be well represented in the existing collection of

capture cell impacts.

Because of their potential scientific importance, continued care should betaken to store the

relevant surfaces of experiment AO187-2 under clean conditions so they may be properly analyzed

by future, improved analytical instirurnents.
REFERENCES

1. Amari S., Foote L. Simon C., Swan P., Walker R.M., Zinner E., Jessberger E.K., Lange

G., and Stadermann F.J.: SIMS chemical analysis of extended impact features from the

trailing edge portion of experiment A0187-2. Proceedings of First LDEF Post-Retrieval

Symposium, NASA CP 3134, 503-516, 1991.

2. Amari S., Foote J., Swan P., Walker R.M., Zinner E., and Lange G.: SIMS chemical

analysis of extended impacts on the leading and trailing edges of LDEF experiment

A0187-2. Proceedings of Second LDEF Post-Retrieval Symposium, NASA CP 3194,

513-528, 1993.

3. Bernhard R.P., See T.H., and Horz F.: Projectile composition and modal frequencies on the

"Chemistry of Micrometeoroids" LDEF experiment. Proceedings of Second LDEF

Post-Retrieval Symposium, NASA CP 3194, 551-573, 1993.

4. Anders E. and Grevesse N.: Abundances of the elements: Meteoritic and solar. Geochimica

et Cosmochimica Acta, 53, 197-214, 1989.

5. Stadermann F. J.: Rare earth and trace element abundances in individual IDPs. Lunar and

Planetary Science, XXII, 1311-1312, 1991.

6. McKeegan K. D.: Ion microprobe measurements of H, C, O, Mg, and Si isotopic

abundances in individual interplanetary dust particles. Ph. D. Thesis, Washington

University, St. Louis, 187 pp, 1987.

7. Stadermann F. J., Walker R. M., and Zinner E.: Ion microprobe measurements of nitrogen

and carbon isotopic variations in individual IDPs. Meteoritics, 24, 327, 1989.

8. Flynn G. J.: Atmospheric entry heating: a criterion to distinguish between asteroidal and

cometary sources of interplanetary dust. Icarus 77, 287-310, 1989.
o Spinel-chromite-TiO,

e Hibonite

_prR,v 

^ltrv.. aY

^,l UALITY 2 4ft^:,^^slslrvGA 9C6 f2 #^YaNm2> ^.ue^A6 F.^Z ^c ^^ G ^.a^^ •^^, •^1^.1

347-424(1990)

Society, 1990. Printed in USA

Abstracts of the 53rd Meeting of the Meteoritical Society

Perth, Western Australia, 17-21 September 1990

probe studies of SiC from different chondrite groups. C. M. O'D.

lexander,' C. Prombo,' R. M. Walker,' E. Zinner' and J. W. Arden.'

dcDonnell Center for the Space Sciences, Washington University,

GLouis, MO 63130, USA. 'Dept. Earth Sciences, Oxford University,

ifordOXI 3PR, UK.

[ere we give new results from our continuing survey of SiC it) prim-

; meteorites. Previously we reported C and Si isotopic data for SiC

ns in acid residues of the UOCs Krymka and Inman (1) that indict differences exist in the isotopic composition of SiC both within

ordinary chondrites and between the CMs and UOCs. Subsequently

have analysed a further four UOCs (Tieschitz, Bishunpur, Chainpur

Semarkona) as well as the CV3 chondrite Leoville.

t Murchison the Si isotopic compositions are arrayed along a slope

dine and seem to cluster into four groups that are delineated in Figs.

ad 2. In terms of their Si isotopes the grains in Bishunpur and

tinpur(Fig. 1) show a similar spread in values as in Murchison but

apparent clustering. In contrast, the anomalous grains in Semarkona

(Tieschitz show a more restricted range of Si compositions than in

Ingeneral, the range of C isotopic compositions in UOC SiCs is similar

that in Murchison but with different distributions. For instance, in

Wnpur the C isotopes are, on average, more 13C enriched than in

nrchison with 12 of the 36 grains analysed so far having a' 3C >_ 100006

cipared with only 10 out of 89 grains in Murchison. On the other

md, in Bishunpur, as is the case for the Si isotopes, the carbon isotopes

ow a similar distribution as in Murchison.

np. 1 Ch.J.pu, (LJ.L3) Fle. 3 Le Hle (CVs)

zi

,Ti so b

p N-1

so o so loo`

a 70 si (%.) 6 3o si (Y.)

30

10

-10

-30 /

-50 /

-70

-70 -50 -30 -10 10 30 50

818 OsMow

In four of the seven meteorites studied some fraction of the SiC grains

is isotopically normal. Leoville (Fig. 2) seems to contain the greatest

proportion of this 'normal' SiC; indeed, we have found only 2 isotopically anomalous grains out of 20 analysed. The normal isotopic compositions suggest these grains may have formed within the solar system.

However, at present we cannot rule out the possibility of terrestrial

contamination. Experiments are in progress to resolve this issue.

Our results reinforce the evidence for both intragroup and intergroup

variations of the isotopic composition of SiC in primitive meteorites.

However, it remains to be determined whether this is due to differences

in sample preparation, nebular processing, or nebular heterogeneity.

Reference: (1) Alexander et aL (1990) LPSC 21, 9-10.

Oxygen isotopic compositions of oxide grains in Semarkona. C. M. O'D.

Alexander,' E. Zinner' and J. W Arden.' 'McDonnell Center for the

Space Sciences, Washington University, St. Louis, MO 63130, USA.

'Dept. Earth Sciences, Oxford University, Oxford OX 3PR, UK.

Oxygen is unique amongst the major rock-forming elements in exhibiting in a large size range of objects isotopic anomalies that cannot

be explained in terms of mass fractionation or radioactive decay. In

chondrites these variations are thought to result from exchange between

isotopically distinct gas and solid (or liquid) reservoirs. For instance, it

appears that refractory inclusions in carbonaceous chondrites were initially very 160-rich and that subsequently the minerals in them exchanged, to a greater or lesser extent, with a gaseous reservoir which

had an isotopic composition that lay close to the terrestrial fractionation

line (1). Allende chondrules show evidence for a similar exchange (2).

In the ordinary chondrites chondrules also show evidence for isotopic

exchange (2, 3) but in their case it seems that, while the gaseous reservoir

was similar to that in the carbonaceous chondrites, the solid material

was 11 0-depleted (3). However, this model appears inconsistent with

the positive 'correlation' between the degree of 16 0-depletion in the bulk

meteorite and oxidation state, since presumably the most oxidised meteorites have experienced the greatest degree of exchange with the gas.

In an attempt to elucidate the nature of the oxygen reservoirs sampled

by ordinary chondrite material we have analysed the oxygen isotopic

composition of acid resistant mineral grains (that included spine], chromite, TiO, and hibonite) from a Semarkona residue (Fig.). Despite the

scatter in the data and with the exception of two hibonite grains the

minerals plot near the composition of the putative gaseous reservoir

rather than the 16 0-depleted solid reservoir. Large Cr-spinel grains from

the Murchison matrix have, within the accuracy of our technique, identical isotopic compositions (4).

The composition of the hibonites are as extreme as those from carbonaceous chondrites (5, 6). It is as yet uncertain whether refractory

inclusions in ordinary and carbonaceous chondrites share a common

source. Nevertheless, it appears that the precursor materials had similar

oxygen isotopic compositions. In the carbonaceous chondrites the bulk

of the solid material is also thought to have been initially 16 0-rich. It

is, therefore, puzzling that the bulk of the ordinary chondrite material

was 160-depleted. References: (1) Clayton et aL (1977) EPSL 34, 209-

224. (2) Clayton et al. (1983) In Chondrules and Their Origins, pp. 37-

43. (3) Clayton et aL (1983) Meteoritics 18, 282. (4) Grossman et al.

(1988) LPS 19, 435. (5) Fahey et aL (1987) Ap. J. 323, L91. (6) Ireland

and Zinner (1989) Meteoritics 24, 279.

Micrometeoroid experiment on the long duration exposure facility. S.

Amari,' J. Foote,' C. Simon,' P. Swan,' R. Walker,' E. Zinner' and

E. K. Jessberger.' 'McDonnell Center for the Space Sciences and

Physics Department, Washington University, St. Louis, MO 63130,

USA. 'Max- Planck- Institut fiir Kernphysik, Heidelberg, W. Germany.

The Long Duration Exposure Facility (LDEF) was returned to earth

in January after 5.8 yr in space. Experiment A0187-2 consisted of 237

"capture cells" (total area 2.1 m2), each consisting of polished Ge plates

347
348 Abstracts

separated by 200 um from thin (2 um) mylar "entrance" foils coated

on one side with 1000 A of Ta and on the other with 100 A of Au-Pd.

Half of the cells were mounted on the leading edge (facing forward

direction) of LDEF and the rest on the trailing edge. Laboratory impact

experiments have demonstrated that debris and vapor deposits from

impacts can be collected and analyzed by ion probe techniques on both

the plastic foil and the Ge plate (1, 2). For unknown reasons, most of

the plastic foils failed during Right; however, 12 cells on the trailing

edge are intact. Numerous impacts, ranging in size from those that are

visible to the naked eye to submicroscopic, are found on both the leading

and trailing edges. Preliminary SEM scanning of one plate on the leading

edge at 300x gives a density of -60 cm 2 for craters > 1 to 2 um in size.

The crater density is much lower on the trailing edge due to the differences in the average velocities of impacting particles caused by the

orbital motion of LDEF. Impact craters on the trailing edge surfaces

are also distinctly different than those on the leading edge, being more

subdued and in some cases containing an abundance of Ta fragments.

Three types of impacts are found on the Ge: 1) craters with "jagged"

morphologies reflecting the brittle nature of Ge, 2) "spider webs" consisting of myriads of small craters arranged in complex patterns (3), and

3) features consisting of one or more larger craters in a spray of smaller

craters. Type 2 and 3 features are produced by impactors that have

undergone varying degrees of disruption in traversing the entrance foils.

Their prevalence demonstrates that the plastic foils remained intact for

considerable periods of time, even on the leading edge. Also seen are

circular features with dendritic crystals in the center, probably caused

by very low velocity impacts of partially liquid droplets of human, not

cosmic, origin. Results of the initial analysis of a representative set of

impacts will be presented at the meeting. References: (1) Jessberger E.,

Kuczera H., Lange G., Sutton S. and Zinner E. (1985) LPSC 16, 400-

401. (2) Lange G., Eigner S., Igenbergs E., Jessberger E. K., Kuczera H.,

Maas D., Sutton S. and Zinner E. (1986) LPSC 17, 456-457. (3) Fechtig

H., Horz F., Igenbergs E., Jessberger E., Kuczera H., Lange G., Pailer

N., Sutton S., Swan P., Walker R. and Zinner E. (1985) In Properties

and Interactions oJ'/nterplanetary Dust (eds. R. H. Giese and P. Lamy),

pp. 121-126. Reidel.

Interstellar SiC and its origins. II. Ne -E without Na 23, and other surprises. Sachiko Amari, Roy S. Lewis and Edward Anders. Enrico

Fermi Institute and Dept. of Chemistry, Univ. of Chicago,

IL 60637-1433, USA.

Our new SiC size fractions (1) have very high noble-gas concentrati

(e.g.. He' to 0.1 1 ml/g, Ne„ 72 to 35 000 x 10 ­ 1 ml/g, Xe, 10 to 1100

10 1 ” ml/g), exceeding those of previous separates (2, 3) by -3-IO

As most previous samples were > 90% pure SiC, the reason is not hin

b

purity but presumably loss of gas-rich grains or surface layers i

earlier separations, either by chemical etching or by mechanical an

sion. He and Ne concentrations rise slightly with increasing grain

peaking at -I um, whereas Kr stays flat and Xe declines. Elemen

and isotopic ratios show regular trends, and usually lie between th

values calculated (4, 5) for the He-burning shells and envelopes of AGE

(asymptotic giant branch) carbon stars. The example in Table 1 refta.

to a 1.5 M. star of metallicity Z = 0.009 and C/O = 1 (4).

This match has important implications for the origin of Ne-E(14

The Ne in AGB star He-shells (4) actually is closer to pure Ne u that

the Ne in SiC (Table 1), and thus could serve as the sole source of N0.

E, without any help from Nall. Lacking non-volatile progenitors, He'

and KrI2 must have been trapped by ion implantation, and since He'/

NeE22 and Ne22/KrR2 ratios do not exceed those in the star, there ism

room for additional contributions by Na". At least Ne-E(H) may be i

"parentless, " nuc1eosynthetic Ne. I

The new samples still contain excess—presumably cosmogenic-Ne 3 l

relative to He-shell values (Table 1). Cosmic-ray exposure ages, al-'i

culated as before (2, 3, 6), range from 27 to 135 Ma, compared to the

previous mean of -40 Ma. The ages correlate with Ne 21 content and,

with severity of the chemical treatment, suggesting that the samples arc

mixtures of gas-rich, old, reactive (radiation-damaged?) grains, and gas•

poor, young, resistant grains (degassed during formation of the solar

system?). The true age of the old grains thus must be higher than the

age of the bulk samples, perhaps approaching the theoretical age of

-400 Ma. Acknowledgement: We thank R. Gallino and colleagues for

making available to us theirs-process calculations. References: (1) Lewis

R. S., Amari S. and Anders E. (1990) Meteoritics 25, 379. (2) AmariS.

and Lewis R. S. (1989) Neteorities 24, 247-248. (3) Zinner E., Tang K

and Anders E. (1989) GCA 53, 3273-3290. (4) Gallino R., BussoM,

Picchio G. and Raiteri C. M. (1990) Nature 348, 298-302. (5) Lewis K

S., Amari S. and Anders E. (1990) Nature 348, 293-298. (6) Tang M

and Anders E. (1988) Astrophys. J. 338, 1-31-1,34.

TABLE I

Sample S ize (um)

He 3.

He'

He'

Ne'-2

Ne 20

Ne

22

Ne216

Ne 22

Ne 22

Kr"'-

Kt',80

Yr^82

Kr,86

Kr,92

Xe130

Xe172

KJB 0.1-0.2 2.00 763 0.893 7.7 1560 0.050 0.65 0.360

KJC 0.2-0.3 1.48 618 0.636 9.1 2800 0.044 1.13 0.360

KID 0.3-0.5 1.16 478 0.459 10.7 4600 0.040 1.76 0.356

KIE 0.5-0.8 0.81 372 0.298 12.8 6700 0.036 2.42 0.346

He-shell (4) --0 384 0.073 5.4 13 800 0.036 2.28 0.41

Envelope (4) 9.6 10 600 5.76 142 18 000 0.056 1.77 0.25

a x 10-4.

" Extrapolated to Ne20/Ne22 = 0.04 along trends defined by the data; x I0-'

Two types of interstellar carbon grains in the Murchison carbonaceous

chondrite. S. Amari,'- 2 E. Zinner 2 and R. S. Lewis.' 'Enrico Fermi

Institute and Department of Chemistry, University of Chicago, Chicago, IL 60637, USA. 2 McDonnell Center for the Space Sciences and

the Physics Department, Washington University, St. Louis, MO 63130,

USA.

The carrier of Ne-E(L), Ca, consists of dense, round grains of carbon,

1-6 um in diameter (1, 2), ranging from well crystalized graphite to

"more organic" compositions and with 13013C ratios from 8 to 4500

(2). Noble gas data on density fractions indicate that there are at least

two types of Ca that differ in the release temperature of Ne-E(L) (3, 4).

In order to establish whether these two types also differ in their chemical and C-isotopic properties, we analyzed round grains from two density separates (4) in the ion microprobe: from KFA1 (density = 2.05-

2.10 g/cm', 22 Ne-E(L) = 13000 x 10- 9 cm2/g, two Ne-E release peaks

at 600 °C and 800-900 °C) and KFC 1 (density = 2.15-2.20 g/cm 2 , 22NeE(L) = 5150 x 10-" cm 3/g, only one release peak at 900 °C). Although

both separates contain grains with isotopically light and heavy carbon,

they have markedly different distributions (Fig. 1): while KFA 1 consists

mostly of isotopically heavy (a total of 16) and normal grains (12) with

fewer light grains (7), KFC1 consists predominantly of light grains (39),

with only few heavy (8) and normal (3) ones. The range of 12C/13C in

both separates is the same as that observed previously in Murchison

separate LFCI (2), except for one KFCI grain with 12C/ 13C = 4.12 (611C

_ +20 590 ± 160%.).

Zinner ei al. (2) noted that isotopically heavier grains have higher H,

N and Si contents than light ones. Thus, the first type, Cal, appears to

consist of heavy carbon of lower density with generally higher contents

of other elements, that outgasses at lower temperature (also evidenced
101

100

10-1

10'2

10.3

104

10.5

10 3

102

101

100

10 -1

10"2

100 200 300 400 500

Distance (μm)

100 200 300 400 500

--0-16 0

24Mg

p_ 27A1

—°— 28 S i

40 Ca

o _ 48 Ti

56 Fe

60Ni

181Ta

i

i

r y^

0

--o—Al/Mg

—0 — Si/Mg

—n—Ca/Mg

--a—Ti/Mg

YFc/Mg

Abstracts for the 54th Annual Meteoritical Society Meeting 1991

SIMS ANALYSIS OF MICROMETEOROID IMPACTS ON LDEF; S. Amaril,

J. Foote l , E. K. Jessberger2 , C. Simon l , F. Stadermann2 , P. Swanl , R. M. Walkerl and E.

Zinnerl , lMcDonnell Center for the Space Sciences and Physics Dept., Washington University,

One Brookings Drive, St. Louis, MO 63132, 2Max-Planck-Institut fur Kernphysik, Postfach

103980, D6900, Heidelberg, Germany.

LDEF experiment A0187-2 consisted of 237 capture cells, 120 on the leading edge, the

rest on the trailing edge. In each cell a 2 gm plastic foil, metallized on both sides, covered polished

Ge targets. Although all plastic covers except for 12 cells on the trailing edge failed during flight,

the Ge plates contain many extended impact features that were apparently produced by projectile

material that had penetrated the plastic foils while they were still intact. We optically scanned all

cells without plastic foil from the trailing edge and found extended impact features from 200 to

4000 gm in diameter with 4 characteristic morphologies: a. craters surrounded by deposits, b.

ring-shaped features, c. sprays, and d. "spider webs." 53 impacts were selected as high priority

candidates for ion probe analysis. After detailed documentation in the SEM impacts were analyzed

in the ion microprobe for the chemical composition of the remaining projectile material. Prior

simulation studies [1] had shown that extended impact on the Ge plates contained sufficient

projectile material for chemical and isotopic analysis by SIMS. We made multi-element point

analyses in lateral scans across the impact features. Each point analysis consisted of depth profiles

of a number of elements. In all of 12 impacts so far studied we found evidence for the presence of

projectile material in the form of elemental enhancements in the impact region, in 5 cases significant

amounts of projectile material were detected. One such analysis is shown in Figs. 1 and 2. Fig. 1

shows ion signals of different isotopes normalized to the 76Ge signal for a scan across a "spider

web" impact. In Fig. 2 the selected signals of 27 A1, 28Si, 40Ca, 48Ti and 56Fe were normalized

with relative sensitivity factors determined from laboratory studies [1] to obtain elemental

abundance ratios relative to Mg. Their abundances indicate an extraterrestrial origin except for Si,

which is anomalously high and is probably dominated by contamination from RTV glue used to

bond the Ge plates to the Al substrate. Enough material is present to allow isotopic measurements,

which will be reported at the meeting.

[1] Lange G. et al. (1986) Lunar Planet..Sci. XVII, 456.

Distance (μm)
Lunar Planetary Science XXIII, 1992

SIMS CHEMICAL ANALYSIS OF EXTENDED IMPACTS ON THE

LEADING AND TRAILING EDGES OF LDEF EXPERIMENT A0187-2. S.

Amari l , J. Foote r , C. Simon y , P. Swan s , R. M. Walkerl , E. Zinnerl , E. K. Jessberger2, G.

Lange2 , and F. Stadermann2. 1McDonnell Center for the Space Sciences and the Physics

Department, Washington University, One Brookings Drive, St. Louis, MO 63130-4899. 2MaxPlanck-Institut fur Kernphysik, Postfach 103980, D-6900 Heidelberg, Germany.

Experiment AO 187-2 on LDEF consisted of 237 capture cells each 8.6 x 9.4 cm in size.

Each cell consisted of four polished high purity Ge target plates, 42 x 39 x 0.5 mm, covered with

a 2.5 pm thick mylar cover foil spaced 200 gm from the Ge plates. The mylar was coated with

1000 of Ta on the side facing the Ge to facilitate ion-probe analysis, and was coated with 100

A of Au-Pd on-the top (space-facing) side to inhibit space erosion of the plastic. 120 cells were

mounted in a tray on the leading edge of the spacecraft and 117 cells were mounted in portions of

two separate trays on the trailing edge. Following the return of LDEF to earth after a much

longer mission than originally planned, it was found that most of the plastic cover foils had

failed. All of the foils on the leading edge were gone and only twelve cells on the trailing edge

were still intact.

However, optical microscope and SEM examination showed that many of the bare cells

on both the leading and trailing edges possessed numerous "extended impacts" that must have

been caused by the clouds of debris formed when incoming particles traversed foils that were

still intact at the time of impact. Our initial efforts have focussed on the ion probe study of

extended impacts on the trailing edge cells that had lost their plastic foils. As described in more

detail in a paper presented at the First LDEF Post-Retrieval Symposium [1], some 53 candidate

impacts were found by optical scanning of 116 cells on the trailing edge. Successful ion probe

analyses using our modified CAMECA IMS 3f instrument have now been performed on 40 of

these impacts. Lateral scanning profiles across these impacts were made by rastering an 0-

primary ion beam of 1-2 nA over an area 40 μm x 40 gm and then stepping across the impact.

Multi-element depth profiles were obtained at each analysis site by cycling through a series of

isotopic masses. Individual depth profiles were then integrated from cycles 3 to 20 to obtain an

integrated secondary ion, count for each point in a lateral traverse. Although the ion signals did

not match perfectly the appearance of the impacts as seen in the SEM, projectile debris material

could be detected in almost every impact (see Fig. 1). We found that the ratios of different

elements were somewhat variable across individual lateral traverses — either due to

inhomogenities in the projectiles themselves or to variable segregation of elements in the impact

and collection processes. Rather than attempting to integrate the data across a single lateral

traverse of a complex impact structure, we choose to report element ratios determined from the

peak values seen in a traverse. Ion counts are converted to elemental ratios using the sensitivity

factors previously determined on four glass standards [2].

Histograms of the ratios of Al, Fe, and Ti relative to Mg for 40 impacts are shown in Fig.

2. It can be seen that the distribution of values for the impact projectiles overlap those previously

determined for IDPs [3] as well as average chondritic ratios. However, the average ratios for the

LDEF impacts are systematically higher for the refractory elements Al, Ca, and Ti than those for

either chondrites or IDPs. Conversely, the Fe/Mg ratios are systematically lower. Comparison

of these data with earlier elemental fractionation trends obtained from studies of laboratory

impacts of standard glasses [2] led us to suggest [1] that many of the apparent differences could

be attributed to selective volatilization and redistribution of elements between the projectile as it

existed in space and the deposits that are measured. The new data are consistent with the earlier

results and can be similarly interpreted. However, it should be noted that the required elemental

fractionation exceeds that previously measured (or extrapolated) for laboratory impacts and a

difference between the interplanetary particles studied here and IDPs cannot be excluded. In

particular we note that Ca depletions which have been observed for IDPs [4] do not seem to be

reflected in the LDEF impacts.

Optical scanning of the bare leading edge cells also shows many extended impacts.

Although this demonstrates that the cover foils remained intact for some time after the deployment
24 Mg+ — ♦ 27Al+

40c+

—0-- 48Ti+

— t}— 52 Cr+

—Cl— S6Fe+

72Ge

500 1000 1500 2000

SIMS ANALYSIS OF LDEF: S. Amari ct al.

of LDEF, further analysis will be

required to assess the value of the

leading edge cells for the study of

cosmic dust and/or orbital debris.

A preliminary analysis of 7 front

bside impacts suggests that most of

them are due to space debris and

not micrometeoroids. A new

SIMS system for the analysis of

impact material based on ion

imaging of elements in the ion

probe is currently under

development.

References: [1] S. Amari et al.

(1991) Proc. 1st LDEF PostRetrieval Symp., in press. [2] G.

Lange et al. (1986) LPS XVII,

456. [3] F. Stadermann (1991)

unpublished data. [4] L. S.

Schramm et al. (1989) Meteoritics

24, 99.

AV,1tg ChoM. LDEF l

MP I

.001 .01 t.1 Lt it

/Mg LDEF

Chond.

MA

IDP

•i v

C

Fe/M& LDEF f

Cbond. I

EDP I

107

10°

105

1n

C 104

0

U

103 1

102

10'

41 .001 .01 0.1 1.0 .01 0.1 U 10 14

Fig. 2

E03-1-40B-1

Fig. 1

0

Distance (μm)
Germanium

Target 200

p

m

1

Cover Foil

NQ PAGE FOLA K NOT `FLNI, ^,

`^^^^^ ^'^ LPSC.XXV 1327

TRAJECTORY CALCULATION OF INDIVIDUAL PARTICLES FROM LDEF IMPACTS;

F. J. Stadermann, TH Darmstadt, Hilpertstr. 31(Geb. H); 64295 Darmstadt, Germany.

The capture cells from LDEF experiment A0187-2 were designed to determine the number and the chemical

composition of particles that impacted the surface of the satellite. During routine investigations elliptical

discolorations of the target material were observed adjacent to impact features. In a method demonstrated here, these

elliptical features are interpreted as results of erosion by atomic oxygen through holes in a cover foil. Based on this

assumption, it becomes possible to determine the pre-impact trajectories of individual particles in addition to their

original chemical composition. What makes this method particularly intriguing is the fact that it was unexpected and

that the experiment was not specially designed for this kind of investigation. It is the only experiment on LDEF that

offers this kind of combined trajectory and chemistry information of individual particles.

Impacting particle INTRODUCTION. The LDEF experiment

/Au-Pd coat (too A) A0187-2 consisted of germanium target plates and

—plastic foil (2,5 pm) a thin plastic foil, separated by 200 pm (Fig. 1).

^Ta coat (13oo A) Impacting particles were partly disrupted and

7mm F\\lq/^. elects decelerated while passing through the foil and

fragments of the particle were then collected both

— Getarget on the germanium plate and the back side of the

foil. The extended impact features found on the

Figure 1: Schematic of LDEF capture cell experiment A0187-2. germanium plates have typical diameters of

several hundred μm, although the sizes of the

corresponding projectiles (and of the holes in the foil) are only around 10 μm. Secondary ion mass spectrometry was

then used to determine the composition of impact deposits and to infer the origin (natural or man-made) of

individual particles [1]. Several extended impacts are accompanied by elliptical features (discolorations) of unknown

origin on the target plate [2]. These elliptical features have diameters of around 400 μm and are always directly

adjacent to or overlapping impact features. Although trays from experiment A0187-2 with identical setups were

located on various differently oriented LDEF surfaces, the elliptical features are only found on tray E08 on the

leading edge. On this leading edge tray none of the cover foils survived the extended exposure of the satellite, but at

the time of the impacts the foils must still have

Location d Leading Edge

Tray 'E06' been intact. Thee e elliptical features mayY be

s g explained as surface erosion effects by atomic

s b ^^ 100

144^^

oxygen through the impact holes in the foils at a

5 48-84V 11 atime when the latter were stillintact. Based on this

4 '0' 12 assumption it is possible to determine (a) the exact

Trailing Edge3 2 1 positions of the impact holes in the foils, (b) the

so° actual distances of the foils from the germanium

plates, and c J the trajectories of individual

Hole in Foil impact. from Pro upon m

ectile ;>'::<_>>`tz>>':>>•<!'`.:::>'<<<<>><s >: projectiles Po P

Ellipse Extended Impact Feature

Eigure 2: Schematic of an impact event on tray E08 through

the cover foil. The orientation of tray E08 relative to the

LDEF flight direction is shown in the insert.

GEOMETRIC CONSIDERATIONS. The

LDEF satellite was exposed to atomic oxygen,

which hit the surface with a collision energy of

4-5 eV almost directly from the forward (ram)

direction. Tray E08 was facing sideways from the

leading edge at an angle of 30° as shown in Figure

2. Oxygen atoms entering the capture cell through

an impact hole from ram drection spread inside in i

the shape of a circular cone (Fig. 3). The vertex of

this cone corresponds to the hole in the foil, which

is assumed to be significantly smaller than the

features on the target plate. The area where this

cone intersects with the surface, i.e., where the

oxygen atoms collide with the germanium has the
REFERENCES. [1] Amari S. et al. (1992) Proc.

]e 1st LDEF Post-Retrieval Symposium [2] Amari S. et al

(1993) Proc. 2nd LDEF Post-Retrieval Symposium

1328 LPSCXX '

TRAJECTORY CALCULATION OF INDIVIDUAL PARTICLES FROM LDEF IMPACTS: Stadermann F. J.

Vertex

Ellipse

(Conic

Circular 0

Figure 3: Schematic of cone-shaped distribution of

atomic oxygen inside the capture cell and geometric

interpretation of the elliptical feature as a conic section.

shape of an ellipse. The visible discolorations on the

target show the range of physical or chemical reactions

between atomic oxygen and germanium. Since all foils

on the leading edge failed eventually, the entire surface

(also outside of the ellipses) was subject to atomic

oxygen at the end of the flight. Therefore the ellipses can

only be understood as temporal features due to the longer

exposure.

Mathematically an ellipse in a plane can be

expressed as a conic section from a circular cone. With

one additional piece of information — either the direction

of the axis of the cone or the distance of the vertex from

the surface — the cone's geometric properties can

unambiguously be determined. After the location of the

vertex of the cone (i.e., the location of the penetration

hole in the foil) has been calculated, the original

trajectory of the particle before the impact can be

calculated. For this the approximate location of the

center of the impact feature has to be determined

arbitrarily. The assumption that the 'center of gravity' of

the visible extended impact feature lies on the

extrapolated line of original particle trajectory may be a

good first order approximation. From this information

the impact angles a and * (as shown in Fig. 4) can be

calculated.

CONCLUSIONS. The method demonstrated here appears to be a viable way to determine individual particle

trajectories from a record stored in the impact and oxygen erosion features on germanium targets from LDEF

experiment A0187-2. It is possible to calculate particle trajectories relative to LDEF and — since LDEF was

stabilized in its orbit — relative to the Earth. This information is not sufficient to determine individual projectile

origins in the solar system by simply tracing back individual trajectories, because no information on the timing of the

impacts is available. However, it is possible to distinguish between circular and elliptical orbits, and different

entrance angles into the atmosphere. All this information can then be correlated with the measurements of the

chemical compositions of the same particles and, thus, lead to a comprehensive understanding of individual particle

histories. In previous studies [1, 2] the distribution of different extended impact features could not be explained, nor

could the directions of the impacts be determined from

the observed features on the germanium. A detailed

analysis of the impacts with ellipses may lead to a

o better understanding of the extended impact features

:................ .......... .............................. and may make it possible to deduce the approximate

angle of impact solely from the shape of the impact

feature. Once this step is reached, the study of

<'> individual particle trajectories can be extended to all Xi

impacts on germanium — even on the trailing edge.

This would lead to themmost co ete m 1 database of

^:::v:i?+}1i•:}. x,}^ ' rx{v}:•: ?:? : .4i$'r'itiY{'I.::: P

article trajectories and chemistryon LDEF.

Figured Geometry of impact angles a and 0 from

projectile trajectory.
LETTERS TO NATURE

Interstellar oxide grains

from the Tieschitz

ordinary chondrite

L. R. Nittler, C. M. O'D Alexander, X. Gao,

R. M. Walker & E. K. Zinner

McDonnell Center for the Space Sciences and Department of Physics,

Washington University, One Brookings Drive, St. Louis, Missouri,

63130-4899, USA

MosT material in the Solar System has an isotopic composition

that represents an average of the different stars that contributed

material to the protostellar cloud. Primitive meteorites, on the

other hand, preserve grains that retain the isotopic signatures of

their individual stellar sources' and thus provide valuable insight

into stellar and galactic evolution, nucleosynthesis, and solar nebular processes. A large number of pre-solar silicon carbide, graphite

and diamond grains have now been isolated"', but only three interstellar oxide grains have hitherto been recovered3"', even though

oxygen-rich stars are believed to be the dominant source of dust

in the Galaxy8.9. We report here the isolation of 21 interstellar

oxide grains from the Tieschitz meteorite. The grains exhibit a

wide range of oxygen isotope compositions, indicating that they

originated in several distinct stellar sources having different masses

and initial compositions. There is also evidence for the presence

of the short-lived radionuclide 26A1 in nine of the grains at the time

they formed. Although the isotopic compositions of many of the

grains are consistent with both observations and theoretical models

of oxygen-rich red giant stars, a significant fraction have no

observed stellar counterpart.

Different isotopes are produced by a variety of nucleosynthetic

processes, and the isotopic ratios in interstellar grains can therefore provide insight into the types of stellar sites that produced

them. Here we determine the isotopic compositions of 21 interNATURE VOL 370 11 AUGUST 1994 443

PREMING PAGE BLANK NOT FaMED
LElTERS TO NATURE 

stellar oxide grains isolated from the Tieschitz meteorite, and 

compare these values to astronomical observations and theoretical models of stellar evolution. 

A sample of the Tieschitz (H/L 3.6) ordinary chondrite was 

physically and chemically processed to produce a residue'0311, 

T8, in which chemically-resistant oxide phases were concentrated 

by a factor of -2.5 x lo5. For ion microprobe analysis, a suspension of T8 was deposited on a gold foil1' along with grains of 

the Burma Spinel oxygen isotope standard. To automatically 

locate rare interstellar oxides, a Photometrics CCD (chargecoupled device) camera was coupled to the microchannel plate/ 

fluorescent screen of the modified Cameca IMS-3F ion 

microprobe4 at Washington University. Low-mass-resolution 

ion images (in 160- and "0-) of oxide grains were digitized, 

and the '60/'80 ratios (0~4%) of individual grains were determined by image processing. Grains that deviated in duplicate 

analyses by more than 30 from the solar '60/'s0 ratio were 

selected for high-mass-resolution analysis. The high mass-resolving power needed to separate I60H- ions from the 170- ions 

precludes measurement of '60/170 ratios by ion imaging in our 

instrument. 

Ion imaging of -6,000 grains yielded 53 candidates, the 160/ 

18 0 and '60/'70 ratios of which were subsequently measured at 

high mass resolution. Of these grains, 20 corundum (A1203) and 

1 spinel (MgA1204) have a large range of anomalous (non-solar) 

160/'80 and 160/170 ratios (Fig. 1 and Table 1). Nine of the 

grains also have large 26Mg excesses, corresponding to initial 

26A1/27~I ratios of between 1.2~ and 7.8 x much 

higher than the maximim value of 5 x lo-' observed in primitive 

Solar System material (Fig. 2 and Table 1). All grains are 0.5- 

2 pm in size. For purposes of discussion, the 24 interstellar oxide 

grains found to date were divided into three groups on the basis 

of their oxygen isotope compositions (Fig. 1 and Table 1). Note 

that the range of oxygen isotope ratios usually observed in meteorites and terrestrial samples falls within the solar symbol in 

Fig. 1. 

Group 1 grains have significant enrichments in 170 and modest 

depletions in "0, similar to the isotopic compositions measured 

in 0-rich red giantsl3,l4 (Table 1 and Fig. 1). These stars are 

thought to produce 65-75% of all dust, or -80-90% of 0-rich 

dust, in the Galaxy839. Because of this similarity, Group 1 grains 

probably formed in the atmospheres of red giants. The oxygen 

isotope compositions of such stars have been successfully reproduced by theoretical models in terms of the so-called first dredgeup, which occurs after exhaustion of H in the stellar core"-'8. 

In this process, material that has undergone partial core Hburning via the CNO-cycle is mixed into the envelope. These 

models predict that the first dredge-up significantly decreases 

the envelope's initial l60/I70 ratio, the actual values depending 

primarily on stellar mass'6-18 (see Fig. 1). But the first dredgeup has only a relatively small effect on the 160/180 ratio (20- 

50% increase), and larger differences in this ratio must be due 

to differences in the initial isotopic compositions of different 

starsI7 (Fig. 1). Such differences are the result of Galactic chemical evolution, reflecting age differences of the stars and/or the 

spread in chemical compositions observed in newly formed stars 

within a given Galactic epoch19. The range of the oxygen isotope 

compositions observed in the Group 1 grains indicates that they 

originated from several distinct stellar sources with different 

masses as well as different initial compositions. 

As red giant stars continue to evolve, they can undergo two 

additional dredge-up episodesI5. The second dredge-up occurs 

only in >5Mo stars at the beginning of the asymptotic giant 

branch (AGB) phase, when He is exhausted in the star's core. 

The third dredge-up, which is experienced by all stars in the 1- 

8M0 range, occurs during the thermally pulsing (TP) AGB 

phase when H and He burn alternately in thin shells on top of 

an inert core consisting now of C and 0. These mixing episodes 

are not expected to significantly change the oxygen isotope composition of the envelope, although some spectroscopic observa10 4 -. 0 Pre TP-AGB stars 

A 0-rich TP-AGB stars 

0 C-rid TP-AGB stars 

0 Tiesditz oxide grains 

Grains from Murchison, 0 Orgueil and Bbhunpur 

' Group 1 

Hot-bottom burning 

andlor 

FIG. 1 a, Comparison of the oxygen isotope compositions of 24 interstellar oxide grains reported here and e~sewhere~-~ with those of red giant stars13.14.20.21 . The red giant stars in a have been divided into 

three groups based on their spectral types and models of their 

evolution15. The oxide grains have also been divided into three groups 

based on their oxygen isotope compositions. b, Diagram of the expected 

oxgyen isotope compositions of red giant envelopes after the first and 

second dredge-ups as a function of stellar mass and initial composition. 

After core- H-burning ceases, 170-enriched H-burnt material from the 

interior is mixed into the 0-rich envelope of a red giant during two 

dredge-up episodes15 (the second only in >5M, stars). The curve shows 

the predicted post-dredge-up ratios of stars with initially solar compositions but different masses18. The initial 160/170 ratio influences the 

final ratio only in (1-1.5)M0 starsi7. The 160/180 ratio is only slightly 

affected by these two dredge-ups1'. The range of 160/170 and 160/180 

ratios amongst Group 1 grains suggests that they come from several 

stars with different masses and different initial compositions. The initial 

oxygen isotope compositions, reflecting Galactic evolution, probably 

varied roughy as indicated (F. Timmes, personal communication). Subsequently, during the thermally pulsing asymptotic giant branch (TPAGB) phase a third multiple dredge-up episode brings "c-rich He-burnt 

mateiial to the surfaci. As a yes&, (1-5)~, stars will eventually 

become carbon stars (C/O>l), but for (5-8)Ma stars, H-burning at the 

base of the envelope (hot-bottom burning) is predicted to destroy "C 

and '0, thereby preventing formation of a carbon star3'. Note that 

oxide grains may form even in carbon-star envelopes3'. 

tions of TP-AGB stars suggest that their atmospheres have 

higher '60/180 and l60/I70 ratios than pre-TP-AGB 

stars~3,14,20,2~ (Fig. la). 

The third dredge-up is expected to bring to the star's surface 26 Al that was produced by shell H-burning at much higher temperatures than those reached during core H-b~rnin~",'~. Models 

predict envelope 26Al/27Al ratios in the range from 5 x to 

lo-', depending on stellar mass, mass loss rate and evolutionary 

stage during the TP-AGB phase. Eight of the ten Group 1 grains 

measured for Al-Mg have inferred initial 26Al/27Al ratios in this 

range (Fig. 2). An alternative production mechanism for 26A1 is 

H-burning at the base of the convective envelope of TP-AGB 

NATURE . VOL 370 . 11 AUGUST 1994 
LETTERS TO NATURE

TABLE 1 Isotopic compositions of 24 meteoritic interstellar oxide grains

Grain 170/160 180/160 26Mg*/24Mg 27AI/24Mg 26AV27Al Group

Solar 3.83 x 10-4 2.01 x 10-3

T1 5.01(39) x 10-4 1.66 (12) x 10-3 0.033 209(32) 51.6 x 10-4 1

T2 6.6 (1.1) x 10-4 1.44 (27) x 10-3 2.04 (19) 263(65) 7.8 (2.0) x 10-3 1

T7 5.05 (22) x 10-4 1.55(7) x 10-3 0.369 (15) 139(18) 2.65 (37) x 10-3 1

T9 2.63 (5) x 10-3 1.27 (5) x 10-3 0.586 (83) 1086 (98) 5.40 (90) x 10-4 1

T10 1.11(3) x 10-3 1.36(6) x 10-3 5 0.042 402(37) S 1.0 x 10-4 1

T11 1.14 (5) x 10-3 1.60 (10) x 10 -3 NA NA NA 1

T14 1.47 (5) x 10-3 1.57 (9) x 10-3 0.163 (81) 1351(271) 1.20 (64) x 10-4 1

T18 1.19 (8) x 10-3 1.35 (15) x 10 -3 NA NA NA 1

T19 7.50 (74) x 10-4 1.63 (19) x 10-3 NA NA NA 1

T20 5.38 (16) x 10-4 1.66 (47) x 10-3 0.0303 (14) 41(2) 7.34 (46) x 10-4 1

M83-5 7.92 (23) x 10-4 1.52 (5) x 10-3 1.96 (11) 2250 (109) 8.73 (64) x 10-4 1

Org-B 9.72 (10) x 10-4 1.99 (4) x 10-3 1.61(3) 1840 (90) 8.7 (1) x 10-4 1

B39 2.60 (6) x 10-3 1.17 (4) x 10-3 0.2336 (104) 136(14) 1.7 (0.2) x 10-3 1

T16 1.01(6) x 10-3 6.21(54) x 10-4 NA NA NA 1/2

T17 9.12 (76) x 10-4 4.30 (89) x 10-4 NA NA NA 1/2

T4 1.26 (11) x 10-3 1.47 (85) x 10-4 0.064 (13) 17.0 (2.3) 3.77 (91) x 10-3 2

T6 1.14(8) x 10-3 4.3 (2.6) x 10-5 0.423 (57) 106(16) 4.01(82) x 10-3 2

T12 1.36 (4) x 10-3 1.50(11) x 10-4 0.969 (81) 135(11) 7.19 (83) x 10-3 2

T13 6.72 (24) x 10-4 1.41(10) x 10-4 10.4 (13) 5442 (707) 1.90 (35) x 10-3 2

T3 2.92 (29) x 10-4 1.98 (13) x 10-3 _<0.0048 8.2(l) 56.0 x 10-4 3

T5 3.15 (11) x 10-4 1.02 (3) x 10-3 0.0099 47(6) -<2.1 x 10-4 3

T8 1.92 (51) x 10-4 1.85 (29) x 10 -3 NA NA NA 3

T15 3.20 (23) x 10-4 1.26 (6) x 10-3 NA NA NA 3

T21 3.25 (17) x 10-4 1.29 (59) x 10-3 0.025 549(33) _<4.6 x 10-5 3

The (meteorite) source of the grains is shown in the first column; Tieschitz (T), Murchison (M) 4, Orgueil (Org)3,5,6 and Bishunpur (B)7 . The grains

have been divided into three groups on the basis of their oxygen isotopic compositions. 26Mg* is the excess of 26 Mg after correction for mass

fractionation, and 26AV27AI is the initial ratio if all 26 Mg* results from the in situ decay of 26 Al. All errors, in parenthesis, are 16 and upper limits

are 26. All grains were analysed by SEM-EDS (Scanning electron microscopy-energy dispersive spectroscopy) after oxygen isotope measurements

but before Mg-AI analysis in the ion probe. All but grain T3 appear to be corundum (Al203). The AI/Mg ratio of grain T3, measured by EDS, is about

twice that expected for pure spinel (MgAl204) but much lower than those of the other grains. The ratio obtained in the subsequent ion-probe

analysis of T3 is even higher, suggesting that the grain may be an intergrowth of spine[ and corundum. The oxygen isotope ratios are given with

160 in the denominator because in the reverse case the errors are asymmetric and nonlinear.

stars of >5Mo (hot-bottom burning) 24,21 But during hotbottom burning the whole envelope is cycled through the hightemperature H-burning zone, resulting in the destruction of

essentially all 180 (producing high 160/180 ratios), in disagreement with the oxygen isotope ratios observed in Group 1 grains.

The oxygen isotope and 26Al/27A1 ratios of these grains thus

indicate that at least eight of them come from TP-AGB stars,

and at least two from red giants before they reached the TPAGB phase. It is worth noting that whereas the oxygen isotopes

in red giant envelopes can be measured astronomically-albeit

Oxide Grains

• Group 1 (Tieschitz) }P+ T13

O Group 1 (Orgueil,

Murchison & Bishunpur)

A Group 2 ,e

n Group 3 r M83-5

T12

J^

,yP

T6

yT9

T 5

T7 040

OR39

T1

T4 TAU

TI

T21

3s TI

26AU^^AI=O

10 100 1,000 10,000 27AV24Mg

FIG. 2 Plot of the 26Mg/24 Mg ratio versus the 27AI/24Mg ratio in 17 presolar oxide grains. The large 26 Mg excesses, compared to solar Mg

isotopic ratios, are best explained as the result of in situ decay of 26AI.

Also shown are AI-Mg evolution lines for five initial 26AV27Al ratios. The

27AI/24Mg ratios in most of the Tieschitz corundum grains are not as

high as might be expected, possibly because of significant background

contributions from isotopically normal Mg to the Mg analysis. However,

these contributions do not affect the inferred 26AI/27Al ratios.

with larger errors than those obtained in the grains-the determination of 26A1/27 Al ratios in such stars is only possible from

the laboratory analysis of pre-solar grains.

Unlike grains in Group 1, neither Group 2 nor Group 3 grains

have spectroscopic counterparts and we must rely solely on comparisons with stellar evolution models to infer their likely

sources. Group 2 grains have 170 and 26 A] enrichments, and 180

depletions that are much larger than previously observed in any

meteoritic material or star. Two other grains, which lie on the

edge of the carbon-star field, have intermediate 18 0 depletions.

Relatively low-temperature hot-bottom burning could destroy

essentially all 180 in an AGB envelope without significantly

changing the 16 Al and "0 abundances already established by

the first, second and third dredge-ups". Also, such isotopic compositions are predicted to exist at the surface of massive masslosing stars which have shed their envelopes, exposing the Hburnt interior (Wolf-Rayet stars during the Of-WN phases)26.

In any case, better modelling and more elemental and isotopic

data on Group 2 grains are necessary for distinguishing between

the two possible sources.

The Group 3 grains are moderately depleted in "0 relative

to the Solar System. They could conceivably have formed

around low-mass red giant stars that have experienced the first

dredge-up, provided that the initial 160/"0 ratios of the stars

were higher than the measured grain values and, therefore, the

solar value. On the other hand, massive stars (>10 M O ), which

contribute -6-12% of all Galactic dust"', produce large excesses

of 160 and 180 in certain shells21 that could come to the surface as

the star loses mass or could be ejected in a supernova explosion.

160 enrichments and depletions with respect to the terrestrial

isotopic ratios are common in materials of Solar System origin 28;

in meteorites the enrichments can reach up to 7% in corundum

(Al203 ) and spinel (MgAl204) from Ca-Al-rich inclusions29.

These enrichments prompted suggestions that 160-rich grains,

probably corundum and spinel, from a supernova were incompletely mixed into the Solar System28 . We have not found any

10.0

bA

1.0

N

0.1

NATURE • VOL 370 - 11 AUGUST 1994 445
LmER8 TO NATURE 

pre-solar grains with large 160 enrichments. The Group 3 grains 

are 160-rich, but not with respect to both 170 and 180. The 

discovery that 160 can undergo mass-independent gas-phase 

chemical fractionation from both 170 and ''0 has provided an 

alternative explanation for the observed 160 enrichments in Solar 

System material3'. 

Finally, if the Si/Al ratio is assumed to be solar in all stars 

and if all Al goes into corundum (Al,O,), interstellar corundum 

appears to be underabundant in meteorites, relative to interstellar Sic, by about a factor of between 20 and 50 (refs 4, 6, 10) 

when compaerd to estimated Galactic dust production rates8". 

This is in spite of the fact that, in the solar nebula, corundum 

should have been more stable than Sic. Possible explanations 

are that interstellar corundum has a finer grain size distribution 

than Sic and was thus not detected by our technique, that A1 

primarily condenses in other phases (such as silicates) that are 

less resistant to the chemical treatments used to isolate the grains 

or, most speculatively, that corundum has a shorter lifetime in 

the interstellar medium than Sic. 

Received 25 Februaly; accepted 28 June 1994. 

1. Anders, E. & Zinner, E. K. Meteoritics 28, 49&514 (1993). 

2. Ott, U. Nature 364, 25-33 (1993). 

3. Huss, G. R., Hutcheon. I. D.. Wasserburg. G. J. & Stone, J. Lunar planet. Sci. XXIII, 563- 

564 (1992). 

4. Nittler. L. R., Walker, R. M.. Zinner, E. K.. Hoppe, P. & Lewis. R. S. Lunarplanet. Scl. XXIV, 

1087-1088 (1993). 

5. Huss, G. R., Hutcheon, I. D., Fahev, A. J. & Wasserburg. G. J. Meteoritlcs 28. 369-370 

(1993). 

6. Hutcheon, I. D., Huss, G. R., Fahey, A. J. & Wasserburg, G. J. Astrophys. I. 425, L97-L100 

(1994). 

7. HUSS, G. R., Fahey, A. J.. Galiino, R. & Wasserburg, G. J. Astrophys. J. (in the press). 

8. Gehrz, R. D. in interstellar Dust (eds Ailamandola. L. J. & Tielens, A. G. G. ) 445-453 (Kluwer 

Academic, Dordrecht, 1989). 

9. Whittet. D. C. B. Dust in the Galactic Environment, 295 (Institute of Physics, Brlstol, 1992). 

10. Nittler, L. R., Alexander, C. M. O'D., Gao, X., Waiker. R. M & Zinner, E. K. Lunar planet. Sci. 

XXV, 10051006 (1994). 

11. Gao, X., Alexander, C. M. O'D., Swan, P. D. & Waiker, R. M. Lunar planet. Sci. XXV, 401- 

402 (1994). 

12. Zinner, E. K., Tang, M. & Anders, E. Geochim. cosmochim. Acta 53, 3273-3290 (1989). 

13. Harris, M. J. & Lambert. D. L. Astrophys. J. 285, 674-682 (1984). 

14. Smith, V. V. & Lambert, D. L. Astrophys. I. Suppl. Ser. 72, 387416 (1990). 

15. Iben. I. Jr. Astrophys. I. Suppi. Ser. 76, 55-114 (1991). 

16. Dearborn, D. S. P. Phys. Rep. 210,367-382 (1992). 

17. Boothroyd, A. I., Sackmann, I. J. & Wasserburg. G. J. Astrophys. I. (in the press). 

18. El Eid, M. F. Astr. Astrophys. 285, 915928 (1994). 

19. Edvardsson, B. et al. Astr. Astrophys. 275, 101-152 (1993). 

20. Harris, M. J., Lambert, D. L., Hinkle, K. H.. Gustafsson, B. & Eriksson. K. Astrophys. I. 316, 

294-304 (1987). 

21. Kahane, C., Cernicharo, J., Gomez-Gonzalez, J. & Guelin, M. Astr. Astrophys. 258, 235- 

250 (1992). 

22. Forestini, M., Pauius, G. & Arnould, M. Astr. Astrophys. 252, 597-604 (1991). 

23. Galiino, R., Raiteri. C. M., Busso, M. & Matteucci. F. Astrophys. I. (in the press). 

24. Nvrgaard, H. Astrophys. J. 236,895-898 (1980). 

25. Cameron, A. G. W. in Protostars and Planets ill (eds Levy, E. H. & Lunine. J. 1.) 47-73 (Univ. 

Arizona Press, 1993). 

26. Prantzos, N., Doom, C., Arnould, M. & de Loore, C. Astrophys. I. 304, 695-712 (1986). 

27. WOOSley, S. E. in Nucleosynthesis and Chemical Evolution (eds Hauck. B., Maeder, A. & 

Meynet. G.) 1-195 (Observatoire de Geneve. Geneva, 1986). 

28. Clayton, R. N., Grossman, L. & Mayeda, T. K. Science 182, 485-488 (1973). 

29. Vlrag, A., Zinner, E. K., Amari, S. & Anders, E. Geochim. Cosmochim. Acta 55, 2045-2062 

(1991). 

30. Thiemens, M. H. & Heidenreich, J. E. Science 219, 1073-1075 (1983). 

31. Renzini, A. & Voli. M. Astr. Astrophys. 94, 175-193 (1981). 

32. Lanimer, J. M., Schramm, D. N. & Grossman, L. Astrophys. I. 219,230-249 (1978) 

ACKNOWLEDGEMENTS. We thank G. Huss and A. G. W. Cameron for their constructive reviews. 

This work was supported by NASA. 

NATURE . VOL 370 . 11 AUGUST 1994 
LPSC XXVI (1995)

CONTINUED STUDIES OF INTERSTELLAR SIC GRAINS OF TYPE X; L. Nittler, S.

Amari, K. Kehm, R. Walker, and E. Zinner, McDonnell Center for the Space Sciences and Dept.

of Physics, Washington University, St. Louis, MO 63130-4899, USA. R. Lewis, Enrico Fermi

Institute, University of Chicago, 5630 Ellis Ave., Chicago, IL 60637-1433, USA.

Previous studies have demonstrated the usefulness of quantitative isotopic imaging in the

ion microprobe for efficiently locating rare presolar dust grains in meteorites [1-5]. To better

characterize rare subsets of interstellar SiC grains, we have continued ion imaging searches in

separates of the Murchison carbonaceous chondrite. Silicon isotopic mapping of 2750 SiC grains

from Murchison separate KJG (average size 3μm) revealed 22 new members of the rare (,,-, 1%)

sub-class of SiC, known as grains X [6]. We analyzed these by SIMS for their Si, C, and N

isotopic compositions, and fourteen grains by laser gas extraction for their He, Ne, Ar, Kr and Xe

compositions. None carry noble gases above detection limits. The 75-odd Murchison X grains

found to date [2,5-6] have C, N, Si, Al, Ca, and Ti isotopic ratios qualitatively consistent with a

type II supernova origin, although mixing of different nuclear burning zones must have occurred

and several puzzles remain. There appear to be at least four distinct sub-groups of the X grains,

based on their silicon isotopic compositions.

Of 2750 imaged KJG SiC grains, twenty-two showed high 28 Si/3O Si ratios, characteristic of

X grains. High-mass-resolution analyses of C, N, and Si isotopic ratios in the grains confirmed

excesses of 15N and 28Si and a wide range of C-isotopic ratios (Figures), as previously observed in

X grains [2,6]. Subsequent laser gas extraction analysis of fourteen of the grains found none with

detectable noble gases. Previous noble gas studies of individual interstellar SiC grains have shown

that only a small fraction (-5%) are gas-rich [7]. The lack of gas-rich grains in the current sample

may be due to the small number of grains or to extensive sputtering in the ion probe prior to noble

gas measurements. On the other hand, X grains may be fundamentally different with respect to

noble gases, as they are with respect to their other elements. Additional noble gas measurements

on a larger sample of X grains are planned.

The silicon isotopic compositions of 34 KJG and two KJH X grains [2,6] are shown in Figure

1. All of the grains are highly enriched in 28Si, relative to the solar system. Most of the grains lie

above a mixing line of slope 1 between pure 28 Si and solar system Si, and have been labeled X-A

[5]. The best-fit line to these grains has a slope of 0.69 ±.03 and passes through the origin, although

there is considerable scatter about this line. A few grains lie on or near the slope 1 line and represent

the sub-population X-B [5]. One KJG grain (245-4) lies well below the others and represents a

new sub-type, X-D (X-C also has only one member, which lies above the other data [5]). All of

the KJG and KJH X grains have isotopically heavy N: 14NI 15 N = 13-181 (Solar ratio=272) (Figure

2), and typically have higher N'contents than "mainstream" SiC. Carbon in these X grains, on the

other hand, ranges from very heavy to very light (18 < 12C/13C < 2500), relative to the solar ratio

of 89 (Figure 2). Previous measurements have revealed extremely high 26AV27AI ratios (0.1 - 0.6)

in all of the nine X grains where Al-Mg measurements were possible, as well as enrichments in

49Ti in four grains and 44Ca in one grain [2,6].

Type II supernovae (SN) have been proposed as the most likely stellar sources for X grains [6],

and they can explain, in principle, most of the isotopic signatures found in these grains, provided

different zones within the pre-supernova star are selectively mixed during the explosion. Zinner

et al. [8] have explored mixing in supernova models of different masses, and have successfully

reproduced the isotopic compositions of a class of interstellar graphite.grains. Although their results

provide strong evidence for extensive mixing in supernova ejecta, there are some serious problems

to quantitatively account for the isotopic compositions of SiC X grains by the same scheme. The

low 14NI15N ratios and high 12C/13C ratios seen in most X grains point to a contribution from

the He-burning region of the pre-SN star, whereas high 26AU27A1 ratios and low 12C/13C ratios

indicate a significant contribution from the overlaying zone, where H-burning by the CNO cycle

Of ,.., 

tJ -KATY
INTERSTELLAR SIC GRAINS X: L. Nittler et al.

has occurred. But this zone has much more nitrogen than the partially He-burnt zone, and this N is

essentially pure 14N, making it difficult to reconcile 26A1 and 13C excesses with the 15 N excesses

characteristic of all X grains, and to explain the high N contents of the grains. The silicon isotopic

compositions of X grains can be explained qualitatively by invoking mixing of material from the

inner 0- and Ne-burning zones of the star, which produce essentially pure 28 Si, with the outer

H- and He-burning regions. Ca and Ti anomalies in X grains also point to a contribution from

these inner zones [6,9]. However, problems arise when attempting to quantitatively reproduce the

observed silicon isotopic ratios. In particular, the enrichment of 29Si relative to 30Si in grains X-A

is not predicted in regions with appreciable amounts of 28 Si [10].

Ion imaging provides an efficient method for identifying relatively large numbers of the rare

class of interstellar dust, SiC grains X. Together with low density graphite grains [8-9], and

perhaps the recently discovered nitrides [I 1- 12], these interesting grains are sensitive probes of the

complicated physics of exploding stars. Further isotopic measurements on these grains, particularly

of trace elements such as noble gases, Ca and Ti, will likely provide ever more stringent constraints

on models of supernovae and on the number of such stars which contributed material to the solar

nebula.

REFERENCES [1] Nittler, L. R.

et al. (1993) LPS 24, 1087. [2] Nittler, L. et al. (1993) Meteoritics 28,

413. [3] Nittler, L. R. et al. (1994)

Nature 370, 443. [4] Hoppe, P. et

al.(1994) Meteoritics 29, 474. [5] a

Hoppe, P. et al. (1995) This volume.

[6] Amari, S. et al.(1992) Ap. J.

394, L43. [7] Nichols, R. H., Jr. et

al.(1993) Meteoritics 28, 410. [8]

Zinner, E. et al.(1995) This volume. [9] Amari, S. et al.(1995)

This volume. [10] Woosley, S. E.

and Weaver, T. A. (1995) Ap. J.

submitted. [11] Alexander, C. M.

O'D. (1993) GCA 57, 2869. [12]

Hoppe, P. etal.(1994) LPS 25, 563.

° KJG & KJH X Grains

• X-A * •

q X-B

-200 X-D g 0

•

•

$oQ

400-e • • q

Q7AS-4 Figure 1

-600

-800 -600 -400 -200 C

S3'si (%o)

KJG & KJH X Grains

• X-A

q X-B

0

• ti

Figure 2 0 •

100 1000 10000

1000

Z

Z 100

2

10

10 12c/13C
intent to preserve the samples themselves under clean room conditions for the indefinite future and

to make sure that adequate documentation is maintained so that access to the samples is not

compromised by future changes in laboratory personnel. It will likely be a long time before an

experiment as large and specialized as AO187-2 will be flown in space for an extended duration —

LDEF is unique in this respect.

REFERENCES

1. Amari S., Foote J., Simon C., Swan P., Walker R.M., Zinner E., Jessberger E.K., Lange

G., and Stadermann F. (1991) SIMS chemical analysis of extended impact features from the

trailing edge portion of experiment AO 187-2. In LDEF — 69 Months in Space. First PostRetrieval Symposium (A.S. Levine, ed.), NASA CP-3134 (Part 1), 503-516.

2. Amari S., Foote J., Swan P., Walker R.M., Zinner E., and Lange G. (1993) SIMS chemical

analysis of extended impacts on the leading and trailing edges of LDEF experiment AO 187-2.

In LDEF — 69 Months in Space. Second Post-Retrieval Symposium (A.S. Levine, ed.),

NASA CP-3194 (Part 2), 513-528.

3. Stadermann F. J., Amari S., Foote J., Swan P., Walker R.M., and Zinner E. (1995) SIMS

chemical and isotopic analysis of impact features from LDEF experiments AO187-1 and

AO187-2. In LDEF-69 Months in Space. Third Post-Retrieval Symposium (A.S. Levine,

ed.), NASA CP-3275, 461-473.

4. Amari S., Foote J., Simon C., Swan P., Walker R., Zinner E., and Jessberger E. K. (1990)

Micrometeoroid experiment on the long duration exposure facility. Meteoritics 25, 347-348.

5. Amari S., Foote J., Jessberger E. K., Simon C., Stadermann F., Swan P., Walker R.M.,

and Zinner E. (1991) SIMS analysis of micrometeoroid impacts on LDEF. Meteoritics 26,

313.

6. Amari S., Foote J., Simon C., Swan P., Walker R. M., Zinner E., Jessberger E. K., Lange

G., and Stadermann F. (1992) SIMS chemical analysis of extended impacts on the leading

and trailing edges of LDEF experiment AO187-2. LPSC XXIII, 25-26.

7. Stadermann F. J. (1994) Trajectory calculation of individual particles from LDEF impacts.

LPSC XXV, 1327-1328.

8. Nittler L., Alexander C.M.O'D., Gao X., Walker R.M., and Zinner E. (1994) Interstellar

oxide grains from the Tieschitz ordinary chondrite. Nature 370, 443-446.

9. Nittler L., Amari S., Kehm K., Walker R., and Zinner E. (1995) Continued studies of

interstellar SiC grains of type X. LPSC XXVI, 1057-1058.

5