NASA-CR-194584

WORKSHOP ON

INNOVATIVE INSTRUMENTATION

FOR THE IN SITU STUDY OF

ATMOSPHERE^SURFACE

INTERACTIONS ON MARS

Mars Surface and Atmosphere Through Time

(NASA-CR-194584) MSATT WORKSHOP ON

INNOVATIVE INSTRUMENTATION FOR THE

IN SITU STUDY OF ATMOSPHERE-SURFACE

INTERACTIONS ON MARS (Lunar and

Planetary Inst.) 25 p

N94-22430

—THRU—

N94-22437

Unclas

G3/35 0191373

LPI Technical Report Number 92-07, Part 1

LUNAR AND PLANETARY INSTITUTE 3600 BAY AREA BOULEVARD HOUSTON TX 77058-1113

LP1/TR-92-07, Part 1
WORKSHOP ON

INNOVATIVE INSTRUMENTATION FOR THE IN SITU STUDY OF

ATMOSPHERE-SURFACE INTERACTIONS ON MARS

Edited by

Bruce Fegley Jr. and Heinrich Wanke

Held at

Mainz, Germany

October 8-9, 1992

Lunar and Planetary Institute 3600 Bay Area Boulevard Houston TX 77058-1113

LPI Technical Report Number 92-07, Part 1

LPI/TR--92-07, Part 1
Compiled in 1992 by

LUNAR AND PLANETARY INSTITUTE

The Institute is operated by the Universities Space Research Association under Contract No. NASW4574 with the National Aeronautics and Space Administration.

Material in this volume may be copied without restraint for library, abstract service, education, or personal research purposes; however, republication of any paper or portion thereof requires the written permission of the authors as well as the appropriate acknowledgment of this publication.

This report may be cited as

Fegley B. Jr. and Wanke H., eds. (1992) Workshop on Innovative Instrumentation for the In Situ Study

of Atmosphere-Surface Interactions on Mars. LPI Tech. Rpt. 92-07, Part 1, Lunar and Planetary Institute, Houston. 19 pp.

This report is distributed by

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PREFACE

This volume contains papers that have been accepted for the MSATT Workshop on Innovative Instrumentation for the In Situ Study of Atmosphere-Surface Interaction of Mars, October 8-9,1992, in

Mainz, Germany. The Scientific Organizing Committee consisted of B. Fegley Jr. (Washington University) and H. Wanke (Max-Planck-Institut fur Chemie), co-conveners, and L. M. Mukhin (Max-PlanckInstitut fiir Chemie).

Administrative support was provided by the Program Services Department staff at the Lunar and Planetary Institute. This volume was prepared by the Publications Services Department staff at the Lunar

and Planetary Institute.
CONTENTS

A Backscatter Mossbauer Spectrometer (BaMS)for Use on Mars

D. G. Agresti, R. V. Morris, E. L. Wills, T. D. Shelfer, M. M. Pimperl,

M.-H. Shen, andT. Nguyen 1

The Potential Utility of Spectral Reflectance and Emission Observations

to Martian Landers

R. E. Arvidson, M. K. Shepard, and B. Rivard 2

Database of Proposed Pay loads and Instruments for SEI Missions

N. G. Barlow 2

An Overview of Important Scientific Questions About Atmosphere-Surface

Interactions on Mars

B.FegleyJr 3

A Possible Use of Semiconductor Gas Sensor Instrument for Investigation of

UV'-Decomposition of Martian Salts and Release ofCl- and S-containing

Gases to the Atmosphere

M. V. Gerasimov 4

Determination of Martian Soil Mineralogy and Water Content Using

the Thermal Analyzer for Planetary Soils (TAPS)

J. L. Gooding, D. W. Ming, J. H. Allton, T. B. Byers, R. P. Dunn,

R L. Gibbons, D. B. Pate, and T. M. Polette 4

Ground-penetrating Radar As a Tool for Investigating Near-Surface Stratigraphy on Mars

J. A. Grant and P. H. Schultz 5

Analogue of Hand-Held Lens and Optical Microscope for Martian In Situ Studies

P. Jakes 7

Development of a Mossbauer Backscattering Spectrometer, Including X-Ray Fluorescence

Spectroscopy.for the In Situ Mineralogical Analysis of the Mars Surface

G. Klingelhofer, J. Fob, P. Held, H. Jager, R. Teucher, andE. Kankeleit 8

Magnetic Phases on the Martian Surface

J. M. Knudsen andL. Vistisen 9

Mass Spectrometric Studies of the Interaction of Martian Atmosphere Gas

Components with Ferric Oxide Surface Under UV Illumination

A. P. Koscheev and L. M. Mukhin 10

Does UV Instrumentation Effectively Measure Ozone Abundance?

B.L.Lindner 10

In Situ Identification of the Martian Surface Material and Its Interaction with

the Martian Atmosphere Using DTAIGC

R. L. Mancinelli and M. R. White 12
Atmospheric Imaging from Mars Landed Stations

T. Z. Martin 13

Mass Spectrometer-Pyrolysis Experiment for Atmospheric and Soil Sample Analysis

on the Surface of Mars

K. Mauersberger, P. Mahaffy, and H. Niemann 14

Temperature/Pressure and Water Vapor Sounding with Microwave Spectroscopy

D. O. Muhleman, M. A. Janssen, R. T. Clancy, M. Frerking, S. Gulkis,

D. J. McCleese, R. Zurek, andR. M. Haberle 14

Preliminary Experimental Results of UV Irradiation of Carbonates

L. M. Mukhin, J. Huth, H. Wanke, Y. Dikov, and A. P. Koscheev 15

COMPAS: Compositional Mineralogy Photoacoustic Spectrometer

W. H. Smith 16

Optical Luminescence Spectroscopy as a Probe of the Surface Mineralogy of Mars

A. H. Treiman 17

Mossbauer Spectroscopy on Mars: What to Expect

L. Vistisen and J. M. Knudsen 18

Determination of Stable Isotopic Compositions ofH, C, N, O, and S

at the Martian Surface Using Mass Spectrometry and

Stepped CombustionlPyrolysis

I. P. Wright, M. M. Grady, andC. T. Pillinger 19
LPl Technical Report 92-07, Part 1 1

N94-2243 1

A BACKSCATTER MOSSBAUER SPECTROMETER (BaMS)

FOR USE ON MARS. D. G. Agresti1-

3

. R. V. Morris2, E. L.

Wills», T. D. Shelferi, M. M. Pimperli, M.-H. Sheni, andT. Nguyen3,

'Physics Department, University of Alabama at Birmingham,

Birmingham AL 35294, USA,2Code SN4, Planetary Science Branch,

NASA Johnson Space Center, Houston TX 77058, USA,

 3Lockheed

Engineering and Sciences Co., Houston TX 77058. USA.

Introduction: We have proposed the use of Mossbauer spectroscopy for in situ analysis on the surface of Mars [1] and have

discussed the design and implementation of a backseatter Mossbauer

spectrometer (BaMS) instrument suitable for planetary missions to

the surfaces of Mars (MESUR), the Moon (Artemis and lunar

outpost), asteroids, or other solid solar system objects [2]. The BaMS

instrument is designed to be capable of analysis of a sample for the

mineralogy of its iron-bearing phases without any sample preparation.

A requirement of lander missions to Mars is instrumentation for

in situ mineralogical analyses. Such analyses provide data needed for

primary characterization as to the type of surface materials present

and by inference the processes that formed and subsequently modified them. For purposes of providing diagnostic information about

naturally occurring materials, the element iron is particularly important because it is abundant and multivalent (primarily 0, +2, and +3

oxidation states). Knowledge of the oxidation state of iron and its

distribution among iron-bearing mineralogies tightly constrains the

types of materials present The pivotal role of iron was already

recognized in 1978 by COMPLEX [3], who recommended development of flight instruments that would identify mineralogy and the

oxidation state of iron in planetary surface materials.

The near-term U.S. strategy for the exploration of Mars is the

MESUR (Mars Environmental SURvey) program, which entails

emplacement of a network of small, long-lived surface landers. For

the Moon, BaMS has been recommended as part of a three-instrument landed payload for the Artemis missions, targeted for 1997 [4].

BaMS would prospect for ilmenite, an oxygen resource material, and

provide data to assess the maturity of lunar soil. Because instrumental characteristics are low mass, low volume, and low power consumption, BaMS is suitable for implementation on even small

landers and rovers, as are being envisioned in MESUR and Artemis

concepts. In addition to providing highly diagnostic data, a BaMS

analyzer is inherently simple and, as is highly desirable for remote

operation, no sample preparation is required.

BaMS Instrument: Basically, a Mossbauer spectrometer consists of a multichannel analyzer, a 57Co source (for iron studies)

attached to a velocity transducer, and a radiation detector. Backscatter geometry, where the source and detector are on the same side of

the sample, will be employed so that no sample preparation is

required. For a planetary instrument, several modifications of the

transducer and detector components of a typical laboratory instrument are required to minimize mass, power, volume, and time

required for a good experiment.

Although we have tested solid-state translators as velocity transducers, the most likely to be implemented relatively quickly is a

miniaturized version of the conventional loudspeaker-type design.

Our current drive weighs ~20 g, operates at a vibration frequency of

-100 Hz, and requires -100 mW power [2]. It is rugged and suitable

for a planetary BaMS.

Conventional spectrometers generally employ gas-filled proportional counter detectors, and we have designed and tested one as a

backscatter detector [2]. However, silicon PIN diodes were introduced as part of a BaMS development for Mars '96 [5]. When

Side

View

X-rays

| Rock,_SoH,_etc._

Velocity

Transducer and

Gamma Ray

Source

Solid State and/or

Proportional Counter

Detectors

Fig. 1. BaMS schematic.

shielded from light, PIN detectors are suitable for detection of X-ray s

and gamma rays at energies required for Mossbauer spectroscopy

(6.4 and 14.4 keV). Advantages of PIN detectors over proportional

counters for planetary applications include small size (-0.2 cm3) and

low operating voltage (<100 V).

We are currently assembling and testing a BaMS instrument

(Fig. l)employing aminiature loudspeaker driveand an arrayof PIN

detectors to cover most of the 2n backscatter surface area. Based on

the mass and power consumption of brassboard components, we

project a BaMS instrument that will meet target specifications for a

flight unit of mass <500 g, volume <300 cm3, and power <2 W.

During BaMS instrument development, analytical performance is

evaluated with martian meteorite, martian analogue, and lunar

samples.

References: [1] Morris R. V. et al. (1989) LPSCXX. 721-722.

[2] Agresti D. G. (1992) Hyperfine Interactions. 72, 285-298.

[3] COMPLEX (Committee on Lunar and Planetary Exploration)

(1978) Strategy for Exploration of the Inner Planets: 1977-1987,

Space Science Board, National Academy of Sciences. [4] LPI(1992)

Workshop on Early Robotic Missions to the Moon, LPl, Houston.

[5] Klingelhofer G. et al. (1992) Hyperfine Interactions, 71,

1449-1452.
2 Workshop on Innovative Instrumentation

THE POTENTIAL UTILITY OF SPECTRAL REFLECTANCE AND EMISSION OBSERVATIONS TO MARTIAN

LANDERS. Raymond E. Arvidson1, Michael K. Shepard', and

Benoit Rivard2, 'McDonnell Center for the Space Sciences,

Department of Earth and Planetary Sciences, Washington University,

St. Louis MO 63130, USA,

 2Earth Observation Laboratory. Institute

for Space and Terrestrial Science, York University, North York,

Ontario, Canada M3J 3K1.

Estimates of surface thermal inertia derived from the Viking

Infrared Thermal Mapper demonstrate that bedrock outcrops are rare

[1]. Using IRTM data, Christensen [2] demonstrated that deviations

in blackbody behavior over diurnal cycles could be modeled as a

combination of high-thermal-inertiablocks and low-thermal-inertia,

fine-grained sediments. The two Viking Lander sites are located in

areas predicted to be among the blockiest on Mars. Viking Lander

images demonstrate that the two sites exhibit blocks of a variety of

sizes [3]. In addition, there is evidence for some bedrock outcrops at

the Mutch Memorial Station [3]. Six-channel (0.4-1.0 pm) Viking

Lander images show that most rocks have spectral reflectances

comparable to terrestrial basalts that are thinly coated with palagonite

or desert varnish [4]. Unfortunately, the six broadband channels

undersampled the spectral properties of rock and sediments, making

mineralogical identification tenuous at best.

The thesis of this abstract is to explore the additional mineralogical information that might have been obtained if the Viking Lander

imaging system had the capability to acquire high-spectral-resolution reflectance and emission data. Would it have been possible to

identify the mineralogy of bedrock, rock coatings, and sedimentary

deposits that are ubiquitous at both landing sites? The answers may

significantly affect measurement and planning strategies for future

lander missions to Mars. Acquisition of spectral reflectance and

emission data from a stationary or roving lander does not require

sample preparation and can be obtained anywhere within the field of

view of the imaging system. For roving landers, this ability would

greatly increase the reconnaissance potential of the lander since

compositionally interesting areas could be searched for before

committing the rover to a direction of travel. Thus, high-spectralresolution imaging data potentially offer a relatively inexpensive

way to acquire large amounts of mineralogical information.

In this work, we address the problem of identifying bedrock

mineralogy using high-spectral-resolution observations of blocks

modified by wind and coated with fine-grained aeolian sediment and

desert varnish. Samples of a number of natural rock surfaces,

collected at the Lunar Crater Volcanic Field, Nevada, and in the

Eastern Desert, Egypt [5], were used as analogues to blocks of the

martian surface. Samples consisted of rhyolites, andesites, and

basalts. Broken, fresh surfaces were also measured for control.

Samples were measured with high-spectral-resolution reflectance

(0.45-2.4 Jim, ~15-nm resolution) and thermal emission (7-14 (im,

~50-nm resolution) laboratory instrumentation. Lighting and viewing geometries were selected to simulate the Viking Lander observations.

For these samples, the extension of reflectance data beyond the

Lander's 1.0-fim limit provided information on the presence of

olivine and pyroxene due to electronic transition features (at -1 \im;

1 and 2 (im respectively) and hydrous phases via the 2.1- to 2.4-(lm

vibrational features [5]. Further, spectra of coated and fresh surfaces

tended to converge at longer wavelengths, suggesting a greater

degree of transparency of the coatings as wavelength increases. At

thermal emission wavelengths, the coatings were found to be less

important. Bedrock mineralogy, including fundamental vibrations

associated with Si-O bonds, dominated the spectra. These preliminary experiments demonstrate that high-spectral-resolution reflectance and emission observations provide direct mineralogical information even in the presence of coatings. Further, the information is

complementary in that absorption features due to charge transfers

and electronic transitions show up in the visible and near-infrared,

combination and overtone vibrational features also show up in the

near-infrared, and fundamental vibrations dominate the infrared.

In summary, if the Viking Landers had been equipped with highspectral-resolution reflectance and emission imaging capabilities,

the mineralogy of bedrock, blocks, and rock coatings would have

been discernible. Approaches for imaging instrumentation that acquire reflectance and emission data will be discussed at the workshop.

References: [1] KiefferH.H.etal.(1977)/Gfl.S2,4249-4291.

[2] Christensen P. R. (1986) Icarus. 68.217-238. [3] Arvidson R. E.

et al. (1989) Rev. Geophys., 27. 39-60. [4] Arvidson R. E. et al.

(1989) JGR. 94. 1537-1587. [5] Rivard B. (1992) Geology. 20.

295-298.

N94-2243 2

DATABASE OF PROPOSED PAYLOADS AND INSTRUMENTS FOR SEI MISSIONS. N. G. Barlow, Syscom

Development, Inc., Mail Code XI, NASA Johnson Space Center,

Houston TX 77058, USA.

A database of all payloads and instruments proposed for lunar and

Mars missions has been compiled by the author for the Exploration

Programs Office at NASA's Johnson Space Center. The database is

an outgrowth of the document produced by C. J. Budney et al. at the

Jet Propulsion Laboratory in 1991 [1]. The present database consists

not only of payloads proposed for human exploratory missions of the

Moon and Mars, but also experiments selected or proposed for

robotic precursor missions such as Lunar Scout, Mars Observer, and

MESUR. The database consists of two parts: a written payload

description and a matrix that provides a breakdown of payload

components. Each payload description consists of the following

information: (1) the rationale for why the instrument or payload

package is being proposed for operation on the Moon or Mars; (2) a

description of how the instrument works; (3) a breakdown of the

payload, providing detailed information about the mass, volume,

power requirements, and data rates for the constituent pieces of the

experiment; (4) estimates of the power consumption and data rate;

(5) how the data will be returned to Earth and distributed to the

scientific community; (6) any constraints on the location or conditions under which the instrument can or cannot operate; (7) what type

of crew interaction (if any) is needed; (8) how the payload is to be

delivered to the lunar or martian surface (along with alternative

delivery options); (9) how long the instrument or payload package

will take to set up; (10) what type of maintenance needs are

anticipated for the experiment; (11) stage of development for the

instrument and environmental conditions under which the instrument has been tested; (12) any interface required by the instrument

with the lander, a rover, an outpost, etc.; (13) information about how

often the experiment will need to be resupplied with parts or

consumables, if it is to be resupplied; (14) the name and affiliation

of a contact person for the experiment; and (15) references where

further information about the experiment can be found.

The payload matrix contains more specific information for each

experiment than does the payload description. The payload matrix is

an Excel chart containing information about the transport accommodations, deployed physical data, construction information, set-up
LPl Technical Report 92-07. Part 1 3

time and difficulty, surface accommodations, communication requirements, data formats, operation requirements, technology readiness level, and any unique requirements or comments for each

payload. The detailed breakdown of the information in the payload

matrix is as follows:

1. Transport Accommodations: mass, dimensions, volume,

power, thermal control, human interaction, and robotic interaction.

2. Deployed Physical Data: mass, volume, dimensions, and

location.

3. Construction: cleared surface area, excavation depth, and

excavated volume.

4. Set-Up: set-up IVA time, set-up EVA time, robotic set-up

time, assembly difficulty, and transport requirements.

5. Surface Accommodations: day power (operating and

standby), night power (operating and standby), waste heat generated,

heat rejection temperature, pressurized volume, and other services.

6. Communications: number of narrow data streams, number

of wide data streams, number of voice data streams, and number of

video channels.

7. Data: output data format, frequency, maximum data rate,

data volume, optimal storage method, optimal transmitlal method,

and in situ data processing requirements.

8. Operations: number of robotic hours/week, number of IVA

hours/week, number of EVA hours/week, training level, and crew

specialist requirements (type and time needed).

9. Technology Readiness: level.

10. Unique Requirements and Comments.

The payload description and matrix are designed to provide

scientists and engineers involved in the Space Exploration Initiative

programs with a continuously updated database of the various

experiments that have been proposed for robotic and human missions. The database contains information on all instruments proposed, not just those that have been officially selected for a particular

mission.

The database is continually evolving as new instrumentation is

proposed for the various missions to the Moon and Mars. Any

additions, comments, or suggestions about the database should be

directed to the author at the above address.

References: [1] Budney C. J. et al., eds. (1991) SEI Science

Pay loads: Descriptions and Delivery Requirements, JPL D—7955.

AN OVERVIEW OF IMPORT ANT SCIENTIFIC QUESTIONS

ABOUT ATMOSPHERE-SURFACE INTERACTIONS ON

MARS. Bruce Fegley Jr., Department of Earth and Planetary

Sciences and McDonnell Center for the Space Sciences, Washington

University, St. Louis MO 63130-4899, USA.

Introduction: The past three decades of Mars exploration and

observation have led to a dramatic increase in our knowledge of the

Red Planet, and have shown the seminal roles played by atmospheresurface interactions such as condensation and sublimation of CO2,

the dominant atmospheric constituent, and the condensation and

evaporation of water vapor, an important minor constituent. Other

types of atmosphere-surface interactions are also believed to be

important under martian surface conditions, but have not been firmly

identified. In this presentation I review some of the key issues about

atmospheric composition, lithospheric composition, and atmospheresurface interactions (e.g., chemical weathering) that remain unresolved, and mention possible measurements that may be used to

address these questions. This sets the stage for many of the presentations to be given at this workshop.

Atmospheric Composition: The key questions about martian

atmospheric composition include several related to the detection,

concentration, transport, and variations of various atmospheric

species that are either known to interact with the martian surface or

are thought to do so. Thus, questions such as the following need to

be addressed: (1) The spatial and temporal variation of water vapor

in the troposphere. Long-term, in situ data are needed to complement

and extend the results of Earth-based observations and the Viking

M AWD experiment. (2) The spatial and temporal variation of ozone,

a known product of martian atmospheric photochemistry. (3) The

behavior of CQ^, H2O, O3, and other predicted reactive trace gases

that are products of atmospheric photochemistry in the planetary

boundary layer. We observe that the martian surface is both a source

and a sink of CO2 and water vapor. It is reasonable to surmise that the

surface of Mars, like the surface of the Earth, is both an emitter and

a receiver of different atmospheric trace gases. Of course, this is for

different reasons than on the Earth, e.g., the presence of energetic

solar U V radiation and the lack of biological activity on Mars. To a

first approximation, qualitatively different behavior in the planetary

boundary lay er is expected over the polar caps and over the rest of the

rocky surface. (4) The detection and monitoring of as-yet unobserved, but predicted, products of atmospheric photochemistry.

These products include H2, H2O2, NO, NO^ and several highly

reactive radicals and atoms HO2, OH, O, and H [1—4]. Hydrogen

peroxide and other more complex peroxides that may form from it

have attracted great interest as possible explanations for the activity

observed by the Viking life detection experiments. Peroxides may

also be important oxidants in martian soils and "precipitation" [5].

Oxidation reactions of H2O2 with Fe-bearing minerals and other

transition-metal-bearing minerals are energetically very favorable

and may play a role in chemical weathering on Mars. (5) The

measurement and long-term monitoring at the martian surface of

CO, O2,03, and other products of photochemistry in the CO2-H2O

system is also potentially important for determining the importance

of heterogeneously catalyzed reactions in maintaining the stability of

the martian atmosphere against photochemical destruction. The

current gas-phase photochemical models need to invoke either

unreasonably high K^ coefficients or unreasonably high watervapor concentrations in order to account for the photochemical

stability of the atmosphere [1-4,6]. The importance of these heterogeneously catalyzed reactions is not well constrained at present, but

may be significant.

The isotopic composition of the different atmospheric gases is

also an important issue for several reasons: (1) The D/H ratio and

oxygen isotopic composition of water vapor, and the carbon and

oxygen isotopic composition of CO2 are important for assessing

models of volatile cycling between the atmosphere, regolith, and

polar caps. (2) High-accuracy and high-precision data comparable to

those from laboratory measurements of SNC meteorites are also

desirable for comparison with these putative martian samples. (3) A

knowledge of isotopic fractionations between different atmospheric

gases (e.g., oxygen isotopes in water vapor, CO2, CO, O2,03, etc.)

would help constrain models of atmospheric chemistry and would be

important for comparisons to terrestrial atmospheric chemistry.

Surface Composition and Chemical Weathering: Key questions about the composition of the surface of Mars include the

following: (1) Determination of the chemical, isotopic, and majorelement mineralogical composition of bulk rocky material at several

sites on the surface. This is important for comparison with the Viking

XRF data, for comparison with analyses of SNC meteorites, and for

constraints on cosmochemical modeling of the composition of Mars.

Important isotopic data include the

 17O/16O and 18O/16O ratios at an
4 Workshop on Innovative Inslrumcnlalion

accuracy and precision sufficient to resolve the expected small

difference from the terrestrial mixing line, and data for several

isotopic systems such as Nd-Sm, Rb-Sr, U-Pb, Pb-Pb, Hf-Lu, etc.,

used for geochronology. (2) Determination of the nature, abundance,

and geographical variations of Fe-bearing minerals on the martian

surface. Various Mossbauerspectroscopy instruments fordoing this

will be discussed at the workshop. (3) Determination of the nature

and abundance of minor and trace phases commonly expected to be

present on the martian surface. Such phases include carbonates,

nitrates, sulfates, and hydrated minerals [7]. Many of these phases

are expected to be products of chemical weathering reactions [8].

Several of the issues related to determining the nature and extent

of chemical weathering at the present and during the past include the

following: (4) Measurements of the chemical, isotopic, and mineralogical composition of weathering products found on different

rocks and minerals and similar measurements on the underlying

material. When coupled with measurements of the thickness of the

chemically weathered layer, the age of the layer (e.g., from cosmogenic nuclides), and the atmospheric composition, this would give a

knowledge of the gaseous and solid reactant compositions and of the

solid reaction product. Information about the timescale of the

weathering process would also be obtained. (5) Measurements of the

geographic variations (if any) in the nature and abundance of

weathering products. (6) Measurements of the relationship (if any)

between the nature and abundance of chemical weathering products

on minerals and rocks and solar U V illumination at the same site. The

importance of photochemical weathering on Mars is a controversial

topic that is being actively investigated by different laboratory

experiments. In situ measurements that can deconvolve present-day

and "fossil" weathering products will go a long way toward answering questions about the importance of photochemical weathering on

Mars.

Acknowledgments: This work was supported by grants from

the NASA Planetary Atmospheres and Mars Observer Participating

Scientist Programs.

References: [1] Parkinson T. D. and Hunten D. M. (1972) J.

Atmos. Sc».. 29.1380-1390. [2] McElroy M. B. and Donahue T. M.

(1972) Science, 177.986-988. [3] McElroy M. B. et al. (1977) ./G/?,

82, 4379-4388. [4] Yung Y. L. et al. (1977) Icarus, 30, 26-41.

[5] Hunten D. M. (1974) Rev. Geophys. Space Phys., 12,529-535.

[6] Atreya S. K. and Blamont J. E. (1990) GRL, 17, 287-290.

[7] Banin A. et al. (1992) In Mars (H. Kieffer et al., eds.), Univ. of

Arizona, in press. [8] Fegley B. Jr. andTreiman A. H. (\992)lnAGU

Geophysical Monograph No. 66 (J. G. Luhmann et al., eds.), 7—71.

A POSSIBLE USE OF SEMICONDUCTOR GAS SENSOR

INSTRUMENT FOR INVESTIGATION OF UVDECOMPOSITION OF MARTIAN SALTS AND RELEASE

OF Cl- AND S-CONTAINING GASES TO THE ATMOSPHERE. M. V. Gerasimov, Space Research Institute, Russian

Academy of Sciences, ul. Profsoyuznaya, 84/32, Moscow, Russia.

Martian soil contains a rather high concentration of salts composed mainly of sulfates and chlorides. Concentration of sulfates in

martian soil is estimated to be about 8-15% and concentration of

chlorides 0.5-1.5% [1]. The composition of martian salts is uncertain, but probably is a mixture of Mg, Ca, and Fe sulfates and

chlorides of Mg, Ca, Na, and Fe. The action of solar U V illumination

on the surface of the martian soil can result in the destruction of salts

and release of S- and Cl-containing gases (mainly SO2 and C12) to the

atmosphere. Trapping of these gases by atmospheric aerosols or dust

forms a certain step in cycles of S and Cl on Mars. Currently we do

not have much information about the mobility of S and Cl on Mars.

The concentration of SO2 and C12 in the martian atmosphere is

considered to be low (<0.1 ppm) [2,3] and cannot be measured by

orbiter spectroscopy methods down to the martian surface. For this

reason the in situ measurement of concentrations of S- and Clcontaining gases in the martian near-surface atmosphere can provide

important information about the role of UV radiation in S and Cl

cycles.

An experiment by Obvintseva et al. [4] measured the destruction

of AgCl salt under the action of U V radiation (1 ~ 300 nm). With

absorption of 1012-1013 photons s-1 the flow was SxlO11 to 5xl012

cnr2 s-1 of Cl atoms from the surface of AgCl salt. Decomposition of

AgCl salt proceeded with release of C12 molecules and Cl atoms. The

flow of Cl gases was measured using semiconductor gas sensors on

the basis of ZnO and NiO oxides. This experiment has two important

outcomes: (1) decomposition of salts under the action of UV luminosity can be a real and noticeable process for the martian environment and (2) semiconductor gas sensors can be valid for

measurement of gases that evolve during UV decomposition of salts.

A semiconductor gas sensor analyzer is now in preparation for the

Mars rover within the Russian Mars '94, '96 missions. It is a portable

instrument weighing less then 200 g. The main purpose of this

instrument is to measure minor components of the martian atmosphere such as H2O, CO, O2, and H2. The possible measurement of

S- and Cl-containing gases using a semiconductor gas sensor analyzer is discussed.

References: [1] Clark B. C. and van Hart D. C. (1981) Icarus,

45.370. [2] OwenT. andSaganC. (1972)/carus, 76,557. [3] Maguire

W.C.(1977)/carjtf,J2,85.[4]ObvintsevaL.A.etal.(1988)/./'Ayj.

Chem., 62,105 (in Russian).

N94-2243 3

DETERMINATION OFMARTIANSOILMINERALOGY AND

WATER CONTENT USING THE THERMAL ANALYZER

FOR PLANETARY SOILS (TAPS). James L. Gooding1,Douglas

W. Ming >, Judith H. Allton2, Terry B. Byers2, Robert P. Dunn2, Frank

L. Gibbons2, Daniel B. Pate2, and Thomas M. Polette2, 'Code SN,

NASA Johnson Space Center, Houston TX 77058 USA,

 2Lockheed

Engineering and Sciences Company, 2400 NASA Road 1, Houston

TX 77058, USA.

Physical and chemical interactions between the surface and

atmosphere of Mars can be expected to embody a strong cause-andeffect relationship with the minerals comprising the martian regolith. Many of the minerals in soils and sediments are probably

products of chemical weathering (involving surface/atmosphere or

surface/hydrosphere reactions) that could be expected to subsequently influence the sorption of atmospheric gases and water vapor.

Therefore, identification of the minerals in martian surface soils and

sediments is essential for understanding both past and present

interactions between the Mars surface and atmosphere. Clearly, the

most definitive mineral analyses would be achieved with wellpreserved samples returned to Earth-based laboratories [1]. In advance of a Mars sample return mission, however, significant progress

could be made with in situ experiments that fill current voids in

knowledge about the presence or abundance of key soil minerals such

as clays (layered-structured silicates), zeolites, and various salts,

including carbonates. TAPS is intended to answer that challenge by

providing first-order identification of soil and sediment minerals.

TAPS combines a differential scanning calorimeter (DSC) with

an evolved-gas analyzer (EGA) based on single-function gas sensors
LPl Technical Report 92-07, Part 1 5

THERMAL ANALYZER FOR PLANETARY SOILS (TAPS)

I Sample

I residue

;-— 4 planetary surface

• Acquire/accept sample

• Heat sample to expel gases

(upper temperature limit

is a design variable)

• Identify minerals or ices

(and their abundances)

by thermodynamic response

• Purge sample residue

(multi—sample versions only)

• Identify gaseous species

• Measure concentrations

• Water.

• Carbon, nitrogen,

and sulfur

compounds

DIGITALLY SIMULATED ANALYSIS OF

HYPOTHETICAL MARS SOIL SAMPLE

o

D.

</)

LLJ

or

a:

o

Gypsum.

CaSO

\ \

Goethite.

FeO(OH)

/\ / Aragonite

A ,/

. ". / "x

Aragonite,

calcite.

CoCO.

IbU/ '. / /••-.._ /

,-•"" Y~"~ Nontronite, ^""-. '

I NoOJFe2 (Si/,l)40,0(OH)2-nH20 \ j f

EGA

400 600 800 1000

SAMPLE TEMPERATURE (K)

QUANTITATIVE ANALYSIS:

• Deconvolution into components

• Library "fingerprint" identification

• Integration of individual peaks

• Application of calibration factors

Fig. 1. Functions and simulated data for a TAPS experiment appropriate for

small Mars landers. Correlation of DSC peaks with H2O or CO2 peaks from

EGA single-function gas sensors permits positive recognition of hydrate or

carbonate minerals respectively.

located in the DSC effluent gas stream (Fig. 1) [2]. DSC is the

quantitative measurement of the enthalpic response of a material to

a systematic change in temperature; the fundamental properties

measured are enthalpies and temperatures of phase transitions and

constant-pressure heat capacities [3]. DSC superficially resembles

differential thermal analysis (DTA), but is more quantitative and

versatile [3J. High-quality DSC analyses can be obtained on only a

few milligrams of solid materials.

A DSC/EGA combination applied to Mars can identify minerals

according to their heat-flow "fingerprints," using pattern-recognition strategies that are generally similar to those employed in

spectrophotometry [2,4]. The principal strength of DSC in the

planetary context is identification of ices and volatile-bearing minerals, including clays, hydrous salts and oxides, and carbonates.

Given the mineral identities, characteristic enthalpic peaks can be

integrated to yield relative proportions of the minerals present DSC

detection limits for hydrous minerals range from about 10 wt% for

clays to <1 wt% for iron oxyhydroxides and salts [5]. Unlike

spectrophotometry, DSC results are relatively insensitive to particle

coatings or other matrix effects. Although the appearance of a given

heat-flow curve can depend on the physical characteristics of the

sample, integrated ratios of enthalpic peaks change less severely

with physical properties than do peaks in reflectance spectra.

Although the EGA function is often equated with a gas chromatograph or mass spectrometer, smaller and simpler gas sensors offer

compact yet powerful alternatives. Forexample.capacitive-polymer

humidity sensors represent a recent technology [6] that our work has

shown can achieve precise EGA measurement of water with minimal

complexity [7]. Similar progress on microchemical sensors specific

to other gases is expected to provide additional opportunities for a

comprehensive EGA without the slow throughput of gas chromatographs or the vacuum requirements of mass spectrometers.

DSC-based experiments have been previously designed but never

flown on spacecraft. The Planetary Soil Water Analyzer (PSWA)

experiment [8], which included a DSC backed by an electrolytic-cell

detector for evolved water vapor, was developed in the early 1980s

as a post-Viking follow-on experiment for Mars. However, no

further Mars landing missions were flown and the PSWA project was

discontinued. A preliminary design for a DSC experiment, backed by

agas chromatograph as EGA, was included during the middle 1980s

in plans for the Comet Rendezvous and Asteroid Flyby (CRAF)

Penetrator-Lander, but the instrument was never built and CRAF was

cancelled.

In 1989, concepts for DSC-based planetary experiments were

renewed as the TAPS project with emphasis on applications to small

Mars landers. Work to date has addressed packaging concepts,

integrated sample-acquisition mechanisms, determination of sensitivity requirements, and evaluation of candidate water sensors.

Using 1980s technology, a version of TAPS packaged for Mars

applications is estimated to have the following attributes: 1.2 kg

mass, 850 cm3 volume, 5 W peak power, and 1.5 Whr per analysis.

Design, fabrication, and demonstration tests are in progress for a

prototype that will be complete in 1993.

References: [1] Gooding J. L. et al (1989) Eos, 70, 745,

754-755.[2]GoodmgJ.L.(1991)LPSC;CW/,457-458.[3]Wendlandt

W. W. (1986) Thermal Analysis, 3rd edition, Wiley, New York,

814 pp. [4] Gooding J. L.(1991)Proc.20thNorthAmericanThermal

Analysis Society Conf.. 329-334. [5] Gooding J. L. etal.(1991)jLPSC

XXII, 463-464. [6] Huang P. H. (1988) In Proceedings of Sensors

Expo, 106B1-106B16, Helmers, Peterborough, New Hampshire.

[7] Gooding J. L. et al. (1992) LPSC XXI11, 427-428. [8] Ball

Aerospace Systems Division (1982) Planetary Soil Water Analyzer

Final Report, 54 pp.

GROUND-PENETRATING RADAR AS A TOOL FOR

INVESTIGATING NEAR-SURFACE STRATIGRAPHY ON

MARS. J. A. Grant and P. H. Schultz, Department of Geological

Sciences, Brown University, Providence RI 02912, USA.

Despite the highly successful outcome of previous planetary

missions to Mars, fundamental questions remain regarding the

interaction between atmospheric and surface processes. For example, many characteristics of the near-surface stratigraphy (depths

less than -30-40 m) andsoils on the planet remain largely unknown.

Additionally, the nature and origin of fine-grained deposits mantling

portions of the cratered uplands and the near-surface of the northern
6 Workshop on Innovative Instrumentation

lowlands (e.g., [1—4]) preserve the long-term sedimentary history of

surface-atmosphere exchanges through time, but remain unexplored.

Ground-penetrating radar (GPR) is a proven and standard instrument

capable of imaging the subsurface to several tens of meters and could

help resolve these issues through definition of the geologic record

during future Mars missions. GPR data would also provide context

for interpreting results of other surface analyses (e.g., elemental or

mineralogical).

Previous terrestrial experience (e.g., [5,6]) with a GPR and

associated transducer frequencies between 50 and 500 MHz demonstrates the effectiveness of the instrument in definition of stratigraphy up to 30-40 m depth [5] and a resolution of up to 10-20 cm [6].

Moreover, successful GPR deployment in and around Meteor Crater,

Arizona, Odessa Craters, Texas, and the Rio Cuarto Craters, Argentina, highlights the capabilities of GPR in planetary settings [6]. Data

collected along short transects (10-100m) around these craters using

an analogue GPR produced easily recognized stratigraphic markers

corresponding to different ejecta compositions, alluvium, calcic

soils, and in situ bedrock (Figs. 1 and 2) all with dielectric constants

of 4-10. Excavation of groundtruth pits demonstrates that the GPR

reflectors are within 5-10 cm of the actual position of geologic

contacts. Prominent stratigraphic reflectors were identified even

where calcic soils were well developed (Fig. 2). Coupled with their

compact size, these characteristics imply GPR could define shallow

martian stratigraphy and should be considered as an instrument on

future rover missions.

Meteor Crater Medial Drainage Transect

GPR Data

(ns) (ns)

: .pproi.l g m

Interpretation

(cm)

1SO

Surface

Calcic

Alluvium

Kalbab Formation Ejecta

(cm)

150

Northwest •

Data collected using Geophysical Survey Systems. Inc.. SIR-3 and 500 MHz Transducer

Meteor Crater Distal Ejecta Lobe Transect

GPR Data

(ns)

15 L

(ns)

0 (scale ipprut.) 1 5 ,

Interpretation

(cm)

Surface •

\ V / \ \ Kaibab Formation EJecta / /

Moenkopl Formation Ejecta ?

"

In Situ Moenkopl Formation

(cm)

ISO

Data collected using Geophysical Survey Syslem. Inc. SIR-3 and 500 MHz Transducer

Fig. 1. AnalogueGPR transect across distal ejecta lobe superposing low buue

1.1 km north-northwest of Meteor Crater. Radar pulse travel time is in

nanoseconds and the depth is in centimeters. Ejecta derived from two excavated

lithologies is identifiable as is the underlying bedrock. Contacts were confirmed

by excavation.

Fig. 2. Analogue GPR transect through blocked drainage -0.5 km south of

Meteor Crater. Radar pulse travel time is in nanoseconds and the depth is in

centimeters. Ejecta and alluvium are clearly distinguished. The top of the calcic

soil horizon (6k horizon) is also identifiable. Discontinuous reflectors in the

ejecta are caused by buried blocks. Contacts were confirmed by excavation.

Definition of shallow stratigraphy on Mars using rover-mounted

GPR might resolve several issues regarding surface and atmospheric

evolution when accompanied by groundtruth from penetrators or

cores. First, the Viking landers revealed high sulphur contents in

surface duricrusts [7] whose origin may be related to either precipitation during ground water evaporation [7] or deposition of volcanic

aerosols [8]. GPR could define the occurrence of these sediments:

Locally varying deposits would support a groundwater source while

uniform, discretely layered accumulations imply fallout of aerosols.

Second, models for atmospheric evolution suggest considerable

carbonates should have formed in the regolith [9]; however, minimal

concentrations are observed telescopically [10]. Identification of

calcic soils at Meteor Crater implies similar horizons would be

detected on Mars if near the surface. Third, occurrence of nearsurface brines has been proposed and subsequently questioned

[11,12] and models for the latitudinal distribution of ground ice/

water (e.g., [13]) are in wide use. GPR mapping of lateral and depth

variations in dielectric constant could test such models. Finally, GPR

transects could help identify optimal coring locations and might

reveal buried volcanic flows, superposed ejecta deposits, paleosoils,

or regolith depth. In the absence of groundtruth, GPR should define

shallow stratigraphic complexity, thereby providing a context for

interpreting data from other instruments.

Mars landing and GPR deployment proximal to thick unconformable deposits or within the northern lowlands would allow additional

questions to be addressed. Unconformable deposits can accumulate

by volcanic and eolian processes and may relate to accumulation
LPI Technical Report 92-07, Part 1 7

during intervals of polar wandering or more equable climate [1].

GPR transects would identify layering in the deposits and any lateral

variations in thickness. Accumulation during element or polar

climate epochs should be sensitive to orbital forcing, thereby resulting in continuously layered stacked sequences. By contrast, volcanic

processes [2] might produce less continuous, variably thick layers

separated by intereruption paleosoils.

Formation of the northern lowland surface has been attributed to

alluvial, volcanic, eolian [3], and, more recently, pelagic deposition

[4]. Each process produces characteristic stratigraphy that should be

distinguishable with the GPR. For example, debris flows would form

poorly sorted and crudely layered deposits, whereas other fluvial

deposits may be better sorted, more uniformly bedded bar and swale

features. Stratigraphy in both types of alluvium would be limited in

lateral extent. Conversely, pelagic deposition would form wellsorted, fine-grained continuous deposits devoid of bedforms and

possibly interbedded with turbidites. Volcanic and eolian beds can be

similarly characterized. Based on the ease in identifying differing

depositional units with GPR in terrestrial settings (Figs. 1 and 2),

such formations might also be distinguished on Mars.

GPR data collected around terrestrial impact craters discriminates in situ bedrock, ejects, alluvium, and calcic soils, thereby

highlighting the potential of the instrument in a variety of planetary

settings. Inclusion of a GPR on a Mars rover would define shallow

stratigraphy and could map changing dielectric constants in the

substrate if accompanied by groundtruth. In turn, this information

could be used to identify compositional units and help constrain

interactions between surface and atmospheric processes.

References: [1] Schultz P. H. andLutz A.B. (1988)/earns, 73,

91-141. [2]ScottD.H.andTanakaK.L.(1982).7GK,S7,1179-1190.

[3] Greeley R. and Guest J. E. (1987) USGSMapI-1802-B. [4] Parker

T. J. et al. (1989) Icarus. 82. 111-145. [5] Pilon J. A. et al. (1991)

JGR, 96, 15563-15576. [6] Grant J. A. and Schultz P. H. (1991)

LPSC XXIII, 481^82. [7] Toulmin P. et al. (1977) JGR, 82,

4625^1634. [8] Settle M. (1979) JGR, 84. 8343-S354; Grant J. A.

and Schultz P. H. (1992) JGR, in review. [9] Fanale F. P. et al. (1982)

Icarus, 50, 381^107. [10] Blaney D. L. and McCord T. B. (1990)

LPSCm97-98.[ll]ZentA.P.etal.(1990)./Gfl.95,14531-14542.

[12] Huguenin R. L. et al. (1986) Icarus. 68. 99-119. [13] Fanale

F. P. et al. (1986) Icarus. 67, 1-18.

ANALOGUEOFHAND-HELDLENSANDOPTICALMICROSCOPE FOR MARTIAN IN SITU STUDIES. Petr Jakes, Lunar

and Planetary Institute, 3600 Bay Area Boulevard, Houston TX

77058, USA.

The simple hand-held lens (magnification lOx) has been one of

the most powerful tools for the examination of rocks and minerals

over past centuries. In the terrestrial environment the determination

of mineral phases by optical devices (microscopes), combined with

the observation of textural relationships of phases and bulk mineral

composition, usually precedes the use of sophisticated techniques

such as electron microscopy, isotope analysis, etc.

The suggested instrument is a modified optical microscope that

uses aCCD digital camera equipped with microscope optics and LED

illumination. The microscope-camera is capable of providing an

optical "visible light image" of the surface in an area of approximately 4 cm2

 with high resolution (at maximum magnification and

hence smaller area) in the range of 0.005 mm. Deep-focus image

array uses the potential of computer image processing to produce

pseudo-SEM images.

The instrument complements remote sensing and spectral data in

determining the phase composition of particles and their morphological features. The microscope is complemented by an analyzing

instrument that combines the optical tool with the source of X-ray

radiation and an X-ray-sensitive detector in order to perform in situ

semiquantitative chemical analysis of particles in the view of the

microscope.

The idea of a deep-focus imaging instrument uses movable focus

optics (either continuous and/or step by step) to provide a series of

images of the same object with different focus levels. The images of

the same object are computer processed to obtain a deep-focus view

(pseudo-SEM image) of surface particles, thus extending the identification capabilities of the instrument. The computer processing uses

techniques available for image processing of, e.g., aerial photography.

The power of observation of the human eye, which may seem at

present too unsophisticated, should not be omitted in any future

martian mission and should not be unjustly replaced by highly

sophisticated techniques. The planetary processes, either endogenous or exogenous, are recorded in both chemical composition and

rock textures. Soils and regoliths record the history of exchange of

energy/material between the planet's surface, atmosphere (hydrosphere), and surrounding space in the shapes and arrangement of

surface particles. The available data on the martian surface come

from several independent observations: (1) remote sensing techniques such as infrared and near-infrared spectra, (2) analytical XRF

data from two Viking landing sites, (3) visual analysis of surface

features on a scale from a few centimeters up to features thousands

of kilometers in size, and (4) the established common wisdom that

SNC meteorites were derived from the martian surface. Though it

seems that data are plentiful, the speculations on processes involved

in the formation of the martian surface are still little constrained (see

abstracts in Workshop on Chemical Weathering on Mars, LPI

Technical Report 92-04, Part 1). If an instrument providing close-up

views of the surface with submillimeter-scale resolution had been

available on the Viking lander missions, the present-day models of

the phase composition of the martian surface would be much less

speculative.

The early attempts to obtain close-up "visible light" images of

planetary surfaces with fine (centimeter- to millimeter-sized) resolution were not always considered successful by the scientific

community. Apollo 11 stereophotography, Viking-Mariner closeups of Mars' surface, and close-up images of Venus' surface by

Venera 13 and 14 were not as impressive as "aerial" images of large

areas of the planets. Therefore, some reservations on the employment of "microscope techniques" exist. The resolution in the early

images was (except for Apollo 11) at best around 1 cm and the

presence of other data (e.g., chemical analyses) has overshadowed

the value of images. The use of wavelengths other than visible light

with even worse resolution (e.g., reflectance spectra, IR spectroscopy) were multiply interpreted.

Optical imagery will contribute to phase identification and characterization of particle shape. The close-up look at the martian

surface, however, is fully justified. It will complement the knowledge of chemical compositions of the martian surface and will allow

more precise interpretation of exogenous processes.
8 Workshop on Innovative Instrumentation

DEVELOPMENT OF A MOSSBAUER BACKSCATTERING

SPECTROMETER, INCLUDING X-RAY FLUORESCENCE

SPECTROSCOPY, FOR THE IN SITU MINERALOGICAL

ANALYSIS OF THE MARS SURFACE. G. Klingelhofer,

J. Foh, P. Held, H. Jager, R. Teucher, and E. Kankeleit, Inst. f.

Kernphysik, TH Darmstadt, Schlossgartenstrasse 9, D-6100

Darmstadt, Germany.

The element iron is abundant on the surface of Mars (-13% by

weight), as was determined by X-ray fluorescence analysis during

the Viking mission in 1976. But the type of Fe oxides and silicate

minerals is not known. Therefore, for the in situ mineralogies!

analysis of the Mars surface (soil as well as rocks),

 57Fe Mossbauer

spectroscopy is an obvious choice [1].

Mossbauer spectroscopy is a nuclear technique, measuring the

electric and magnetic hyperfine interaction of the nucleus with its

atomic surrounding. The hyperfine interaction leads to an energy

shift of the nuclear states and/or a splitting caused by magnetic or

electric fields. It depends strongly on crystal structure, chemical

bonding, temperature, crystallite size, etc. Thus, by Mossbauer

spectroscopy (MS) the mineralogical composition, its physical and

chemical properties, especially the charge state of the Mossbauer

isotope, the size of small particles, and the magnetic properties of the

sample can be determined, which is of fundamental interest in the

investigation of the martian surface.

The hyperfine splitting is measured by resonance scattering (or

absorbtion) of low-energy y-quanta in the sample. The magnitude of

resonant scattering of these y-quanta (14.4 keV in the case of

 57Fe)

is measured as a function of a defined energy shift (—» Mossbauer

spectrum), produced by the Doppler effect, e.g., a defined velocity

of the y source.

Using a backscattering geometry, the soil and the rocks can be

studied as found; no sample preparation is necessary, A preliminary

construction scheme of our spectrometer is given in Fig. 1 and in [2],

which is similar to a system proposed by a U.S. team [7].

The main parts are the electromechanical vibrator [3,5] mounted

in the center of the instrument, the detector system consisting of

silicon-PIN-diodes, the electronics for the drive and the detectors,

and the

 57Co Mossbauer source. The control and data handling is

done by a transputer (microprocessor) [4]. The total weight of the

system is less than 400 g, with a maximum power consumption

<1.5 W. The total volume will be below 700 cm3 (comparable to a

Coca-Cola can).

lYanspuler board.

Drive electronics

A -B

The instrument allows the recording of Mossbauer spectra using

the backscattered 14.4-keV y-quanta, and the 6.4-keV Fe X-rays,

emitted after internal conversion of the 14.4-keV Mossbauer state.

Because of the different escape depth of these two types of photons

we expect some (limited) depth resolution. Because of low intensity

of the Mossbauer signal the shielding between source and detector

should be sufficient to optimize the signal-to-noise ratio. The elastic

and inelastic nonresonant scattering of the 14.4-keV quanta in the

samplemay significantly affect the signal-to-noise ratio. Because of

its angle dependence the geometry of the detector arrangement has

to be considered very carefully. The surface roughness (or the albedo

of the surface in the 14.4-keV region) also has an influence on the

signal-to-noise ratio.

For interpretation of the Mossbauer spectra it is of interest to

measure the spectra as a function of temperature, and also to

determine the elemental composition of this sample (soil, rock).

Different Fe compounds show different temperature dependences of

HFI. Because an active cooling of the sample does not seem possible,

we want to measure MS spectra as a function of the martian surface

temperature, which varies between about +20° C and -80° C (day and

night, depending on the landing site).

By measuring the X-ray fluorescence (XRF) radiation, excited in

the sample mainly by the 6.4-keV X-rays, 14.4-keV, and 122-keV y

rays emitted from the

 57Co Mossbauer source, the chemical composition of the sample could be determined. For example, the shape of

the Mossbauer spectrum of a-(Fe1.JTix)2O3 depends strongly on the

Ti content and also on the crystallite size [1]. Small magnetic

crystallites are often found to be superparamagnetic. Knowing the Ti

content in the sample, the influence of these two effects could be

distinguished.

For XRF the energy resolution of the PIN diodes, used for

Mossbauer spectroscopy, has to be improved or another type of

photon detector has to be used, for example, HgI2 [8,9].

Another interesting point is the investigation of the martian

surface as a function of depth. This could be done by using the 14.4-

and the 6.4-keV radiation (see above), and also, in the case of the

Mars '96 mission, by using the possibility of digging with the wheels

of the rover, which will be placed on the surface of Mars [1,2].

Using a prototype of the setup shown in Fig. 1, but with only one

diode, we have recorded MS spectra at 14.4 keV for a sample

containing about the same amount of iron as found on the Mars

surface by Viking (Mars sample analogue). From these measurements we conclude that spectra with sufficient statistical quality can

be recorded within about a few hours using a fully equipped

spectrometer.

References: [1] Knudsen J. M. et al. (1992) Hyp. Int., 68, 83.

[2] Klingelhofer et al. (1992) Hyp. Int., 71, 1449. [3] Kankeleit E.

(1975) Proc. Intl. Conf. on Mossbauer Spectroscopy, Vol. 2,43-58,

Institut fur Kernphysik, TH Darmstadt, Germany. [4] Baltes P.

(1990) GSI Scientific Report, 346. [5] Kankeleit E. (1964) Rev. Sci.

Instr., 35, 194-197. [6] Shelter T. D. et al. (1991) LPSC XXII.

[7] Agresti D. G. et al. (1992) Hyp. Int., 72,285. [8] Iwanczyk J. S.

(1990) IEEE Transactions on Nuclear Science, Vol. 37, 198.

[9] Economou T. et al. (1990) LPSC XXI.

Fig. I. Mossbauer backscattering spectrometer.
LPl Technical Report 92-07, Pan 1 9

MAGNETIC PHASES ON THE MARTIAN SURFACE. J. M.

Knudsen1 and L. Vistisen2, 'Physics Laboratory, H. C. 0rsted

Institute, Universitetsparken 5, DK-2100, Copenhagen 0, Denmark,

2Niels Bohr Institute, Blegdamsvej 17, DK-2100, Copenhagen 0,

Denmark.

The Viking landers on Mars were equipped to detect magnetic

particles, and a remarkable finding was that the martian soil adhered

nearly equally well to both strong and weak magnets on board the

landers [1]. It was concluded that every particle making up the dust

contained 1—7% of a strongly magnetic mineral. The nature of the

magnetic mineral in the martian soil is not known with certainty.

The SNC meteorites, believed to come from Mars, contain a

ferrimagnetic phase (titanomagnetite). Magnetic fractions of the

meteorites Nakhla and Zagami have been studied by Mossbauer

spectroscopy. The magnetic properties of the two meteorites, i.e.

saturation magnetization, Neel point, etc., are very different, but

both Zagami and Nakhla contain titanomagnetite. If SNC meteorites

are indeed martian surface rocks, it seems reasonable to conclude

that the surface basalts of Mars contain a magnetic phase. This is

assumed in the following.

As both the soil and the rocks contain magnetic phases, it is

evident that instrumentation for the study of magnetism on Mars is

significant.

Soil: There are several possibilities for the origin of the

magnetic phase in the soil. Let us mention two (certainly not the only

ones). (1) The magnetic phase could have formed as a weathering

product, inherited directly from the underlying basaltic base rock. In

that case the phase would probably contain titanium [2]. (2) The

magnetic phase could have formed via precipitation of Fe(HI)

compounds in liquid water. In that case the phase will probably be

rather pure y-Fe2O3 or Fe3O4.

The various chemical pathways thus lead to a somewhat different

structure and composition of the magnetic phase, and we may leam

about the evolution of the surface of Mars through the identification

X Abs.

0.0 .

2.0 .

4.0 .

6.0 J

0.0 .

2.0 .

4.0 .

6.0 .

V1m

-10 -8-6-4- 2 0 2 4 6 8 10

Velocit y (mm/s)

of the phase. The identification of the magnetic mineral would be a

simple matter in the laboratory, difficult but perhaps possible

through robotic experimentation on Mars.

By means of Mossbauer spectroscopy it will be possible to

distinguish between maghemite and magnetite [3,4]. It may, however, be problematic from a Mossbauer spectrum alone to decide if

the phase in question contains titanium as impurity. This may

possibly be done by means of a simple piece of instrumentation

described below.

Instrument for Measurement of Magnetic Properties: During the Viking mission, magnets to study both the surface soil and

airborne dust were successfully applied. A simple extension of the

Viking experiment would involve a disc with a number of magnets

that would produce different magnetic fields and field gradients at

the disc surface. With an array of, say, eight magnets it should be

possible to determine a saturation magnetization within a factor of 2.

Furthermore, if the dust at the disc of magnets could be heated, for

instance by means of a simple parabolic mirror reflecting (and

concentrating) the sunlight on the dust adhering to the magnet, it

would be possible to determine (approximately) at which temperature the dust falls off the magnets. If this is accomplished, and a

Mossbauer spectrum of the dust is available, the magnetic phase in

the martian fines has been identified.

Figure 1 illustrates the application of Mossbauer spectroscopy to

the study of a terrestrial red tropical soil from Brazil [5]. The letter

V is for classification. The spectrum marked Vim is the Mossbauer

spectrum of a sample prepared from VI by magnetic separation.

This Brazilian soil has about the same magnetic properties as the

martian soil. The phase responsible for the magnetism of the

Brazilian soil is titanomaghemite, with the approximate composition

(Fe075Ti025)[Fe12sTi025n0j]O4, ( ) tetrahedral sites, [ ] octahedral sites, D vacancies. A magnetic separation will not be possible

on Mars, but even without separation the magnetic phase may, from

the Mossbauer spectrum on Fig. 1, be clearly identified as maghemite.

It is, however, not possible to infer the titanium content. Pure

maghemite transforms to hematite at 320°C. By measuring the

approximate value of the saturation magnetization by means of the

disc of magnets, and by measuring the temperature at which the dust

falls off the magnets, it may be possible to give a rough estimate of

the titanium content of the sample.

Complications: If it is decided to include the suggested disc

(and heating procedure) in the payload of a spacecraft to Mars, many

simulation experiments have to be done. The magnetic properties of

titanomaghemite—and maghemite with other isomorphous substitutions (Al, Mn, etc.)—are complicated, and the stability of

maghemite containing impurities has to be investigated extensively.

Magnetic Phase in the Base Rocks on Mars: The fact that

SNC meteorites contain a ferrimagnetic phase promises a rich field

of paleomagnetic investigations on Mars if the planet ever generated

a global field. New instrumentation for this activity has been

described elsewhere [6].

References: [1] Margraves R. B. et al. (1977) JGR, 82.

4547^1558. [2] Coey J. M. D. et al. (1990) JGR, 95, 14423-14425.

[3] Knudsen J. M. et al. (1991) Hyp. Int.. 68.83-94. [4] Klingelhofer

G. et al., this workshop. [5] Allan J. E. M. et al. (1988) Phys. Chem.

Minerals, 15, 470-475. [6] Nielsen O. V. et al. (1992) JGR, 97,

1037-1044.

Fig. 1. Transmission Mossbauer spectra at room temperature for a sample

from Brazil. From [5].
10 Workshop on Chemical Weathering on Mars

MASS SPECTROMETRIC STUDIES OF THE INTERACTION OF MARTIAN ATMOSPHERE GAS COMPONENTS

WITH FERRIC OXIDE SURFACE UNDER UV ILLUMINATION. A. P. Koscheevi and L. M. Mukhin2

 HCarpov Institute

of Physical Chemistry, Moscow, Russia,

 2Space Research Institute,

IKI, Moscow, Russia.

Photostimulated interaction of gases with metal oxides could be

interesting for the problem of photochemical weathering on Mars.

The martian rocks contain some photoactive oxides such as Fe2O3,

TiO2, etc., and there is enough UV radiation at the martian surface to

stimulate the gas-surface reactions.

We have used mass spectrometry and thermodesorption spectroscopy methods to study some aspects of interaction of H2O, CO2, CO,

and O2 and their mixture with the surface of Fc2O3 powder in the dark

conditions and under UV illumination at temperatures 200-300 K

and pressures 10-MO-* Torr.

In the dark conditions the chemisorption of CO2 and H2O was

observed and these molecules can be removed from the surface of

Fe^ only by heating or by U V irradiation. We have observed the

blocking effect of preadsorbed H2O molecules on adsorp tion of CO2.

The adsorbed H2O molecules also caused the appearance of a new,

tightly bound state of adsorbed CO2 and the filling of this new state

may be increased by UV illumination.

The adsorbed CO molecules do not desorb as CO from the Fe2O3

surface. The only product of thermo- and photodesorption observed

in this case was CO2 and the efficiency of CO2 photostimulated

formation from CO on Fe2O3 surface was increased with surface

oxygen concentration. Some aspects of catalytic oxidation of CO on

the Fe2O3 surface under illumination were studied.

The experimental results are discussed in terms of CO2-H2O, COOj.,, and CO-O^jj surface complex formation and in terms of their

behavior under UV illumination.

DOES UV INSTRUMENTATION EFFECTIVELY MEASURE

OZONE ABUNDANCE? Bernhard Lee Lindner, AER, 840

Memorial Drive, Cambridge MA 02139, USA.

Measurements of O3 on Mars provide significant information

about the chemistry and composition of the atmosphere [1], including long-term changes [2]. The most extensive and accurate data

were inferred from the Mariner9 U V spectrometerexperiment, some

of which are reproduced in Fig. 1. Mars O3 shows strong seasonal and

latitudinal variation, with column abundances ranging from 0.2 (imatm at equatorial latitudes to 60 pm-atm over the northern winter

polar latitudes [1] (1 (om-atm is a column abundance of 2.689 x 1015

molecules cnr2).

The Mariner 9 U V spectrometer scanned from 2100 to 3500 A in

one of its two spectral channels every 3 s with a spectral resolution

of 15 A and an effective field-of-view of approximately 300 km2.

Measurements were made for almost half a martian year, with winter

and spring in the northern hemisphere and summer and fall in the

southern hemisphere. The detectability limit of the spectrometer was

approximately 3 (Om-atm of ozone. The process used by earlier

investigators to extract the ozone abundance from the observed

Mariner 9 spectra is as follows [1]. Each spectrum was filtered to

remove spurious data points, then compared to the solar flux spectrum and shifted slightly in wavelength in order to compensate for

any systematic shift in the wavelength calibration of the spectrometer. Incoming solar radiation was assumed to undergo Rayleigh

scattering by CO2 and Mie scattering by the polar hood, and to be

LATITUDE (deg)

Fig. 1. Measurements of the O3 column abundance inferred from the Mariner

9 UV spectrometer data during the northern winter, Ls = 330-360, in the

northern hemisphere (see [2]).

z

UJ

H

Z

ORBIT 144

UV SPECTRUM AT °B"

57«N

2100 2500 3000 3500

WAVELENGTH (

Fig. 2. Ultraviolet spectrum measured by Mariner 9 at 57N latitude on orbit

144. To enhance the O3 absorption feature, this spectrum was divided by one

obtained at 20N latitude on orbit 144, where O3 abundances are minimal [1 ].

reflected by a wavelength-independent surface albedo. The only

atmospheric absorption in the 2000- to 3000-A region was assumed

to come from the Hartley band system of ozone, and therefore the

amount of ozone was inferred by fitting this absorption feature with

laboratory dataof ozone absorption, as shown in Fig. 2.03 absorption

of sunlight is not strong enough to affect atmospheric temperature on

Mars [3], and hence cannot be inferred from temperature measurements.

I use a radiative transfer model based on the discrete ordinate

method to calculate synthetic radiance spectra. Figure 3 shows that

when typical amounts of dust and cloud are present, significant

underestimation of O3 occurs. A factor of 3 times as much O3 is

needed to generate the same spectrum as for a clear atmosphere. If
LPl Technical Report 92-07, Part 1 \ \

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00 2400 2700 3000 33(

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1.5

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00 2400 2700 3000 3300

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Fig. 3. Synthetic spectra as would be observed by spacecraft for atmospheres

with (a) no cloud or dust and 30 mm-atm O3, (b) vertical opacities of dust and

cloud of 0.3 and 1.0 respectively and 30 mm-atm of O3, and (c) vertical

opacities of dust and cloud of 0.3 and 1.0 respectively and 100 mm-atm of O3.

All cases assumeasolarzenith angleof 75 (typical for winter polarobservations)

and viewing angle of 60, with azimuth angle of 0 (typical for Mariner 9). Polar

cap albedo of 0.6.

the scattering properties of m artian clouds and dust were well known,

then their appearance would not be a problem, as a model would be

capable of retrieving the O3 abundance. However, these properties

arenot well known, which raises doubts about the effectiveness of the

current UV spectroscopy technique used to measure O3.

Spatial and temporal variability in temperature and water vapor

have been claimed to account for the scatter of the data points in Fig.

1 [4]. A decrease in temperature would result in a decrease in water

vapor, if saturated as expected at prevalent temperatures. A decreased water vapor abundance decreases the availability of odd

hydrogen, which converts CO and O into CO2 catalytically, decreasing the abundance of O needed to form O3. However, water vapor is

a small source of odd hydrogen in the winter polar atmosphere, and

may not account for most of the variability in Fig. 1 [5]. Masking by

clouds and dust may also account for some of the observed O3

variability, because the nature and opacity of the clouds and dust in

the polar hood change dramatically in latitude and even on a day-today basis. As the maximum O3 abundance resides near the surface

[5], spacecraft must be able to observe through the entire cloud and

dust abundance in order to actually see the total O3 column abundance. If reflectance spectroscopy is used, as on Mariner 9. then the

cloud and the airborne dust must be traversed twice, first by the

incoming solar flux down to the surface and then once again upon

reflection from the surface out to the spacecraft. In addition, the large

solar zenith angles at winter polar latitudes mean several times the

vertical opacity of cloud and dust must be traversed. Indeed, part of

the observed latitudinal variation in O3 in Fig. 1 may be due to the

inability of the spacecraft to observe through the increasing effective

optical depths as one goes poleward.

The UV spectrometer on Mariner 9 was incapable of penetrating

the dust during dust storms [1]; the single-scattering albedo and

phase function of airborne dust and cloud ice are not known to the

degree required to extract the small UV signal reflected up from near

the surface. The reflectance spectroscopy technique would also have

difficulty detecting the total column abundance of O3 in cases where

large dust abundances exist together with the polar hood, especially

at high latitudes where large solar zenith angles magnify those

optical depths; yet these cases would contain the maximum O3 based

on theoretical results [5]. It is quite possible that the maximum O3

column abundance observed by Mariner 9 of 60 pm-atm is common.

In fact, larger quantities may exist in some of the colder areas with

optically thick clouds and dust. As the Viking period often had more

atmospheric dust loading than did that of Mariner 9, the reflectance

spectroscopy technique may even have been incapable of detecting

the entire O3 column abundance during much of the Mars year that

Viking observed, particularly at high latitudes.

Acknowledgments: I acknowledge support under contract

NASW-4614.

References: [1] Lane A. L. et al. (1973) Icarus, 18,102-108.

[2] Lindner B. L. and Jakosky B. M. (1985) JGR, 90, 3435-3440.

[3] Lindner B. L. (1991) Icarus, 93. 354-361. [4] Earth C. A. and

Dick M. L. (1974) Icarus, 22. 205-211. [5] Lindner B. L. (1988)

Planet. Space Sci., 36, 125-144.
12 Workshop on Chemical Weathering on Mars

IN SITU IDENTIFICATION OF THE MARTIAN SURFACE

MATERIAL AND ITS INTERACTION WITH THE MARTIAN ATMOSPHERE USING DTA/GC. R. L. Mancinelli and

M. R. White, NASA Ames Research Center, Moffett Field CA

94053, USA.

Little is known about the mineralogy of the martian surface

material. Several techniques have been suggested as candidates for

the in situ identification of the martian surface material. The most

promising of these techniques include differential thermal analysis

(DTA) coupled with gas chromatography (GC) and differential

scanning calorimetry (DSC) coupled with either mass spectrometry

(MS) or GC. Our studies have shown that differential thermal

analysis coupled with gas chromatography (DTA/GC) is a more

appropriate analytical technique than DSC/MS or DSC/GC to identify the mineralogy of the martian surface material in situ [1]. DTA/

GC can be regarded as an advancement from pyrolytic GC analyses

that have been successfully flown on previous missions, but have

supplied only limited mineralogical information [2].

Coupling a DTA with a GC enables one to identify and quantify

gases that evolve during the heating process (e.g., organics, CO2,

H2O, etc.), and allows one to correlate the thermal events on the DTA

with the specific gases evolved during that event. This allows one to

characterize samples. This characterization allows the distinction to

be made among a variety of mineral classes (e.g., clays, zeolites, and

silicates, degrees of hydration, CO3

2

-, NO3~, etc.).

The development of a prototype flight instrument is based upon

criteria developed using laboratory equipment To define the flight

experiment, laboratory analyses were conducted using a Dupont

model 1600 high- temperature DTA oven equipped with a model 910

cell base. Typically, 30 mg of sample was analyzed and 30 mg of

A12O3 served as the reference. The chamber was sealed, and the

analysis performed under a vacuum. The system is controlled by a

Sun Spare n workstation. The interface between the DTA and the GC

consists of a stainless steel tube, equipped with pressure sensors,

leading to the GC sampling valve. If during the heating process gas

evolves, it is sensed by the pressure sensors, which trigger a valve

allowing the gas to be expanded from the oven chamber into a GC

sample loop for GC analysis. The Sun then automatically injects the

sample onto the GC column and resets the system for another event.

en

E

O

Temperature (°C)

en

E

O

Temperature (°C)

Fig.2. DTA signatures for (a) a 1:1 mixturcofmontmonlloniteandkaolinite

and (b) Fe-enriched monunorillonite.

12-1

200 400 600 800 1000 1200

Temperature CO

Fig. 1. DTA signature and concomitant pressure sensor readings for the

analysis of an evaporile from Yellowstone National Park, Wyoming.

When a gas is evolved during a thermophysical event, the

temperature is recorded such that the evolved gas is temperaturestamped so it can be associated with a specific thermal event to the

nearest degree. For example, the analysts of an evaporite collected

from Yellowstone National Park, Wyoming, reveals that at ~800°C

an endotherm occurs that is associated with the release of a gas

(Fig. 1), identified as CO2. The sample identification software yields

an identification of the sample and the probability of its accuracy. For

this analysis the sample was identified as aragonite and calcite with

a probability of 99%.

Because it has been suggested that clays may be an important

component of the surface of Mars [4], their identification during in

situ experiments will be important. Examination of the DTA signature for a 1:1 mixture of Crook County, Wyoming, montmorillonite

and kaolinite from Washington County, Georgia, (KGa-1) (Fig. 2a)

reveals that the two clays can be easily distinguished by their

dehydroxylation exotherms (550°C for kaolinite and 700°C for

montmorillonite) and high-temperature transition exotherms (970°C

for montmorillonite and 1020°C for kaolinite). The difference in the

high-temperature transition is key in distinguishing a variety of clay s
LP1 Technical Report 92-07. Part j 13

from each other using the DTA. Figure 2b depicts Fe-enriched

montmorillonite clay prepared by the procedure of Baninetal. [3,4].

The endotherm occurring at 280°C is due to the dehydroxylation of

lepidocrocite (y-FeOOH) to y-FejC^ (maghemite) and is accompanied by dehydroxylation and the formation of H2O vapor. The

exothermic peaks observed at 321 °C, 430°C, and 590°C are due to

the transition of y-Fe2O3 —» ct-Fe^ (hematite). The differences in

temperature are due to particle size differences. In general, the limit

of detectability for amineral or organic compound in the DTA is ~1 %

(wt/wt) [5].

References: [1] Mancinelli R. L. et al. (1992) Adv. Space Res.,

12. 111-116. [2] Biemann K. et al. (1977) JGR. 82, 4641-4658.

[3] Banin A. (1973) Quantitative ion exchange process for clays.

U.S. Patent Nd 3.725,528. [4] Banin A. et al. (1988) Origins of Life.

75,239-265. [5] Mancinelli R. L.etal. (1992)LPSCXX///,831-832.

ATMOSPHERIC IMAGING FROM MARS LANDED

STATIONS. Terry Z. Martin, Jet Propulsion Laboratory, Mail

Stop 169-237.4800 Oak Grove Drive, Pasadena CA 91109, USA.

A wide variety of information about atmospheric phenomena at

the surface of Mars can be obtained with imaging systems on landed

stations. I discuss here the range of such observations and their

requirements.

Atmospheric Opacity: Determination and History: Dust

opacity is central to the meteorology of Mars through its effect on the

absorption of sunlight This parameter may be used, as with Viking

Lander imaging data, to infer global behavior, although we know that

there are strong areal variations in the distribution of dust and ice

clouds. The opacity indicates the effect of dust storms and the column

abundance of one form of water, given separation of dust from ice

opacity by diurnal variation or filter capability.

Determination of opacity can be done with very simple optical

detectors such as adiode and a hemispheric window. However, given

an imaging system, the problem is that of imaging the Sun (or

Phobos, or a star) directly, or a calibration target illuminated by the

Sun. Nighttime opacity measurements can be particularly important

for fog detection and studying dust settling. Calibration targets are

not ideal for opacity measurement because they can collect dust

when oriented upward.

The frequency of measurement for opacity depends on the causal

mechanism. Local dust storms can raise dust in minutes; it would be

of great value to observe this phase from a lander. High-frequency

observations can be triggered by other data, like wind speed. Global

storms would cause much slower changes, so that daily measurements might suffice. Water ice variations seem to be diumally

induced, indicating hourly observations.

Atmospheric Aerosols: Physical Properties: Greater angular

resolution allows going beyond total optical depth to obtain information about the size and distribution of airborne particles; the information is contained in the scattering phase function. The sky brightness

should be measured as a function of distance from the solardisk, with

an accuracy and resolution of about 1°. For phase function measurement, there is much redundancy in an image of the sky. A parameterization of the intensity contours of an image would be adequate if

internal instrument scattering effects can be removed.

Separation of the dust and ice components of the atmosphere can

be done by observing diurnal variation of the scattering behavior and

using a variety of spectral filters.

Observations of the sky near sunrise and sunset can provide

unique information about the vertical distribution of paniculate

matter, since the sunlight's path is constrained by the planet's edge.

The increased path to the Sun through the atmosphere also serves to

magnify color effects produced by particulates.

Clouds: Detection and Tracking: Individual clouds are common in orbital images of Mars; these arise from topographic or polar

edge effects, from regional circulation behavior, or local turbulent

phenomena such as dust devils. CO2 ice clouds in the winter polar

caps are also inferred from IR measurements. Stations on the martian

surface offer unique opportunities to observe these clouds: The

observing site is fixed and chosen; the spatial scale is small; and the

geometry is unique.

A fixed observing site means that an individual cloud can be

tracked over a longer period of time than a typical orbiter can devote

(although both approaches are desirable). Clouds, of course, act as

wind indicators, including winds at levels the lander cannot sample

directly. A site can, in principle, be chosen partly for the cloud

phenomena known to be found there (fogs, lee wave clouds, dust

activity). The landed station can observe phenomena that would be

too small to discern in large-scale imaging data: dust devils, other

gust-induced dust storms, and small fog banks. Finally, the lander

geometry provides observation at high phase angles that are especially suitable for detection of thin clouds. The depth of fogs can be

established far more easily from a lander than from orbital altitudes.

It should be mentioned that one particular observation mode

employed by the Viking cameras, in which the same vertical line was

repeatedly scanned, has special value for atmospheric observations.

Clouds passing through the field, as well as the changing brightness

of the sky as the Sun moves, can be recorded. This mode of

observation is relatively conservative of data rate.

It seems particularly appropriate for a mission addressing meteorology that the surface stations, spread widely over the surface, also

devote time to looking directly at the atmosphere. The synergism

possible is important. For example, consider the value of imaging

observations triggered by detection of wind gusts that might raise

dust locally. Similarly, recording could be stimulated by a

hygrometer's indication of the presence of fog.

It is also possible for atmospheric imaging to affect the course of

other investigations. The presence of clouds can alter the color of

rocks. Cloud motions can corroborate wind measurements. Opacity

data can influence the choice of times to collect samples (to avoid or

select dust deposition effects).

One particularly interesting case of surface and atmospheric

objectives coming together is the observation of small-scale wind

streaks—surface phenomena caused by the wind. There is every

reason to believe that scouring and deposition act on the small scale

seen by a landed station, as well as on the familiar large scale.

Locating a station in an area known to experience large seasonal

changes would open up the possibility of measuring the characteristics of blowing dust, thus corroborating the models built up over

many years by Greeley and coworkers.

An all-sky camera would ideally satisfy atmospheric science

objectives. However, a camera designed for surface science will also

be of value for atmospheric science if it can (1) point above the

horizon (minimum requirement); (2) sample phase angles approaching 180° (better); (3) point at the Sun (best); (4) remove internal

scattered light effects through calibration; (5) provide images over a

range of visible band wavelengths; or (6) provide sensitivity adequate to image Phobos or bright stars.
14 Workshop on Chemical Weathering on Mars

N

MASS SPECTROMETER -PYROLYSIS EXPERIMENT FOR

ATMOSPHERIC AND SOIL SAMPLE ANALYSIS ON THE

SURFACE OF MARS. Konrad Mauersbergeri, Paul Mahaffy2,

and Hasso Niemann2, iSchool of Physics and Astronomy, University

of Minnesota, 116 Church St. S.E., Minneapolis MN 55455, USA,

2Code 915, NASA Goddard Space Flight Center, Greenbelt MD

20771, USA.

Introduction: Results from the Viking mission will form the

foundation for future in-depth investigations of atmosphere-surface

interactions on Mars. The two Viking landers carried impressive

instrumentation to obtain and analyze soil samples: The sites were

observed by cameras, and the collector head was located on a long

boom and allowed the collection of large samples at various depths.

A selection of grain sizes was possible and a distribution system

supplied a number of experiments with soil material. Despite stationary vehicles, a wide sampling field was reachable. The GCMS

system, responsible for atmospheric as well as surface soil analysis,

worked well on both landers. Atmospheric measurements resulted in

the determination of the abundance of noble gases as well as of other

molecular species. Iso topic composition measurements included the

important ratios of

 13C/12C, 1SN/1

*N, and ^Ar/^Ar. To verify these

past results and to advance detailed studies of noble gas isotope ratios

and minor constituents, better instrument sensitivities, higher precision, and lower background contributions are required in future Mars

missions. Soil analysis during the Viking mission concentrated on

organic material. Heating cycles were performed to 500°C and only

water and carbon dioxide were identified. Higher pyrolysis temperatures are of primary importance to advance our understanding of the

mineralogy and gas loading of surface material and atmospheric

exchange.

Objectives: An experiment is under development that will

combine atmosphericgas analysis with the pyrolysis of collected soil

samples. This paper will focus on the pyrolysis part of the experiment. The design has been guided by the following assumptions:

(1) The system must have the capability for multisample analysis,

(2) the temperature range must exceed 500°C and should reach

1000°C by using an efficient heating system, and (3) the pyrolysis

system with analyzer must be small in size and mass in order to be

considered for a number of future Mars missions.

One of the important science objectives will be the search,

performed by studying characteristic release patterns during heating,

for specific mineral types such as carbonates or sulfates. Within the

temperature range of the pyrolysis process of approximately 1 000°C

nitrates should be released between 300°C and 400°C as NO2,

carbonates near 500°C to 600°C as CO2, and, finally, sulfates will

decompose into SO2, H2S, or others between 800°C and 1000°C.

Isotope ratios of C, O, and S will be determined as the molecules

carrying these elements appear in the mass spectrum.

While a gas chromatograph ahead of the mass spectrometer may

provide a useful separation of complex organics, the proposed

stepwise heating system of the pyrolysis experiment and the expected low abundance of organic compounds does not justify the

additional complexity of a gas chromatograph at the present time. A

mass spectrometer can quickly scan a large mass range to survey

released gases including their time evolution during the pyrolysis

process. In addition, isotope ratios can be measured and enrichment

procedures can be monitored and the products analyzed.

Experiment Description: The present design of the pyrolysis

experiment is based on a small cylindrical unit (~300 cc) that

contains a rotatable disc where 6—8 cells (or crucibles) are located on

its periphery. Each cell is made of sapphire and can accept about

2 cc of soil material. In order to load a cell, it is rotated under an

opening on top of the cylinder, and thereafter is placed into a

stationary oven to start the pyrolysis process. The heating will

proceed in a stepwise or ramp fashion. Assuming each cell is loaded

to about one-half or one-third of its capacity, repeated use of a cell

after the first pyrolysis process (and some additional heating) is

possible.

The evolved gas will be fed into the mass spectrometer, which

will also be used for atmospheric gas analysis. The small quadrupole

gas analyzer has been employed in many previous space experiments

and is characterized by both a high sensitivity and mass resolution.

Discussion: On a broader scale, the pyrolysis experiment actually contains anumber of subsystems that must also be considered for

a space mission. The parts may be subdivided into sample collector,

sample transfer to pyrolysis cells, pyrolyzer, pumping system, gas

transfer, and gas analyzer.

The first two subsystems are difficult to evaluate at the present

time. They depend strongly on the spacecraft configuration and on

the support provided to experiments. On a mission with small

spacecrafts, sample collection and transfer may become a difficult

task. The pyrolysis experiment sketched above was initially designed for a rover containing a sample collector and distributor for

onboard experiments.

The pumping system plays a central role in the operation of the

pyrolysis system and mass spectrometer. In the past, getter and

sputter ion pumps have been used in space missions to evacuate gas

transfer and mass spectrometer systems. Those pumps, however,

may cause interferences with noble gases by outgassing previously

pumped material or by introducing pumping speed-dependent enrichments or depletions. To circumvent those deficiencies, development of a turbomolecular pump has been initiated that will be capable

of operating against the martian atmospheric pressure yet maintaining ultrahigh vacuum conditions inside the attached instruments.

With a mass of about 1 kg and a power consumption of 12 W,

pumping speeds of 10 to 50 1/s should be achieved. Even when

adding the required robustness of space flight equipment, present

technology makes the development of such a small pump feasible.

In summary, a combination of a flight-proven mass spectrometer

with noble gas enrichment cells, a lightweight, low-power turbomolecular pump, and a multicell, high-temperature pyrolysis system

are under development that could provide the next generation of

atmosphere-surface analysis instruments after the Viking mission.

N94-2243 8

TEMPERATURE/PRESSURE AND WATER VAPOR

SOUNDING WITH MICROWAVE SPECTROSCOPY. D. O.

Muhleman1, M. A. Janssen2, R. T. Clancy3, M. Frerking2, S. Gulkis2,

D. J. McCleese2, R. Zurek2, and R. M. Haberle4, 'California Institute

of Technology, Pasadena CA 91125, USA,

 2Jet Propulsion Lab, 4800

Oak Grove Drive, Pasadena CA 91109, USA,

 3

LASP, Washington

University, St. Louis MO 63130, USA, "NASA Ames Research

Center, Moffett Field CA 94035, USA.

Two intense microwave spectral lines exist in the martian

atmosphere that allow unique sounding capabilities: water vapor at

183 GHz and the (2-1) rotational line of CO at 230 GHz. Microwave

spectral line sounding is a well-developed technique for the Earth's

atmosphere for sounding from above from spacecraft and airplanes,

and from below from fixed surface sites. Here we describe two

simple instruments for temperature sounding on Mars (the CO line)

and water vapor measurements. The surface sounder proposed for the

MESUR sites is designed to study the boundary layer water vapor
LPI Technical Report 92-07, Part 1 15

distribution and the temperature/pressure profiles with vertical

resolution of 0.25 km up to 1 km with reduced resolution above

approaching a scale height. The water channel will be sensitive to a

few tenths of a micrometer of water and the temperature profile will

be retrieved to an accuracy between 1 and 2 K. The latter is routinely

done on the Earth using oxygen lines near 60 GHz. The measurements are done with a single-channel heterodyne receiver looking

into a 10-cm mirror that is scanned through a range of elevation

angles plus a target load. The frequency of the receiver is sweep

across the water and CO lines generating the two spectra at about 1-

hr intervals throughout the mission. The mass and power for the

proposed instrument are 2 kg and 5—8 W continuously. The measurements are completely immune to the atmospheric dust and ice

particle loads. We feel that these measurements are the ultimate ones

to properly study the martian boundary layer from the surface to a

few kilometers. Sounding from above requires an orbiting spacecraft

with multichannel microwave spectrometers such as the instrument

proposed for MO by a subset of the authors, a putative MESUR

orbiter, and a proposed Discovery mission called MOES (Sanjey

Limaye, PI). Such an instrument can be built with less than 10 kg and

use less than 15 W. The obvious advantage of this approach is that

the entire atmosphere can be sounded for temperature and water

vapor in a few hours with somewhat better than a scale height

resolution. If a bigger mirror is used (>30 cm) limb sounding

geometry can be employed and half scale height resolution achieved

to altitudes up to at least 60 km. Again, the measurements are

immune to dust and ice loads. Water vapor sensitivity of 0.1 um can

be achieved (even with a nadir instrument) and temperature profiles

retrieved to an accuracy of better than 2 K from the surface to about

60 km. Winds can be measured from the doppler shifts of CO lines

in the limb sounding mode.

PRELIMINARY EXPERIMENTAL RESULTS OF UV

IRRADIATION OF CARBONATES. L. M. Mukhin1, J. Huth1,

H. Wankei, Y. Dikov2, and A. P. Koscheev^. iMax-Planck-Institut

fur Chemie, Mainz, Germany,

 2IGEM, Moscow, Russia, 3Karpov

Institute of Physical Chemistry, Moscow, Russia.

The data on the chemical composition of the martian surface and

atmosphere and the intensity and spectral distribution of solar

irradiation at the surface of Mars lead to the suggestion that photochemical processes can play a significant role in the chemical

evolution of the martian atmosphere and surface. In a number of

experimental papers the potential importance of gas-solid photochemistry for the chemical evolution of the martian atmosphere and

surface has been shown [ 1—5]. However, there is a lack of information about the stability of native minerals under U V irradiaiton. This

problem is important for Mars because the surface of this planet is

open for short wavelength UV with K > 190 nm. In the present work

we investigated the stability of calcite under UV irradiation. Our

experimental set-up is schematically represented in Fig. 1.

The sample of calcite monocrystal with a geometrical surface

area of =1 cm2 was mounted in a vacuum chamber with a sapphire

window, transparent to U V irradiation with X > 180 nm. Prior to UV

irradiation the total pressure in the chamber was higher than

10'7 mbar. The surface of the sample was exposed to U V irradiation

using a 30-W deuterium lamp.

n I \ I

T"T i

1 UV-LAMP

2 SAPHIRE WINDOW

3 SAMPLE CHAMBER

4 VALVE Nl

5 MASS SPECTROMETER

6 VALVE N2

^ PUMP

Fig. 1.

LOWS

ITV-IRRADIATION OF MINERALS

7.0EJJ6

2 «.OE-<XS

: E

~ SJJEXX

o

U 4.0E-86

3J)&0«

2.0M6

O.OE+00

i i

< ; ; •

• A. ALBITE j ! ,

i * BI1ANK •

: • LALCllb ;

• "! i i • I I 1 i i

;

 m ; ' ! i i ! ;

>;..;;; .

!

 : ' I '• ' i !

V A ; : ; ;*;":";- •

: : : : j

0.00 2.00 4,00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 2040

TIME[h]

Fig. 2.

In typical runs the sample was exposed to U V irradiation for about

20 hr. Once every hour the chamber was closed by valve Nl (Fig. 1)

and after 10 min exposition the gas composition in the chamber was

measured by a quadrupole mass spectrometer (Balzers Quadrupole

mass spectrometer QMG 64), valve Nl open, valve N2 closed.

This experimental procedure allowed us to obtain quantitative

data about the partial pressure of a definite gas component, especially

of CO2. In blank experiments the same procedure was used without

a sample as well as with an albite sample.

The effect of evolving CO2 from calcite under U V irradiation was

detected (Fig. 2). The possible explanation of this effect is the

photodestruction of calcite under UV irradiation. If the evolving CO2

is really connected with the photodestruction of carbonate, then a

simple estimation shows that the rate of photodestruction is equal to

2.5 X 1Q-4 nm/s. The blank experiment did not show noticeable CO2

production. The possible application of this effect to martian conditions needs more detailed investigations.
16 Workshop on Chemical Weathering on Mars

References: [1] Tseng S.-S. and Chang S. (1974) Nature, 248,

575-577. [2] Huguenin R. L. (1973) JGR, 78, 8481-8493.

[3] Huguenin R. L. (1973) JGR. 78,8495-8506. [4] Huguenin R. L.

(1974) JGR, 79, 3895-3905. [5] Booth M. C. and Kieffer H. H.

(\91S)JGR,83, 1809-1815.

COMPAS: COMPOSITIONAL MINERALOGY PHOTOACOUSTIC SPECTROMETER. W. Hayden Smith, Washington

University, St. Louis MO 63130, USA.

Science Objectives: Chemical and mineralogical compositions are key data needed for reconstruction of the development

history of the martian crust and of the soils that cover it. Photochemical weathering is an active, important process on Mars, controlling

the nature of exposed rock surfaces. It is necessary to differentiate the

surface weathering products from the underlying base rock. The

weathering process itself is an important consequence of the atmosphere-surface interaction, about which we know little [1]. The

surface patina provides the means to characterize the weathering

process. Penetration of the surface patina is necessary to characterize

the underlying base rock.

Measurement Objectives: There is a critical need for a true

absorption spectroscopic method for in situ rock studies to complement remote sensing by diffuse reflectance spectroscopy. The absorption spectra that are independent of the spectral effects of

scattering, particle size, and distribution provide accurate and reliable diagnostics of rock species. Such a method would be invaluable

for detailed rock-level mineralogy during martian micro- and

minirover missions. Mineralogical knowledge complements elemental data and the visible and infrared spectra provide invaluable

information about the texture of the materials on the martian surface

and about the nature of the weathering processes that have occurred.

Gamma ray measurements from martian orbit suggest that the

chemical signature of the surface is dominated by materials similar

in composition to the materials analyzed at the Viking sites, i.e., of

basaltic affinities [2]. Mars Observer is scheduled to begin mapping

operations late in 1993 and includes a gamma ray spectrometer to

map surface chemistry and a thermal emission spectrometer (TES)

to delineate mineralogy and surface texture [3]. A problem that will

DETAIL OF AOTF AREA

gl JKlt .

AOTF

.FLUX

COLLECTOR

I \ -j RF IN

I—jock-in;

be faced in the analysis of TES data is the ubiquitous presence of soils

and rock coatings (e.g., [4]). It will be difficult to separate the portion

of the emission signal coming from weathering products from the

portion arising from emission of relatively fresh bedrock. An important use of COMPAS would be to clarify and confirm global

measurements by Mars Observer by characterizations at the rock

level of rock coatings and unweathered rock surfaces. This task can

only be accomplished at the rock scale. The results will address the

fundamental questions of what dominant rock types are exposed at

the surface and the nature of the surface-atmosphere interaction.

Measurement Approach: We plan to develop and demonstrate COMPAS, the Compositional Mineralogy P_hotoacoustic Spectrometer, for in situ spectral characterization of rocks and their

surface weathering products and/or the nature of adsorbed species.

Photoacoustic spectroscopy (PAS) is an established technique that

has been widely applied in spectral studies of complex, highly light

scattering, unprepared opaque samples. Existing PAS studies include rock and mineral characterizations and kinetic studies of the

same surface chemical reactions expected in photochemical weathering processes at the martian surface.

Microminiaturization of COMPAS to ensure compatibility with

simple microrovers is feasible. Our design goals for COMPAS are

volume< 125 cm3, weight< 110 g, and power consumption < 1.5 W.

The no-moving-parts COMPAS acquires single-point spectral data

serially at a modest data rate, compatible with microrover capabilities. COMPAS will measure spectra over at least 0.7-2.7 fim, the

prime spectral band for mineralogy and water detection for martian

environment surface studies. Subsequently we will define COMPAS

for extensions to both shorter and longer wavelengths. Since COMPAS

incorporates a thermal detector, the capability to sense an extremely

broad range of wavelengths is feasible so that rock types can be

measured at the wavelengths that yield optimum sensitivity or

minimum interference for the rock studied. COMPAS can acquire

spectra from the UV to the far-IR to study rocks, surface weathered

components, and adsorbed species. COMPAS can also profile surface layers to depths as great as 1 mm by using the variation of

absorption coefficients and the modulation frequency used in the

measurement. Then the depth profile of weathered samples can be

measured accurately to determine exposure ages.

PAS differs from conventional reflectance spectrometry in that it

uses the sample as the detector. Diffuse reflectance spectrometers

compare the reflectance of the sample with that of a standard so that

the difference between two quantities is measured. If the absorption

is large, little light is returned, or if small, only scattered light is

observed. In contrast, PAS senses only the effects on the sample of

the absorbed light and produces an "emissionlike" spectrum that is

entirely equivalent to the true absorption spectrum. The sample

responds to a modulated input flux by an expansion and contraction

that may be detected as an acoustic wave carried by the CO2

atmosphere of Mars. Since the pressure wave or the acoustic wave is

induced by the periodic temperature modulation in the rock induced

by the modulated absorption of incident light converted into heat,

scattered light has little effect on PAS.

COMPAS collects sunlight with a nontracked collector (either

aspheric or reflective) over ±3 hr from zenith and focuses it into a

fiber optic. The fiber optic transmits the flux to an acoustic-optic

tunable filter (AOTF) used to control and modulate the flux reaching

the sample. The AOTF output is collected by fiber optics and

illuminates the rock surface. The AOTF offers high transmission

Fig. 1.
LPl Technical Report 92-07, Part 1 17

(>75%), adaptable spectral resolution, an arbitrarily selectable spectral pass band, adaptable pass band shape, and high time resolution

as a shutter or light modulator, all under electronic control (see

[6.7]).

References: [1] Fegley B. G. and Treiman A. H. (1991) Proc.

Chapman Conference on Comparative Study of Venus and Mars.

preprint. [2] Surkov Y. A. et al. (1989) Nature, 342, 595. [3] Albee

A. L. and Palluconi D. F. (1990) Eos. 71. [4] Arvidson R. E. et al.

(19S9)JGR.94.1573-1587. [5] Smith W. H. (1990)S/>/£, 1318,25.

[6] Smith W. H. and Smith K. M. (1991) Exp. Ast., 1. 329.

1N94-2243 7

OPTICAL LUMINESCENCE SPECTROSCOPY ASA PROBE

OF THE SURFACE MINERALOGY OF MARS. A. H.

Treiman, NRC Associate, Code SN4, NASA Johnson Space

Center, Houston TX 77058, USA.

Executive Summary: Optical luminescence (OpL) spectroscopy is an attractive use of a visible-near-IR spectrometer on a Mars

lander because mineral products of atmosphere-surface interactions

on Mars will probably have characteristic OpL spectra. Optical

luminescence spectra would be taken at night, when a spectrometer

might otherwise sit idle. Also needed would be a source of exciting

radiation, which could be shared with other experiments.

Optical luminescence is emission of nonthermal optical photons

(near-UV through near-IR) as a response to energy input [1—3]. On

absorption of energy, an atom (or ion) will enter an excited state. The

favored decay of many such excited states involving valence-band

electrons is emission of an optical photon. Optical luminescence

spectra can be useful in determining mineralogy and mineral compositions.

Optical luminescence in crystals can arise from essential elements (or ions), trace-element substituents (activators), or defects.

Common activators in salts of alkali and alkaline earth elements

include Mn2+(VI), other transition metals, the rare earths, and the

actinides [3]. Trace substituents of other species can enhance or

quench OpL (e.g., Pb2+ vs. Fe3*). Optical luminescence can also arise

from defects in crystal structures, including those caused by radiation and shock.

Optical Luminescence on Mars: Atmosphere-surface interactions on Mars may yield many luminescent minerals, notably salts

of the alkali and alkaline earth elements [4-6]. Such phases are

products of martian weathering in the SNC meteorites [7-10], and

some do exhibit OpL. Scapolite has unusual OpL (Fig. 1), and any

scapolite on the Mars surface [11] should be readily apparent through

OpL spectrometry.

Luminescent minerals may be more common on Mars than Earth.

Martian surface materials are likely to have suffered significant

radiation damage from cosmic rays, which may create luminescent

defect structures. Some OpL mechanisms will be enhanced in the

cold of the martian night.

Optical Luminescence Excitation on Mars: To permit OpL

spectroscopy, a Mars lander must have an energy source for OpL

excitation, such as UV light, high-energy electrons, or heat.

Optical luminescence from U V light usually uses a Hg gas lamp,

an "off-the-shelf technology that would draw moderate power.

' However, Hg lamps may be fragile and are not very bright, thus

requiring that samples be brought to the spectrometer. Use of a U V

laser would resolve these problems and permit other laser-based

Scapolite

500 600 700 800 A,nm

Fig. 1. OpL spectrum of scapolite containing S2~. Scapolite formed in an

oxidizing environment will have a similar spectrum [2].

experiments (atmospheric OpL and scattering, distance ranging).

However, UV lasers commonly use gas or liquid media; solidmedium UV lasers are under development.

Optical luminescence excited by electron flux, cathodoluminescence (CL), is commonly used in geological sciences [12].

Cathodoluminescenceyields the brightest luminescence of available

methods, uses "off-the-shelf" technology, can work in ambient Mars

atmosphere (penetration to tens of centimeters), and produces characteristic X-rays (which may permit determination of chemical

compositions). However, CL would require a source of 10-15-kV

electrons, significant power resources, and transport of samples to

the spectrometer.

Optical luminescence emitted during heating, thermoluminescence (TL), is a standard technique in meteorite and radiation

studies. Thermoluminescence can be readily related to radiation

exposure, and a suitable heating chamber (like a TAPS calorimeter)

may be available on the lander. However, TL requires samples to be

within the lander, and does not utilize the wide range of activation

mechanisms tapped by CL and OpL methods.

Conclusion: Optical luminescence spectrometry could provide important and cost-effective constraints on the surface mineralogy. It could utilize a visible-NIR spectrometer during the times it

would otherwise be idle. The excitation source for OpL could be

shared with other science experiments, including atmosphere monitoring, calorimetry, or bulk chemical analyses.

Acknowledgments: I am grateful to L. P. Keller and J. DeHart

for stimulating discussions, and to J. L. Gooding for general support.

References: [1] Barnes D. F. (1958) Infrared Luminescence of

Minerals, U.S.G.S. Bull. 1052-C. [2] Marfunin A. S. (1975) Spectroscopy, LuminescenceandRadiationCenters inMinerals, Springer

Verlag, Berlin. [3] Waychunas G. A. (1988) In Spectroscopic

Methods inMineralogyandGeology(F.C.Haw\home.,ed.), 639-698,

Min. Soc. Amer., Washington, DC. [4] Gooding J. L. (1978)/cams,

33, 483-513. [5] Sidorov Yu. I. and Zolotov M. Yu. (1986) In

Chemistry and Physics of Terrestrial Planets (S. K. Saxena, ed.),

191-223, Advances in Physical Geochemistry, Vol. 6, Springer

Verlag, New York. [6] Fegley B. Jr. and Treiman A. H. (1992) In

Venus and Mars: Atmospheres, Ionospheres, and Solar Wind (J. G.

Luhmann et al., eds.), 7-71, AGU Geophys. Mon. 66. [7] Gooding

J. L. and Muenow D. W. (1986) GCA, 50, 1049-1059. [8] Gooding

J. L. et al. (1988) GCA. 52, 909-915. [9] Gooding J. L. et al. (1990)

Meteoritics. 25.281-289. [10] Gooding J. L. et al. (1991) Meteoritics, 26,135-143. [11] Clark R.N.etal.(1990)/G/?, 95,14463-14480.

[12] Marshall D. J. (1988) Cathodolwninescence of Geological

Materials, Unwin-Hyman, Boston.
18 Workshop on Chemical Weathering on Mars

MOSSBAUER SPECTROSCOPY ON MARS: WHAT TO

EXPECT. L. Vistiseni and J. M. Knudsen2, Wels Bohr Institute,

Blegdamsvej 17, DK-2100, Copenhagen 0, Denmark,

 2Physics

Laboratory, H.C. 0rsted Institute, Universitetsparken 5, DK-2100,

Copenhagen 0, Denmark.

Mossbauer spectroscopy is one of the most versatile tools for the

study of the physics and chemistry of iron compounds. Through this

simple technique information can be obtained on the oxidation state

of the iron and the distribution of the element on the various

accessible lattice sites in crystals. Mossbauer spectroscopy also

gives unique information on magnetic properties of compounds, be

they ferro-, ferri-, or antiferro-magnetic. In the study of superparamagnetism the technique is indispensable. The main objective of

the present paper is to show a few Mossbauer spectra of Mars sample

analogues and SNC meteorites. These spectra will suggest what

might be achieved by performing Mossbauer spectroscopy on the

surface of Mars.

Experimental: The spectra are recorded in backscatter geometry with no sample preparation, which is the method planned for

Mossbauer spectroscopy on Mars. The gamma rays are counted

using a silicon diode (Hamamatsu S3590-05), the

 S7Co source used

is about one year old, originally 100 mCi, and the drive is a

conventional one, not minimized. The collimator-source geometry

allows emission of gamma rays with a maximum deviation of 20°

from the central axis. The recording time for the spectra shown in Fig.

1 is 24 hr, except for spectrum cl, which was recorded over 7 days,

cl is aesthetically better than c2, but the information content is nearly

the same. It is expected that six detectors will be used in the

instrument sent to Mars, i.e., a recording time of 4 hr will in most

cases be sufficient. The results reported in this paper are obtained

with drive, detector, source, and sample at a temperature of —21°C.

Examples: Spectrum ashowsaclear distinction of threephases

present in a terrestrial basaltic rock: magnetite, ilmenite, and olivine.

The spectrum allows a quantitative determination of the distribution

of the iron in the three phases identified. It should be noted that even

with the described collimator-source geometry, it is possible to conclude that the magnetite contains impurities (in fact it is titanomagnetite). Spectrum b of a banded iron formation shows that

hematite, seen as "shoulders" on the outer lines, is clearly distinguished from magnetite.

Soil on Mars: The martian soil is colored red by Fe(ITI)

compounds, and during the Viking mission it was established that a

ferrimagnetic phase is present in the soil. The strongly oxidizing

compound in the soil, also found in the Viking mission, may be an

iron mineral. Part of the Fe(TII) on Mars is known to be present in

small particles (d < 10 nm), probably superparamagnetic. It is thus

an important problem in future missions to Mars to try to establish

the Fe(III) mineralogy in the surface fines.

As analogues to the martian dust we are studying terrestrial red

soils by Mossbauer spectroscopy. An example is spectrum c, which

shows the presence of hematite in a sample collected from a volcano.

The peaks in the middle of the spectrum show Fe(in), probably in

FeOOH. By magnetic separation a few percent of the sample can be

extracted, but this magnetic fraction is too small to be seen in the

spectrum.

Surface Rocks on Mars: The SNC meteorites are believed to

be rocks from Mars and may thus be used to anticipate what a

Mossbauer spectrum of the base rocks on Mars would look like.

hemaiiic

maenetiie

olivine

i iv. u

116.5

114. 0

lll.S

09. 0

06. S

04.0

01 -S

79 0

-12

37.0

32.2

2-7.5

22. 8

ie.0

13.2

os.s

03. e

- j

: fi

I1 1I

I1 1 1

J 1 J

- .

°TP.°f*.-yf^^

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- »Jfi ff^ r^f^fr1 ^

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_

fi

,"

; ij

i i

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i

V

 d

i

v

^S^. * fj, 4* ^^A^r

C *«.? " "«.D,0 ^.i.O^Jo.O 12.0

e

<

1

Fig. 1. Backscatlering Mossbauer spectra recorded at -21 °C of (a) a terrestrial

basalt (Smalands Taberg, Sweden), (b) a banded iron formation (Hamersley

Basin, Australia), (c) a red sample from a volcano (Samorin, Greece), cl 7 days

and c2 24 hours, (d) the SNC meteorite Nakhla, and (e) the SNC meteorite

Zagami.
LPI Technical Report 92-07, Pan 1 19

Spectra d and e of the SNC meteorites Nakhla and Zagami show the

presence of both pyroxene and olivine in Nakhla and only pyroxene

in Zagami. Possible Fe(HI) in these meteorites is below the detection

limit of the present set-up and so is the titanomagnetite known to be

present in these meteorites.

Conclusion: Through Mossbauer spectroscopy we might be

able to establish (1) the identity of the main iron-containing minerals

in the soil and rocks, including the determination of the fraction of

iron present in a given mineral; (2) the oxidation state of the iron in

the soil, i.e., the ratio Fe(n)/Fe(m); and (3) the nature of the magnetic phase in the soil, i.e., whether the phase is maghemite,

magnetite, or small-sized particles of hematite.

As shown above, small amounts of magnetic phases are difficult

to detect, and to fulfill the last task an adequate part of the iron must

be present in the magnetic phase.

DETERMINATION OF STABLE ISOTOPIC COMPOSITIONS OF H, C, N, O, AND S AT THE MARTIAN SURFACE

USING MASS SPECTROMETRY AND STEPPED COMBUSTION/PYROLYSIS. I. P. Wright1

, M. M. Grady2, and C. T.

Pillinger1, 'Department of Earth Sciences, Open University, Walton

Hall, Milton Keynes MK7 6AA, UK, ^Natural History Museum,

Cromwell Road, London SW7 5BD, UK.

The mechanisms by which the surface reservoirs of a planetary

body interact can be assessed through an understanding of the

distribution and stable isotopic compositions of the elements that

constitute the reservoirs. Of particular relevance to processes that

operate at planetary surfaces are the light elements: H, C, N, O, and

S. Conceptually, all these can be quantified and measured for

isotopic compositions using a single extraction system and mass

spectrometer. Rather than carrying out physical separations of the

components of interest, it is proposed that the elements under

investigation are selectively removed from appropriate samples

using the combined techniques of incremental pyrolysis and stepped

combustion.

The chemical and physical (and biological?) processes that act on

Mars will have left a record of their effects in the isotopic compositions of the different surface reservoirs (e.g., ices, fluids, gases,

magmatic components, secondary minerals, etc.). Isotopic analysis

of these, which will allow a reconstruction of the conditions prevailing at the time of formation, is obviously a demanding task for an

instrument that needs to operate remotely and autonomously at the

surface of theplanet. One potentially effective technique is to use the

different chemical and thermal properties of the individual constituents of interest to assist in the separation process. This can be effected

to some degree by treating a multicomponent sample to a process of

incremental heating (pyrolysis). A refinement of this is to perform

the experiment under 0.1 bar of pure oxygen (stepped combustion).

An exemplification of the value of this type of extraction can be given

for the case of sulfur, where iron sulfides combust to form SO2 at

temperatures below 600°C while sulfates decrepitate to give SO2 at

temperatures in excess of 600°C. Thus, without recourse to physical

separations it should be possible to make isotopic measurements of

sulfur in its different redox states.

Over the years we have extensively used stepped combustion

techniques and associated high-sensitivity mass spectrometers in the

laboratory for determining the distribution and isotopic compositions of elements such as carbon [1,2] and nitrogen [3,4]. The same

procedures can also be used for hydrogen and have been attempted

for sulfur [5]. All these techniques have been applied successfully to

studies of SNC meteorites [6,7]. A considerable advantage of

stepped combustion is that the elements of interest can still be

determined even if they exist in a refractory form. This technique has

even greater selectivity than simple pyrolysis and can be considered

as an adjunct to any heating system that would otherwise be on the

payload of a mission to Mars.

The deployment of stepped combustion for the analysis of surface

materials on Mars has the following requirements: (1) Availability

of a pumped, neutral mass spectrometer with a mass resolving power

of <100; such an instrument would also be utilized for atmospheric

analyses. (2) Provision of a robotic sampling device for collection

and delivery of materials from the vicinity of the landing site; such

a device would be common with other analytical experiments.

Specific to the stepped combustion experiment would be the reaction

vessel, which would need to be capable of temperature control in

steps over a range from ambient to a maximum of 1200°C. Temperatures less than this value would still be informative, but the chosen

maximum corresponds to that at which magmatic gases would be

liberated from minerals. In order to obtain isotopic measurements of

the highest precision it would be desirable to incorporate as part of

the analytical instrumentation a facility to meter out small quantities

of reference gas to enable in situ calibration of the mass spectrometer.

Much of the procedural protocol for stepped combustion has

already been evaluated in the laboratory. For example, solid reagents

that can supply oxygen in the gas phase at temperatures as low as

200°C are known; excess oxygen can either be vented from the

system or chemically resorbed for further usage. A number of

purification schemes have been advanced to allow selective admittance of a single gaseous species to the mass spectrometer (thereby

avoiding isobaric interferences). In the laboratory experiments, only

one gas is ever analyzed in an individual mass spectrometer. Since

the instrument destined for Mars would need to be highly efficient,

it would be necessary not only to purify the gases of in terest (H2, CO2,

N2, and SO^ but also to separate them for the purposes of sequential

isotopic measurement This could be readily achieved provided

cryogenic cooling is available. An alternative would involve the use

of chromatographic separation or even some form of solid-phase

chemical reactions.

The concept of active chemical analysis could be adapted further

for measuring the oxygen isotopic compositions of martian minerals

provided that a source of fluorine can be transported to Mars. A

convenient way of doing this would be to use solid K2NiF6.KF, which

decomposes to give fluorine gas at 400°C. By reacting the fluorine

with silicates, etc., it would be possible to liberate O2 gas for analysis.

In this way it would be possible to measure both

 16O/18O and 16O/17O

ratios.

References: [1] Prosser S. J. et al. (1990) Chem. Geol., 83,

71-88. [2] Yates P. D. et al. (1992) Chem. Geol., 101, 81-91.

[3] Wright I. P. et al. (1988) J. Phys. E: Sci. Instrum., 21, 865-875.

[4] Boyd S. R. et al. (1988) J. Phys. E: Sci. Instrum., 21, 876-885.

[5] Burgess R. et al. (1991) Meteoritics. 26, 55-64. [6] Burgess R.

et al. (1989) EPSL. 93, 314-320. [7] Wrightl. P. et al. (1992) GCA,

5<5,817-S26.