Smithsonian

Contributions to Astrophysics

VOLUME 5, NUMBER 14

THE SPACE DENSITY OF ATMOSPHERIC DUST IN THE

ALTITUDE RANGE 50,000 TO 90,000 FEET

by PAUL W. HODGE AND FRANCES W. WRIGHT

SMITHSONIAN INSTITUTION

Washington, D.C.

1962
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The Space Density of Atmospheric Dust in the

Altitude Range 50,000 to 90,000 Feet'

By Paul W. Hodge2 and Frances W. Wright3

The importance of collecting and analyzing

meteoritic dust particles has been enhanced by

the recent suggestion of a remarkably localized

dust cloud about the earth (Whipple, 1961a),

and by the likelihood that this dust has a

lunar origin (Whipple, 1961b). Artificial satellites efficiently provide the evidence for the

probable existence of the earth's dust belt;

however, they are not yet capable of capturing

samples of this material and returning them

to earth for analysis. For such highly desirable

samples we must at present rely on the earth's

atmosphere to act as a cushion, braking the

high-velocity particles and concentrating them

in sufficient numbers for collection on highflying aircraft and balloons.

The Smithsonian Astrophysical Observatory

has been employing jet aircraft and balloons to

collect particles from various levels of the

stratosphere. In previous publications we have

described a series of particle collections made

at altitudes of 30,000 to 50,000 feet (Hodge

and Rinehart, 1958; Hodge, 1961; Wright,

Hodge, and Fireman, 1961). Fireman and Kistner (1961) and Riggs, Wright, and Hodge (1962)

have made chemical analyses of some of these

particles. The present paper presents results

1

 This work was supported in part by Contract AF 19(604)-6627 with

the Qeophysical Research Directorate, Air Force Cambridge Research

Center, Cambridge, Mass. We wish to acknowledge the excellent

assistance of the Flight Research Center of the National Aeronautics

and Space Administration, Edwards, California, and of Mr. Terry

Larson of the National Aeronautics and Space Administration.

1

 Smithsonian Astrophysical Observatory and Berkeley Astronomical

Department, University of California.

* Smithsonian Astrophysical Observatory and Harvard College Observatory, Cambridge, Mass.

of the first of a series of collections at altitudes

between 50,000 and 90,000 feet, made in

cooperation with the Flight Research Center

of the National Aeronautics and Space Administration.

Collecting procedure

The collector.—The device used in the present

collecting program is a refinement of our

first collector, which was flown on a U-2 (see

photograph in the paper by Rados, 1960, that

describes our U-2 program). It is nearly

identical with the device flown on the B-52

(Hodge, 1961), although mounted on the aircraft differently. Air is admitted to an expansion chamber and filtered by a Millipore

filter, which retains all particles down to the

submicron range. The shutter mechanism and

filter housing are so designed that exposure of

the filter to air at times other than the period

during which the shutter is open in flight is

minimized.

Location on aircraft.—The collector was flown

on an F-104A aircraft by the Flight Research

Center of the National Aeronautics and Space

Administration, out of Edwards, Calif. Plate 1

shows the device in place on the tip of the right

wing of the aircraft; an identical collector was

also mounted on the left wing, but it was not in

operation. The wing tip was chosen as a prime

location because contamination of the sample by

the body of the craft was minimized.

Flight characteristics.—A pressure switch installed on the wing activated the shutter at an

altitude of about 55,000 feet, so that dust was

collected continuously at all heights above this

limit. The flights of the F-104A on which

231

644484—62
232 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS VOL. B

collections were made were typically shortduration, high-altitude climbs to above 80,000

feet. Collections were made on nine such

flights. Heights, velocities, temperatures and

wind characteristics for each flight are shown

in table 5.

Examination of samples

Microscope procedure.—We made a general

survey of each filter (40 mm in diameter) from

edge to edge, with a microscope of 200 X magnification, and measured, described, and recorded

the position of all types of particles larger than

6/* (mean diameter).

Then, within the central exposed portion of

the filter (a circle of 14-mm diameter), we made

a survey under 400 X magnification, and measured, described, and recorded the positions of

all opaque particles with mean diameters larger

than 3/x. The numerical results of these two

scannings are shown in table 1.

Classification of particles.—We found that all

particles examined were included in the following classification scheme:

1. Black, shiny metallic particles; they may be rough or

smooth. Designation, M.

2. Black, non-shiny particles. Designation, B.

3. Dark brown and dark gray particles. Designation,

Z>.

4. Gray, stone-colored chunks. Designation, Gy.

5. Colored particles, usually with smooth outlines; most

of these seem to be semitransparent. Designation,

C.

6. Transparent, clear particles. Designation, T.

7. Aluminum chips, from the walls of the collector.

Designation, Al.

8. Green-black ovals. Designation, Gn-B.

9. Metallic particles similar in appearance to iron filings.

Designation, M(C).

The second scan, within the 14-mm circle,

excluded the very numerous colored and transparent particles.

The complete scanning data are given in

table 4.

Results

Description of flights and collections.—The

characteristics of the nine flights were all very

nearly the same. Exposure times averaged

95 seconds, with a dispersion of about 20

percent; maximum altitudes averaged 83,000

feet with a dispersion of only 9 percent. The

small differences in the exposure times or altitudes of different flights are not expected to

affect greatly the number or nature of particles.

For this reason the observed numbers of particles are expected to reflect primarily differences in space density rather than in flight

characteristics.

Table 1 summarizes the individual flight

characteristics and scanning results, details of

which are given more completely in table 5.

Table 1 shows the total numbers of particles

(with mean dimensions greater than 3M) on the

exposed portions of each filter; this value was

computed from counts on smaller areas, and

over a different size range, by applying the

appropriate multiplication factors (e.g., the

known size distribution). The numbers of

opaque particles given in table 1 are those

directly observed and measured.

TABLE 1.—Flight characteristics and number of nonaluminum particles

Filter

no.

G8

G16

Nl

N2

N3

N4

N5

N7

N9

Exposure

(sees)

103

77

92

94

87

96

100

102

103

Alt. range

(1000 ft)

51 to 85

52 to 82

51 to 83

53 to 85

56 to 78

52 to 83

52 to 78

52 to 85

52 to 87

Total no.

particles

(mean diameter

>3M)

80

560

2080

160

40

80

80

5200

120

No. opaque

particles

(mean diameter

>3M)

43

69

359

81

15

40

18

510

63

From the data of table 1 three facts are

evident. (1) The total number of particles and

the number of opaque particles vary widely,

over a range of two orders of magnitude. (2)

The two values agree in their differences; when

the number of all types of particles is high, the

number of opaque particles is high. (3) The

ratio of total to opaque varies between 2 and 10,

and is larger when the actual values are larger.

Computed space densities.—Because the collector's altitude and velocity varied widely

during the collections, we cannot obtain

straightforward space densities as a function of

height. Instead, we obtain a mean value,

weighted according to altitude by the volume

encountered as a function of altitude. This

space density is computed by
HODGE AND WRIGHT PLATE 1

SPACE DENSITY OF ATMOSPHERIC DUST 233

where p is the weighted mean density, k is the

efficiency of the collector, NQ is the number of

collected particles (total minus contamination),

and V is the volume encountered by the collector (kV is the volume swept out).

In our case, iV0 is taken as equal to the value

given in table 1 if we assume no contamination

(thus giving an upper limit to p). The volume

encountered is taken to be

TABLE 2.—Particles per cubic meter (mean diameter >3M).

V=A V\(t)dt,

where A is the area of the opening of the collector (3X10-6m

2

); v(t) is the aircraft's velocity

as a function of time; and tx is the time of the

beginning, and t2 the time of the end of the

exposure.

We do not have direct values for v(t), but

we do know M(t), the Mach number as a function of time. This value is related to the

velocity of the plane with respect to the air by

v(t)=20.lM(t)JT(t),

where M(/) is the Mach number and T(t) is the

temperature in absolute units.

Thus we can compute the average space

density of particles by the equation

6X10" 'M(t)

particles/m3

This has been done numerically for the flights,

and results are given in table 2. The volume

of air sampled in each case is nearly one cubic

meter, and the value for kp~ is normally of the

order of 150 particles per cubic meter for all

particles with diameters greater than 3;u- The

average value is 156, excluding Nl and N7

(see below).

The efficiency k of the collector has been determined from wind-tunnel tests carried out by

P. Stroom of General Mills. He made an experimental calibration by injecting particles

into the air stream, and then comparing the

number collected by our device and that collected by a collector of known efficiency. The

calibration showed that at Mach 0.6 and altitude 50,000 feet our collector is 15 percent

Filter no.

G8

G16

Nl

N2

N3

N4

N5

N7

N9

kp

80

480

2290

192

38

82

85

5720

132

efficient. This low efficiency results from the

very small pore-size of the filters and from some

loss on the walls and other portions of the collector. The central part of the collector retained 7 percent of the particles; the remainder

were concentrated near the edges. Calculations based on pressure differentials measured

in the wind tunnel indicate that the efficiency

of filtering increases with velocity and decreases

with height. For a typical F-104A flight this

efficiency varies between 0.7 and 4.1 times that

of the nights at 50,000 feet and Mach 0.6.

Experimental tests with particles were not

carried out for Mach numbers greater than 0.6,

so that we estimate the efficiency from the

pressure data. We believe that a realistic time

average for the F-104A flights is an efficiency

of approximately 15 percent ±3 . We adopt a

value of 0.15 for k; the derived space density p

is nearly 7 times the values of kp tabulated in

table 2. Thus the space density is normally of

the order of 1000 particles larger than 3/x per

cubic meter.

0.0

70

H (1000 ft.)

FIGURE l.—The volume of air, F, encountered by the collector

between heights H and H-f 5,000 feet, expressed as a

function of altitude.
234 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

In figure 1, the volume of air encountered is

shown as a function of altitude for the typical

flight on which filter G8 was flown. The diagram indicates that the volume of air is not a

rapidly varying function of altitude, and that,

within the accuracy to which we can discuss the

present data, the computed p is very nearly

equivalent to a mean space density for altitudes

between 55,000 and 85,000 feet.

On two filters, Nl and N7, the calculated

values of k~p are much greater than the average.

This seems to be the result not of contamination, but of the encounter of the aircraft with a

dust-enriched portion of air. We have found

that accidentally contaminated samples, such

as N6 and N8 (see table 4), contain large

amounts of aluminum particles, while the

amount of aluminum dust on filters Nl and N7

was equal to the normal background count.

In each case, and especially for filter Nl, there

is a large cluster of particles, nearly centered on

the filter, where most of the dust is located

(fig. 2). The remainder of the filter has the

density of particles typical of the other filters.

Thus the unusually high count is due exclusively to the compact cluster, which appears

to consist of fragments of a larger, conglomerate

particle that may have disintegrated on contact

with the filter or while entering the collector.

Such a particle must have been relatively

fragile and of low density, with a diameter of

the order of 100/z and mass of the order of

10~7 gm. It is tempting to enquire whether

such a particle can be extraterrestrial in origin.

Meteor studies suggest that meteoroids are

primarily low-density, fragile bodies derived

from comets. Fragments of such bodies might

well have the appearance of the object we

collected. It is of great importance to check

such a possibility by means of more collections.

TABLE 3.—The size distribution of particles with mean

diameters larger than 3M; the limiting mean diameter

of opaque particles collected on these filters was 21ft.

TABLE 4.—Complete scanning data

Mean diameter

(microns)

3.0 to 5.9

6.0 to 8.9

9.0 to 11.9

12.0 to 14.9

15.0 to 17.9

18.0 to 20.9

Percent of

total sample

67.3

26.2

4.8

1.2

0.4

0.1

Filter

No.

G8

G16

Nl

N2

N3

N4

N5

N6*

N7

N8*

N9

No. particles

of all types

in 14 mm2

with mean

diam. >6M

1

7

26

2

0.5

1

1

131.2

65

5

1.5

No. particles in 140

mean diameter

Total:

all but

CandT

43

69

359

81

15

40

18

441

510

260

63

B

and

M

34

40

309

38

12

24

6

86

227

32

28

Gy

3

12

87

5

1

1

1

36

39

35

3

mm2

> 3 M

M(O

0

4

1

0

0

0

0

133

6

151

2

with

Al

27

143

99

75

16

16

16

1592

122

947

2

• Unexposed and heavily contaminated; flown on left wing, new

collector.

From our limited data, assuming k=l for this

encounter, we calculate tentative space densities of 0.1 such particle per cubic meter.

This corresponds to a rate of fall on the earth

of about 104 tons/day, using the method of

estimating the mass rate of fall described by

Fireman and Kistner (1961).

Conclusions

From microscopic studies of particles collected

in the upper atmosphere, we find that at altitudes of 50,000 to 90,000 feet there are per

cubic meter approximately 1000 particles larger

than 3M in diameter. This is approximately

one-fourth of the value derived by identical

methods at altitudes of 40,000 to 50,000 feet.

The space density may fluctuate widely. A

maximum of roughly 30 percent of these are

opaque particles, so that the upper limit for the

space density of meteoritic dust in the atmosphere must be approximately 300 particles

larger than 3n per cubic meter. Using the

assumptions of Fireman and Kistner (1961), we

calculate an upper limit to the influx rate of

meteoritic material of roughly 104 tons/day.

The tentatively identified meteoric particles

give a lower limit of 104 tons/day for their influx

rate.

We plan to make further collections with a

more refined collecting device. These will

attempt to determine (1) the nature and number of the large fragile particles, such as those
SPACE DENSITY OF ATMOSPHERIC DUST 235

S

 "

X •

2 m m

FIGURE 2.—The distribution of 359 opaque particles on filter Nl, showing the dump of particles believed to have resulted from the

disintegration of a larger fragile particle on impact or while entering the collector.
236 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

on filter Nl; (2) the distribution with height of

the opaque particles to test the present indication of a lack of decrease with height; and (3)

the chemical composition of those particles

that from their distribution with height appear

to be extraterrestrial.

TABLE 5.—Flight data far filters

Explanation of column heads: (2), time after take-off; (3), Mach number

for plane's velocity; (4), the dynamic pressure of the air on the aircraft,

measured in pounds per square foot. The figures in columns (5), (6), and

(7) were obtained by a meteorological balloon on the day of the plane

flight.]

FILTER G8

Date of flight, June 21, I960. Altitude range at which filter was exposed,

51,600 to 85,400 feet. Mach number range during the exposure of the

fllter,0.65tol.70. Airplane beading, from magnetic north, 0.65°. Takeofl time, 0815 P.S.T. Length of time filter was exposed, 102.7 seconds.

General atmospheric conditions, clear, ground haze. Time of temperature and wind data, 0810 P.S.T.

(1) (2) (3) (4) (5) (6) (7)

Altitude

(ft.)

50,000

55,000

60,000

65,000

70,000

75,000

80,000

85,000

85,000

80,000

75,000

70,000

65,000

60.000

55,000

50,000

Time

(sec.)

75.5

79.8

84.0

88.7

93.3

98.8

107.8

122.5

130.0

146.0

154.0

159.5

164.5

169.7

174.5

179.5

Mach

no.

1.75

1.66

1.54

1.40

1.25

1.08

0.89

0.66

0.66

0.90

1.10

1.20

1.30

1.40

1.46

1.44

q

(p.s.f.)

515

370

250

145

100

60

30

15

12

35

60

95

140

205

285

355

Fn/TEB O1S

Temp.

(C)

-68.3°

-65. 9

-63. 1

-66. 7

-54. 0

-52. 6

—49.3

-45. 8

Wind

speed

(knots)

35

14

03

12

18

21

30

31

Wind

direction

260°

265

040

099

104

100

080

090

Date of flight, July 15,1960. Altitude range, 51,600 to 82,000 feet. Mach

no. range, 0.75 to 1.58. Airplane heading, from magnetic north, 065°.

Take-off time, 0940 P.S.T. Length of time filter was exposed, 76.7

seconds. Oenerel atmospheric conditions, clear. Time of temperature

and wind data, 0820 P.S.T.

(U (2) (3) (4) (5) (8) (7)

FILTER N l

Date of flight, August 2, 1960. Altitude range, 51,000 to 83,200 feet.

Mach no. range, 0.44 to 1.65. Airplane heading, from magnetic north,

245°. Take-off time, 0949 P.S.T. Length of time filter was exposed,

91.7 seconds. General atmospheric conditions, clear. Time of temperature and wind data, 0820 P.S.T.

(1) (2) (3) (4) (5) (6) (7)

50,000

55,000

60,000

65,000

70,000

75,000

80,000

85,000

80,000

75,000

70,000

65,000

60,000

55,000

50,000

21.5

25.6

29.7

33.8

38.1

43.6

52.6

—

86.5

97.2

102.7

107.1

111.

114.8

118.2

1.80

1.66

1.51

1.37

1.21

1.07

0.90

—

0.67

1.00

1.17

1.30

1.40

1.49

1.57

550

365

240

155

92

61

32

—

18

50

90

—

205

295

410

-65.8°

-65. 4

-60. 8

-58. 4

-53. 2

-51. 9

-48. 3

-47. 8

18

16

12

16

19

29

24

27

203°

150

130

105

106

098

124

092

FILTER N2

Date of flight, August 9, 1960. Altitude range, 52,700 to 85,400 feet.

Mach no. range, 0.57 to 1.69. Airplane heading, from magnetic north,

265°. Take-off time, 0958 P.S.T. Length of time filter was exposed,

94 seconds. General atmospheric conditions, clear. Time of temperature and wind data, 0925 P.S.T.

(1) (2) (3) (4) (5) (6) (7)

50,000

65,000

60,000

65,000

70,000

75,000

80,000

85,000

85,000

80,000

75,000

70,000

65,000

60,000

55,000

60,000

30.4

35.0

39.2

43.6

48.7

55.7

61.8

76.0

86.5

100.5

107.2

113.0

120.4

123.0

127.1

131.0

1.83

1.69

1.51

1.36

1.16

0.95

0.83

0.59

0.59

0.82

0.99

1.13

1.35

1.42

1.51

1.56

550

370

235

160

95

46

28

11

11

28

50

84

190

220

300

400

FILTER N3

-68.4°

-68. 6

-63. 5

-67. 3

-54. 5

-51. 8

-47. 7

-45. 6

16

9

7

15

25

25

23

24

300'

114

062

096

090

097

090

094

Date of flight, August 12, 1960. Altitude range, 55,500 to 78,000 feet.

Mach no. range, 1.19 to 1.73. Airplane heading, from magnetic north,

246°. Take-off time, 1200 P.S.T. Length of time filter was exposed, 87

seconds. General atmospheric conditions, clear. Time of temperature

and wind data, 0730 P.S.T.

(1) (2) (3) (4) (5) (6) (7)

50.000

55.000

60.000

65.000

70,000

75,000

80.000

85.000

80.000

75,000

70,000

65,000

60.000

55,000

50.0P0

26.0

30.0

34.7

39.5

45. 3

51.2

61.0

—

82.0

93.5

101.0

106.8

112.2

117.0

121.8

1.71

1.61

1.46

1.30

1.14

1.00

0. SI

—

0. S7

1.10

1.26

1.36

1.45

1.48

1.47

—

—

—

146

86

53

28

—

26

50

87

132

—

—

—

-67 . 7°

-66. 4

-64. 7

-58. 8

-56. 3

-53. 7

—50. 1

-46. 1

16

15

13

17

22

29

33

26

245°

188

156

108

72

84

90

90

50,000

55,000

60,000

65,000

70,000

75,000

80,000

85,000

80,000

75,000

70,000

65,000

60,000

55,000

60,000

235.4

241.2

247.0

253.7

262.3

273.0

_

_

301.4

310.3

318.2

325.5

331.3

336.3

1.80

1.74

1.65

1.53

1.38

1.25

_

1.25

1.35

1.46

1.57

1.65

1.69

555

420

285

190

115

75

80

120

175

265

385

480

-69.9°

-70. 8

-63. 5

-58. 8

-56. 7

-49. 6

-50. 7

-46. 5

03

12

15

12

20

23

24

21

231

106

088

080

070

083

100

094
SPACE DENSITY OF ATMOSPHERIC DUST 237

TABLE 5.—Flight data for filters—Continued

FILTER N4

Date of flight, August 25, 1960. Altitude range, 51,600 to 82,700 feet.

Macb no. range, 0.66 to 1.74. Airplane heading, from magnetic north,

245°. Take-ofl time, 1150 P.S.T. Length of time filter was exposed,

96 seconds. General atmospheric conditions, clear. Time of temperature and wind data, 0935 P.S.T. Airplane missed runway on landing;

possible contamination by dust from crash trucks.

(1) (2) (3) (4) (5) (6) (7)

50,000

55,000

60,000

65,000

70,000

75,000

80,000

85,000

80,000

75,000

70,000

65,000

60,000

55,000

50,000

36.4

41.4

46.6

62.0

58.7

66.0

72.0

—

99.3

104.6

112.7

119.3

124.7

130.2

135.0

1.78

1.64

1.43

1.25

1.07

0.91

0.80

—

0.77

0.86

1.05

1.23

1.35

1.49

1.57

530

350

215

125

75

40

30

—

30

40

70

125

190

295

430

FILTER N5

-67.3°

-67.0

-60.6

-57.9

-53.2

-51.2

-48.9

-45.0

30

18

06

07

12

21

25

24

250°

257

190

143

120

100

100

090

Date of flight, August 31, 1960. Altitude range, 51,600 to 78,200 feet.

Mach no. range, 0.66 to 1.75. Airplane beading, from magnetic north,

245°. Take-off time, 1015 P.S.T. Length of time filter was exposed,

99.5 seconds. General atmospheric conditions, clear. Time of temperature and wind data, 0835 P.8.T. Dusty landing.

(1) (2) (3) (4) (5) (6) (7)

50,000

55,000

60,000

65,000

70,000

75,000

80,000

85,000

80,000

75,000

70,000

65,000

60,000

55,000

50,000

34.5

40.0

45.6

51.5

58.6

68.5

—

—

—

104.5

113.5

120.4

126.3

131.7

136.8

1.80

1.63

1.45

1.28

1.07

0.82

—

—

—

0.88

1.07

1.22

1.32

—

—

550

380

205

140

75

35

—

—

—

40

80

125

185

—

—

-61.8°

-64.9

-61.2

-54. 9

-54.9

-53.0

-50.2

-47.3

28

14

12

12

15

18

19

24

197

185

171

118

090

100

086

090

FlLTEB N7

Date of flight, October 4, 1960. Altitude range, 52,000 to 85,200 feet.

Mach no. range, 0.65 to 1.73. Airplane heading, from magnetic north,

245°. Take-off time, 0935 P.S.T. Length of time filter was exposed,

101.5 seconds. General atmospheric conditions, very clear, calm. Time

of temperature and wind data, 1000 P.S.T.

(1) (2) (3) (4) (5) (6) (7)

50,000

55,000

60,000

65,000

70,000

75,000

80,000

85,000

85,000

80,000

75,000

70,000

65,000

60,000

55,000

50,000

35.0

39.7

40.5

49.6

54.8

59.9

08.3

84.0

91.0

108.0

115.5

122.0

127.0

132.5

137.5

143.0

1.85

1.71

1.69

1.39

1.23

1.11

0.87

0.66

0.65

0.88

1.06

1.22

1.31

1.41

1.46

1.46

575

390

370

360

100

60

30

12

12

28

60

95

135

210

280

360

-60.3°

-62.2

-60. 2

-57.7

24

14

07

04

2.WO

230

224

229

Data not acquired for higher

altitudes.

FlLTEB N 9

Date of flight, October 4, 1960. Altitude range, 52,500 to 86,600 feet.

Mach no. range, 0.76 to 1.80. Airplane beading from magnetic north,

245°. Take-off time, 1345 P.S.T. Length of time filter was exposed,

102.6 seconds. General atmospheric conditions, clear, wind at 10 knots.

Time of temperature and wind data, 1000 F.S.T.

(1)

50,000

65,000

60,000

65,000

70,000

75,000

80,000

85,000

85,000

80,000

75,000

70,000

65,000

60,000

55,000

50.000

(2)

33.5

38.7

43.3

48.3

53.2

59.8

66.8

77.8

97.8

108.4

116.3

122.0

127.4

132.3

137.2

142.5

(3)

1.90

1.76

1.65

1.47

1.32

1.14

0.99

0.81

0.81

0.99

1.14

1.27

1.37

1.45

1.52

1.57

(4)

625

420

285

175

115

60

40

20

20

40

70

105

155

215

305

410

(5)

-60.3°

-62. 2

-60. 2

-57.7

(6)

24

14

07

04

(7)

250°

230

224

229

Data not acquired for higher

altitudes

References

FIREMAN, E. L., AND KISTNEK, G.

1961. The nature of dust collected at high altitudes. Geochim. et Cosmochim. Acta,

vol. 24, pp. 10-22.

HODGE, P. W.

1961. Sampling dust from the stratosphere.

Smithsonian Contr. Astrophys., vol. 5,

No. 10, pp. 145-152.

HODGE, P. W., AND RlNEHART, J. S.

1958. High-altitude collection of extraterrestrial

particulate matter Paper presented at

100th meeting of the American Astronomical Society, Madison, Wis., June 29-

July 2. (Abstract published in Astron.

Journ., vol. 63, p. 306).

RADOS, R. M.

1960. The U-2 as an instrumented aircraft for

geophysical research. Weatherwise, vol.

13, p. 232 ff.

RIGGS, F. G., JR.; WRIGHT, F. W.; AND HODGE, P. W.

1962. Chemical analysis of 643 particles collected

by high-altitude aircraft and balloons.

Smithsonian Astrophys. Obs., Special

Report No. 99, 41 pp.

WHIPPLE, F. L.

1961a. The particulate contents of space. In

P. Campbell, ed., Medical and biological

aspects of the energies of space, pp. 49-

70. Columbia University Press, New

York.

1961b. The dust cloud about the earth. Nature,

vol. 189, pp. 127-128.

WRIGHT, F. W.; HODGE, P. W.; AND FIREMAN, E. L.

1961. A search for micrometeorites in the earth's

atmosphere. Paper presented at 108th

meeting of the American Astronomical

Society, Nantucket, Mass., June 18-21.

(Abstract published in Astron. Journ.,

vol. 66, pp. 298-299).
2 3 8 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS VOL. B

Abstract

Collections of participate matter have been made in the altitude range from 50,000 to 90,000 feet by means of

high-altitude, short-duration flights of an F-104A jet aircraft of the NASA Flight Research Center. The average

space density of particles larger than 3/x in diameter is estimated to be 1000 particles per cubic meter at these altitudes.

The derived space density varies considerably, as previously found for altitudes in the range from 40,000 to 50,000

feet. Only a small percentage of these particles are possibly meteoritic.