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Zinc, lead, chlorine and FeOOH-bearing assemblages in the Apollo 16 sample 66095: Origin by impact of a comet or a carbonaceous chondrite?
EARTH AND PLANETARY SCIENCE LETTERS 18 (1973) 411-419. NORTH-HOLLAND PUBLISHING COMPANY
[]
ZINC, LEAD, CHLORINE
AND FeOOH-BEARING
ASSEMBLAGES
IN THE APOLLO
16
SAMPLE 66095: ORIGIN BY IMPACT OF A COMET OR A CARBONACEOUS
CHONDRITE?
A. E1 GORESY, P. RAMDOHR, M. PAVI~E W I~ :~ , O. MEDENBACH, O. MOLLER and W. GENTNER Max.Planck.lnstitut ffir Kernphysik, HeMelberg, Germany Received 2 February 1973 Revised version received 19 February 1973 Sample 66095,89 collected from station 6 from the lunar Highlands in the Descartes Site shows evidence of mild to severe shock. These shock features are accompanied by an unusual enrichment in the volatile elements C1, Zn and Pb and by the presence of FeOOH. FeOOH occurs in two distinct assemblages: (l) with metallic FeNi, (2) with troilite, sphalerite and two CI bearing Zn, Fe sulfates. Lead is present exclusively in the second assemblage at the boundaries between troilite and goethite. Lead concentrations up to 0.4% were found. However, the nature of lead-bearing phase is unknown. X-ray fluorescence analyses of a 10 X 6 mm area of the thin section also yielded enhanced chlorine, sulfur and zinc contents. The formation of this unique assemblage and the introduction of the material rich in volatile elements is very probably genetically connected with an impact of a carbonaceous chondrite or a comet. The small range of the reaction between the volatile rich gases and metallic FeNi and troilite indicate a short-live-phenomenon and thus fumarolic activity is a very unlikely process.
1. Introduction Study o f lunar samples recovered during Apollo and Luna missions demonstrated that the lunar rocks are depleted in water, volatile compounds and that trivalent iron is absent in many lunar minerals. Of the rocks collected during tile Apollo 16 mission one sample, 66095 collected from station 6 near South Ray Crater proved to be unique among the recovered Apollo 16 rocks. Rusty areas consisting of goethite were observed to occur around original components [1]. I f goethite is formed on the lunar surface then we have to consider the possibility o f water release from deeper regions o f the moon or goethite formation by oxidation of preexisting minerals due to an impact of a water bearing body presumably a carbonaceous chondrite or a comet. Whipple's * Present address: Institut Za Bakar, Bor, Yugoslavia.
theory [2] that comets are fundamentally balls o f ice and dirt is now widely accepted. In this report we are presenting mineralogical and chemical evidence that FeOOH in sample 66095,89 is formed on the lunar surface probably by impact of an object rich in the volatile elements Zn, Pb, C1, and water. The present investigations did not establish the nature of FeOOH compound present in this sample if it is goethite, akaganeite or lepidocrocite. In this paper we are going to call this compound for simplicity goethite until its nature is clarified. Sample 66095,89 allocated to us is a high grade metamorphic breccia o f type III according to the petrographic classification o f the PET-report [1]. The sample is heavily shocked and is penetrated by several veins filled with shock melted silicate glass containing thousands o f metallic spherules. The opaque minerals observed in the plagioclase rich groundmass are: metallic FeNi, troilite, schreibersite, cohenite sphalerite, ilmenite, baddeleyite, goethite, different Zn, C1 and S bearing
412
A. El Goresy et aL, Zn, Pb, CI and FeOOH-bearing assemblages in the Apollo 16 Sample 66095
phases and a Pb rich phase. Goethite occurs in two distinct exotic assemblages one with metallic FeNi and the other with troilite and sphalerite.
2. Results and discussion
2.1. FeNi metal and schreibersite
Metallic FeNi occurs as large blebs up to 1 mm in size sporadically distributed in the silicate matrix and as metallic spherules in the shock produced silicate glass veins. Both metal blebs and spherules are optically and chemically one metallic phase of kamacite composition. Electron microprobe analyses of numerous grains indicate narrow compositional variation. Furthermore, no difference in chemistry was found to exist between metal blebs in the silicate groundmass and spherules in the glass veins. These findings indicate that the spherules are formed by shock melting of preexisting metal blebs. Both metals have an average composition o f 94.3% Fe, 5.51% Ni, 0.37% Co, and 0.14% P. Fig. 1 shows the Ni content versus Co content o f all grains analyzed. Using the criteria set forward by Goldstein et al. [3, 4] the present findings indicate that the FeNi metals in sample 66095,89 fall within the meteoritic composition. In composition and structure they are also J
2.8 ~ J 2.~
66095,89
2.0 1.6
~ J
2 12.
J
5
similar to phosphide-metal particles described by Goldstein et al. [3] from the Apollo 12 landing site. The metals encountered in this sample are very probably meteoritic debris incorporated in the breccia long before solidification and metamorphism. However, the very narrow composition of the metals is striking. Several metal grains were found to contain schreibersite inclusions (fig. 2). As shown in this figure the schreibersite occurs as blebs or small idiomorphic crystals. Numerous schreibersite grains were analyzed and some selected data are shown in table 1. No apparent compositional variation from grain to grain was observed. The Co-content is quite low compared to that of coexisting kamacite.
J
Table 1 Selected electron microprobe analyses of schreibersites from sample no. 66095,89
8"
0
Fig. 2. A metal particle with schreibersite inclusion (light grey). The metal grained is rimmed by troilite (dark grey). Reflected light.
10
15 20 wt % Ni Fig. 1. Co versus Ni content of metal blebs in the metamorphosed breccia groundmass and metallic spherules in shock melted silicate glass veins. The lower two curves define the composition range of meteoritic metal. The box on the left side defines the low Ni and low Co metals of the Apollo 11 basalts. The upper two curves define the composition of the Apollo 12 metals. The outlines of this diagram are after Goldstein and Axon [4].
1
2
3
4
Fe
66.7
68.5
67.7
68.8
P
14.8
15.0
14.8
14.9
Ni
17.1
15.1
15.9
14.4
Co Total
0.09
0.12
0.08
0.15
98.69
98.72
98.48
98.52
A. El Goresy et aL, Zn, Pb, Cl and FeOOH-bearingassemblages in the Apollo 16 Sample 66095
Fig. 3. Metal blebs cut by several shock melted silicate veins. Photomicrograph shows metallic spherules to be formed by shock melting of preexisting metal. Reflected light. 2.2. Exotic assemblages Two exotic assemblages in which goethite occurs were observed in sample 66095,89: (1) Goethite or at least a goethite rich mixture as reaction rims around metal blebs. The metallic spherules in the shock melted silicate glass veins do not show such goethite reactions (fig. 3). The metal blebs rimmed by the goethite veins are always surrounded by radiating cracks in the silicate matrix. Some of those cracks are filled with shock melted silicate glass. Goethite rimming the metal varies widely in size from few microns down to a fraction of a micron. In crossed polarizers it shows the typical red internal
413
reflections. Electron microprobe analyses of areas believed to be homogeneous indicate Fe to be the major element with appreciable amounts of Ni, C1 and some traces of S and K. The probe analyses revealed a quite variable composition probably indicating that the analyzed areas are indeed submicroscopic mixture of goethite and other compounds of uncertain nature (table 2). All analyzed goethite areas indicate an NiO content varying between 1.64 and 5.71%. The chlorine content was found in some analyzed areas to be significantly high (up to 4.18%). Although the presence of fine grained lawrencite is not excluded, as we shall see later, other chlorine compounds may be responsible for the high local C1 concentration. In order to learn about the nature of the sulfur bearing compound, if it is a submicroscopic sulfide or a sulfate mixed with goethite, or about the bonding nature of S present in the goethite structure, we determined the positions of the K a line of sulfur in a troilite and a baryte standard and in lunar goethite. Our probe scans revealed the following values for S Ka in troilite, baryte, and goethite respectively 5.3766 A, 5.3737 A and 5.3732 A. Our probe measurements indicate that the sulfur in goethite or in the compound mixed with goethite is very probably bound as a sulfate and not as a sulfide. (2) The second assemblage in which goethite occurs is unique in the lunar samples. This assemblage consists of troilite, goethite, sphalerite, two zinc and chlorine rich phases and a Pb rich phase. Many of the troilite grains in this sample show different degrees o f shock from simple cracking up to severe crushing, undulose extinction and stress twinning. Along its grain
Table 2 Electron microprobe analyses of goethites from sample no. 66095,89 1
2
3
4
5
6
7
73.29
73.34
81.14
70.40
74.20
86.20
81.75
NiO
4.44
2.84
3.25
4.32
4.74
5.71
1.64
Fe203 MnO
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
CI
1.86
1.00
1.16
0.90
2.74
3.40
4.18
P2Os
0.07
0.28
0.62
0.49
0.41
0.38
0.37
SO3
0.40
0.24
0.71
0.29
0.15
1.18
0.33
K20
0.09
0.21
0.05
0.27
0.05
0.03
0.03
Total
80.15
77.91
86.93
76.67
82.29
96.90
88.30
414
A. El Goresy et al., Zn, Pb, Cl and FeOOH-bearing assemblages in the Apollo 16 Sample 66095
Table 4 Electron microprobe analyses of sphalerites from sample no. 66095,89 1
2
3
Fe Mn S
44.5 17.4 n.d. 31.4
46.9 11.8 n.d. 31.7
45.4 19.0 0.04 30.5
Total
93.3
89.4
94.94
Zn
Fig. 4. Shocked troilite grain (Tr) replaced along its boundaries and along cracks by sphalerite (Sp) and goethite (G). Phases X 1 and X2 (X) are associated with sphalerite. Reflected light. boundaries and its cracks these troilite grains are replaced b y a grey phase with high refiectivity compared to goethite. This phase is tentatively identified as sphalerite (Sp in fig. 4). Both troilite and sphalerite are surrounded by goethite (G) and other two grey phases (X in fig. 4). Electron microprobe analyses were carried out on the coexisting phases o f this assemblage. The composition of troilite is given in table 3. Troilite contains traces of Zn up to 0.07% while other grains not coexisting with this assemblage are barren of Zn. Table 4 shows the composition of three sphalerite grains leaving no doubt that the mineral is an iron rich zinc
sulfide. The low totals are due to the extreme small size of grains analyzed (one micron and smaller). This is the first report o f sphalerite in lunar samples. Fig. 5 shows a troilite grain which is replaced along its boundaries by sphalerite (Sp). Both minerals are surrounded by goethite (G) and other dark grey phases (marked by X). Electron microprobe analyses of these phases indicate that at least two chemically distinct phases are present. In reflected light both phases are identical in color and reflectivity. The reflectivity of both phases is slightly higher than that o f fayalite. We do not know if these phases are opaque or transparent. Under the electron beam the phases were found to breakdown slowly even if low specimen currents and low acceleration energy are employed. F o r this reason we were restricted to fast semi-quantitative analyses using an Li drifted Slsolid state detector attached to our electron microprobe. The spectrum recovered for
Table 3 Electron microprobe analyses of troilites from sample no. 66O95,89 1
Fe Zn Ni S
2
3
4
63.7 0.02 0.01 36.5
63.5 0.03 0.03 36.6
63.6 0.03 0.03 36.4
Total 100.23
100.16
100.06
63.0 0.07 n.d. 36.6
5
6
63.5 0.01 0.06 36.7
63.6 n.d. 0.11 36.2
99.67 100.27
99.91
Analyses: 1 - 5 coexisting with sphalerite; 6 without sphalerite or goethite.
Fig. 5. Troilite (Tr) is rimmed by sphalerite (Sp), goethite (G) and Zn and C1 bearing sulfates (X). Reflected light.
A. El Goresy et al., Zn, Pb, Cl and FeOOH-bearing assemblages in the Apollo 16 Sample 66095
> Si
(Li)
DETECTOR
RESOLUTION SAMF3t-E
165 e V
4"
NO. 6 6 0 9 5 , 8 9
Y
i.t >
#,
d x ~
>
tO d
2
t!~
;"
> > o
>
,,:>
I
,~
>
z
~
,,;
F-.
u.
~
v
,:,;
-
Z
n
z
Fig. 6. Energy dispersive spectrum of phase X 1, displaying the emission spectra of S, CI, Ti, Fe, Ni and Zn.
Si
(I..-i) D E T E C T O R
RESOLUTION SAMEE
165 e V
No. 66095,89
> >
>~*~ o ~ d d
>
>
>~ "g
o
.~ >
Fig. 7. Energy dispersive spectrum of phase X2 showing emission lines of Si, P, S, C1, K, Ca, Fe, Ni and Zn.
415
416
A. El Goresy et al., Zn, Pb, CI and FeOOH-bearing assemblages in the Apollo 16 Sample 66095
> ..g
Si
(Li)
DETECTOFI
RESOLUTION SAMPLE
165 e V
li
5~
N o . 6ti095,89
I1.
> ®
>
>
> n
~
d
'¢
,4
~
1
¥ d ¥ 1 1
o
>
j
Fig. 8. Energy dispersive spectrum of FeOOH showing major Fe and minor C1, K, Ca, and Ni. the first phase (designated Xl) is shown on fig. 6. This spectrum displays the typical emission lines of Fe, Ti, Zn, Ni, C1, and S. This phase is probably a Cl-bearing sulfate of Fe, Ti, Zn, and Ni. Quantitative estimation of Zn and Ct contents revealed 8.5% and 2.4%, respectively. Fig. 7 shows the spectrum of phase X 2 indicating the presence of major Fe, P, S, C1, Zn, and Ni with minor K, Ca, and Si. Silicon may partly be due to excitation of neighboring silicates. This phase may be a mixture of a C1 bearing sulfate and a phosphate of Fe, Ni, Zn, K, and Ca. The spectrum of goethite is shown in fig. 8. Compared to X 1 and X 2 no Zn was detected in goethite. The role of chlorine is not well understood. This element may be present in the form of a chloride (?lawrencite) or incorporated in the sulfate or phosphate. In addition to the above described phases minute grains of K-rich glass were found to occur between sphalerite and goethite. Along the boundaries between troilite, sphalerite and goethite a submicroscopic phase with high lead content (0.3-0.4%) was detected with the probe. The present investigations indicate that sphalerite is replacing troilite along grain boundaries and cracks. The textures also indicate (figs. 4 and 5) that sphalerite and very probably goethite are reaction products between Zn and C1 bearing material
(presumably a chloride or a C1 bearing sulfate) and troilite. Although the nature of this material is not known, phases X 1 and X 2 may be remnants of this material. The nature of the Pb-bearing phase is unknown. Lawrencite, if present, was not necessarily present in the breccia before the introduction of the Zn, Pb and C1 bearing solution or gases. We cannot rule out one of the possibilities that lawrencite is either introduced with the Zn, Pb and C1 bearing material or was formed as a reaction product. Due to the complex nature of these assemblages goethite may be formed in one of the following ways or by a combination of the three processes: (1) by breakdown of troilite in a water rich atmosphere (2) by reaction between troilite and material rich in sulfates and chlorides (3) by reaction between lawrencite and water or water vapor. These reactions were probably genetically connected with an impact event causing severe shock features as evidenced by the presence of shock melted silicates and metals as well as crushing and stress twinning of troilite. Williams and Gibson [5] recently discussed the PT conditions required for stability of goethite on the lunar surface. They argue that goethite is stable only at low temperatures and pressures in almost pure H 2 - H20 gases and that goethite
A. El Goresy et aL, Zn, Pb, CI and FeOOH-bearing assemblages in the Apollo 16 Sample 66095
is not stable in carbonaceous gases at low total pressures. They also conclude that gases from impacting carbonaceous material cannot have produced goethite. Their arguments are mainly based on the assumption that goethite is produced from metallic iron or magnetite preexisting in the lunar samples. In a model process Williams and Gibson suggest a reaction at about 930°C between ferrous iron present in the lunar glasses and solar wind hydrogen present in a concentration of 100 ppm yielding about 0.3% of metal and water vapor. If the rocks are cooled below 130°C the stability field of goethite will be entered and metallic iron would react with water to produce goethite + hydrogen. A decrease in pressure would then according to Williams and Gibson drive the system to the goethite - hematite phase boundary. As a result of this process metallic iron would be surrounded by a rim of goethite which, in turn, is surrounded by a rim of hematite. Agrell et al. [6] report that if the goethite bearing sample would be near enough to the lunar surface thus having access to the lunar atmosphere goethite would breakdown to hematite + water vapor. However, neither Agrell et al. nor we observed any traces of hematite surrounding the goethite rims, although Williams and Gibson speculate that the red stainings around goethite in the photomicrograph provided by S. Agrell to them could be hematite resulting from the shift to the goethite-hematite boundary. Our present investigation indicate that the assemblage in which FeOOH occurs is much more complicated than that described by Agrell et al. and than anticipated by Williams and Gibson. Our analyses of goethite indicate appreciable amounts of C1 (0.90 - 4.18%) and SO 3 (0.15 - 1.18%) to be present. This, in fact, in addition to the presence of C1 and Zn rich sulfates and possibly chlorides in the same assemblage indicate that the possibility of the presence of Akaganeite (flFeOOH) or lepidocrocite (TFeOOH) should be considered. Williams and Gibson proposed that chloride and sulfate anions may stabilize the other two FeOOH polymorphs rather than goethite or these large anions or molecules may be trapped within goethite. Hence, the thermodynamic discussion presented by Williams and Gibson probably do not hold for the assemblages described in this paper. In other words FeOOH rich in large ions or molecules like sulfates or chlorides may be indeed stable under PT conditions prevailing on the lunar surface.
417
The mineralogy and chemistry of the goethite bearing assemblages in sample 66095,89 indicate that the formation of FeOOH by reaction between solar wind hydrogen and ferrous iron in lunar glasses at 930°C followed by reactions at low temperatures as proposed by Williams and Gibson cannot be accepted. Formation by fumarolic activity or by impact of a carbonaceous chondrite or a comet are more likely because of strong enrichment in volatile elements. However, we are in favor of an impact process of a water and volatile rich meteorite or a comet for the following reasons: (1) Sample 66095,89 shows different degrees of shock metamorphism ranging from mild up to severe effects such as shock melting of silicates to glass and FeNi blebs originally occurring in the rock to metallic spherules. The sphalerite - goethite - sulfate assemblage is always locally associated with shocked troilire grains. (2) None of the mare basalts studied from other lunar missions show any indication of fumarolic activity or the presence of hydrated mineral. If fumarolic activity took place, it is not clear why vast areas of the lunar surface where volcanic activity took place 4 to 3 billion years ago are barren of these fumaroles, whereas only restricted areas of the highlands should still show rests of this activity. (3) Judging from the size of the reaction rims around metallic FeNi and shocked troilite the water vapor and volatile rich gas activity must have lasted only for a short time which can be explained by an impact process rather than by fumarolic activity. (3) Besides the electron microprobe and microscopic investigation, we have analyzed a 10 × 6 mm area of the thin section 66095,89 for bulk sulfur, chlorine and zinc concentrations, using a Philips Xray fluorescence spectrometer. The intended objective of the S, C1 and Zn analyses was to compare the bulk abundances of these elements with those of known lunar and meteoritic material and to trace the source of S, C1, and Zn in this way. One of the major difficulties faced during the X-ray fluorescence analysis was due to the fact that the sample is partly impregnated and surrounded by the epoxy resin used for mounting. Although we have carefully screened off the surrounding epoxy rim, we could not eliminate the influence of the epoxy veins and spots enclosed
418
A. El Goresy et al., Zn, Pb, CI and FeOOH-bearing assemblages in the Apollo 16 Sample 66095
within the thin section. Blank analyses on an epoxy area revealed detectable amounts of S, C1 and Zn. Nevertheless, we found indications of enriched S, C1 and Zn contents in 66095,89 compared to other thin sections from the Apollo 16 site. The enhancement of these elements is probably due to the exotic mineral assemblages described in the previous section. Based on the mineralogical and shock evidence and the overall low abundances of volatiles in lunar matter we are forced to assume that excess sulfur, chlorine, zinc and water in the goethite stmcture derive from an extralunar source. The incorporation of these elements into the breccia probably ensued by the action of shock waves in the presence of a transient atmosphere which was created by the impact of a volatile rich projectile. A carbonaceous chondrite of type 1 appears to be plausible candidate. These bodies contain about 6 wt%S, up to 800 ppm C1, around 400 ppm Zn and 20 w t % H 2 0 [7]. From our semi-quantitative zinc analysis we estimate a zinc content of about 1 0 0 - 2 0 0 ppm in this sample. The indigenous chlorine and zinc contents of lunar matter do not exceed some tens ppm (Reed et al. [8] ; Morgan et al. [9]). Kr~ihenbiJhl et al. [10] lately also found strongly enhanced zinc and other volatile metal contents in sample 66095,55. In a very recent investigation of orange-colored soil of Apollo 17 unexpectedly high values for zinc and chlorine have been found [11]. Due to the presence of chloride-, sulfates-, zincand goethite-bearing phases in sample 66095,89 the question arises, if not rather a cometary impact than the impact of a carbonaceous chondrite caused the anomalous elemental admixture to 66095. Our present knowledge of elemental abundances in comets is rather scanty. Yet it is not unreasonable to assume that water and chlorine have a higher abundance in comets than in C1 chondrites. At first sight the incorporation of appreciable amounts of projectile material into the target appears surprising because of almost complete evaporation of the projectile mass at high impact velocity. This process certainly applies for dense objects, as iron and stone meteorites. In the case of a low density cometary projectile consisting of a nucleus, coma and tail, and having a high portion of volatile matter, the impact phenomena may be, however, quite differ-
ent in respect to duration, life time of a transient atmosphere and energy distribution. The selective enrichment of volatile metals with dominantly chalcophile geochemical behavior and of sulfur and chlorine in breccia 66095 was probably favored by the chemical reactivity of these elements among each other at the sites of deposition.
3. Conclusions The present investigations indicate that sample 66095,89 is unusually enriched in the volatile elements C1, Zn and Pb. This enrichment probably took place in an impact event very probably of a comet or a carbonaceous chondrite. The enrichment in the volatile elements Zn, Pb and C1 as well as the presence of the assemblage Cl-bearing FeOOH + metallic FeNi and C1 bearing FeOOH + troilite + sphalerite + Fe, Zn, C1, sulfates and the small range of the reaction rims indicate a short range phenomenon. Thus an origin by fumarolic activity or by reaction between solar wind hydrogen and ferrous iron in glass is very unlikely.
Acknowledgements We wish to thank J. Janicke and D. Kaether for their assistance in probe and X-ray fluorescence analyses. The help of H. Weber in drafting of the figures and photomicrographs is gratefully acknowledged.
References [1] Apollo 16 Preliminary Examination Team, A petrographic and chemical description of samples from the lunar highlands (1972) p. 23. [2] F.L. Whipple, Earth, moon and planets (Harvard University Press, 1968) p. 282. [3] J.1. Goldstein, H.J. Axon and C.F. Yen, Metallic particles in the Apollo 14 lunar soil, Proc. Third Lunar Sci. Conf., Suppl. 3, Geochim. Cosmochim. Acta 1 (1972) 1037. [4] J.I. Goldstein and H.J. Axon, Metallic particle from 3 Apollo 15 soils, in: The Apollo 15 lunar samples, J.W. Chamberlain and C. Watkins, eds. (Lunar Science Institute, 1972), p. 78-81. [5] R.J. Williams and E.K. Gibson, The origin and stability of lunar goethite, hematite and magnetite, Earth Planet. Sci. Letters 17 (1972) 84.
A. El Goresy et al., Zn, Pb, CI and FeOOH-bearing assemblages in the Apollo 16 Sample 66095 [6] S.O. Agrell, J.H. Scoon, J.V. Long and J.N. Coles, The occurrence of goethite in a microbreccia from Fra Mauro Formation, in: Lunar Science, vol. III, C. Watkins, ed. (Lunar Science Institute, Contr. No. 88, 1972) p. 7. [7] B. Mason, Handbook of elemental abundances in meteorites (Gordon and Breach, 1971). [8] G.W. Reed, Jr., S. Jovanovic and L. Fuchs, Trace element relations between Apollo 14 and 15 and other lunar samples, and the implications of a moon-wide C1KREEP coherence and PT-metal noncoherence, Proc. Third Lunar Sci. Conf., Suppl. 3, Geochim. Cosmochim. Acta 2 (1972) 1989.
419
[9] J.W. Morgan, J.C. Laul, U. Krahenbt~hl, R. Ganapathy and E. Anders, Major impacts on the moon: Characterization from trace elements in Apollo 12 and 14 samples, Proc. Third Lunar Sci. Conf., Suppl. 3, Geochim. Cosmochim. Acta 2 (1972) 1377. [10] U. Kr~ahenbi~hl, R. Ganapathy, J.W. Morgan and E. Anders, Volatile elements in Apollo 16 samples: Possible evidence for outgassing of the moon, Science (1973) in press. [11] Aviation Week and Space Technology, January 15, (1973).
[]
ZINC, LEAD, CHLORINE
AND FeOOH-BEARING
ASSEMBLAGES
IN THE APOLLO
16
SAMPLE 66095: ORIGIN BY IMPACT OF A COMET OR A CARBONACEOUS
CHONDRITE?
A. E1 GORESY, P. RAMDOHR, M. PAVI~E W I~ :~ , O. MEDENBACH, O. MOLLER and W. GENTNER Max.Planck.lnstitut ffir Kernphysik, HeMelberg, Germany Received 2 February 1973 Revised version received 19 February 1973 Sample 66095,89 collected from station 6 from the lunar Highlands in the Descartes Site shows evidence of mild to severe shock. These shock features are accompanied by an unusual enrichment in the volatile elements C1, Zn and Pb and by the presence of FeOOH. FeOOH occurs in two distinct assemblages: (l) with metallic FeNi, (2) with troilite, sphalerite and two CI bearing Zn, Fe sulfates. Lead is present exclusively in the second assemblage at the boundaries between troilite and goethite. Lead concentrations up to 0.4% were found. However, the nature of lead-bearing phase is unknown. X-ray fluorescence analyses of a 10 X 6 mm area of the thin section also yielded enhanced chlorine, sulfur and zinc contents. The formation of this unique assemblage and the introduction of the material rich in volatile elements is very probably genetically connected with an impact of a carbonaceous chondrite or a comet. The small range of the reaction between the volatile rich gases and metallic FeNi and troilite indicate a short-live-phenomenon and thus fumarolic activity is a very unlikely process.
1. Introduction Study o f lunar samples recovered during Apollo and Luna missions demonstrated that the lunar rocks are depleted in water, volatile compounds and that trivalent iron is absent in many lunar minerals. Of the rocks collected during tile Apollo 16 mission one sample, 66095 collected from station 6 near South Ray Crater proved to be unique among the recovered Apollo 16 rocks. Rusty areas consisting of goethite were observed to occur around original components [1]. I f goethite is formed on the lunar surface then we have to consider the possibility o f water release from deeper regions o f the moon or goethite formation by oxidation of preexisting minerals due to an impact of a water bearing body presumably a carbonaceous chondrite or a comet. Whipple's * Present address: Institut Za Bakar, Bor, Yugoslavia.
theory [2] that comets are fundamentally balls o f ice and dirt is now widely accepted. In this report we are presenting mineralogical and chemical evidence that FeOOH in sample 66095,89 is formed on the lunar surface probably by impact of an object rich in the volatile elements Zn, Pb, C1, and water. The present investigations did not establish the nature of FeOOH compound present in this sample if it is goethite, akaganeite or lepidocrocite. In this paper we are going to call this compound for simplicity goethite until its nature is clarified. Sample 66095,89 allocated to us is a high grade metamorphic breccia o f type III according to the petrographic classification o f the PET-report [1]. The sample is heavily shocked and is penetrated by several veins filled with shock melted silicate glass containing thousands o f metallic spherules. The opaque minerals observed in the plagioclase rich groundmass are: metallic FeNi, troilite, schreibersite, cohenite sphalerite, ilmenite, baddeleyite, goethite, different Zn, C1 and S bearing
412
A. El Goresy et aL, Zn, Pb, CI and FeOOH-bearing assemblages in the Apollo 16 Sample 66095
phases and a Pb rich phase. Goethite occurs in two distinct exotic assemblages one with metallic FeNi and the other with troilite and sphalerite.
2. Results and discussion
2.1. FeNi metal and schreibersite
Metallic FeNi occurs as large blebs up to 1 mm in size sporadically distributed in the silicate matrix and as metallic spherules in the shock produced silicate glass veins. Both metal blebs and spherules are optically and chemically one metallic phase of kamacite composition. Electron microprobe analyses of numerous grains indicate narrow compositional variation. Furthermore, no difference in chemistry was found to exist between metal blebs in the silicate groundmass and spherules in the glass veins. These findings indicate that the spherules are formed by shock melting of preexisting metal blebs. Both metals have an average composition o f 94.3% Fe, 5.51% Ni, 0.37% Co, and 0.14% P. Fig. 1 shows the Ni content versus Co content o f all grains analyzed. Using the criteria set forward by Goldstein et al. [3, 4] the present findings indicate that the FeNi metals in sample 66095,89 fall within the meteoritic composition. In composition and structure they are also J
2.8 ~ J 2.~
66095,89
2.0 1.6
~ J
2 12.
J
5
similar to phosphide-metal particles described by Goldstein et al. [3] from the Apollo 12 landing site. The metals encountered in this sample are very probably meteoritic debris incorporated in the breccia long before solidification and metamorphism. However, the very narrow composition of the metals is striking. Several metal grains were found to contain schreibersite inclusions (fig. 2). As shown in this figure the schreibersite occurs as blebs or small idiomorphic crystals. Numerous schreibersite grains were analyzed and some selected data are shown in table 1. No apparent compositional variation from grain to grain was observed. The Co-content is quite low compared to that of coexisting kamacite.
J
Table 1 Selected electron microprobe analyses of schreibersites from sample no. 66095,89
8"
0
Fig. 2. A metal particle with schreibersite inclusion (light grey). The metal grained is rimmed by troilite (dark grey). Reflected light.
10
15 20 wt % Ni Fig. 1. Co versus Ni content of metal blebs in the metamorphosed breccia groundmass and metallic spherules in shock melted silicate glass veins. The lower two curves define the composition range of meteoritic metal. The box on the left side defines the low Ni and low Co metals of the Apollo 11 basalts. The upper two curves define the composition of the Apollo 12 metals. The outlines of this diagram are after Goldstein and Axon [4].
1
2
3
4
Fe
66.7
68.5
67.7
68.8
P
14.8
15.0
14.8
14.9
Ni
17.1
15.1
15.9
14.4
Co Total
0.09
0.12
0.08
0.15
98.69
98.72
98.48
98.52
A. El Goresy et aL, Zn, Pb, Cl and FeOOH-bearingassemblages in the Apollo 16 Sample 66095
Fig. 3. Metal blebs cut by several shock melted silicate veins. Photomicrograph shows metallic spherules to be formed by shock melting of preexisting metal. Reflected light. 2.2. Exotic assemblages Two exotic assemblages in which goethite occurs were observed in sample 66095,89: (1) Goethite or at least a goethite rich mixture as reaction rims around metal blebs. The metallic spherules in the shock melted silicate glass veins do not show such goethite reactions (fig. 3). The metal blebs rimmed by the goethite veins are always surrounded by radiating cracks in the silicate matrix. Some of those cracks are filled with shock melted silicate glass. Goethite rimming the metal varies widely in size from few microns down to a fraction of a micron. In crossed polarizers it shows the typical red internal
413
reflections. Electron microprobe analyses of areas believed to be homogeneous indicate Fe to be the major element with appreciable amounts of Ni, C1 and some traces of S and K. The probe analyses revealed a quite variable composition probably indicating that the analyzed areas are indeed submicroscopic mixture of goethite and other compounds of uncertain nature (table 2). All analyzed goethite areas indicate an NiO content varying between 1.64 and 5.71%. The chlorine content was found in some analyzed areas to be significantly high (up to 4.18%). Although the presence of fine grained lawrencite is not excluded, as we shall see later, other chlorine compounds may be responsible for the high local C1 concentration. In order to learn about the nature of the sulfur bearing compound, if it is a submicroscopic sulfide or a sulfate mixed with goethite, or about the bonding nature of S present in the goethite structure, we determined the positions of the K a line of sulfur in a troilite and a baryte standard and in lunar goethite. Our probe scans revealed the following values for S Ka in troilite, baryte, and goethite respectively 5.3766 A, 5.3737 A and 5.3732 A. Our probe measurements indicate that the sulfur in goethite or in the compound mixed with goethite is very probably bound as a sulfate and not as a sulfide. (2) The second assemblage in which goethite occurs is unique in the lunar samples. This assemblage consists of troilite, goethite, sphalerite, two zinc and chlorine rich phases and a Pb rich phase. Many of the troilite grains in this sample show different degrees o f shock from simple cracking up to severe crushing, undulose extinction and stress twinning. Along its grain
Table 2 Electron microprobe analyses of goethites from sample no. 66095,89 1
2
3
4
5
6
7
73.29
73.34
81.14
70.40
74.20
86.20
81.75
NiO
4.44
2.84
3.25
4.32
4.74
5.71
1.64
Fe203 MnO
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
CI
1.86
1.00
1.16
0.90
2.74
3.40
4.18
P2Os
0.07
0.28
0.62
0.49
0.41
0.38
0.37
SO3
0.40
0.24
0.71
0.29
0.15
1.18
0.33
K20
0.09
0.21
0.05
0.27
0.05
0.03
0.03
Total
80.15
77.91
86.93
76.67
82.29
96.90
88.30
414
A. El Goresy et al., Zn, Pb, Cl and FeOOH-bearing assemblages in the Apollo 16 Sample 66095
Table 4 Electron microprobe analyses of sphalerites from sample no. 66095,89 1
2
3
Fe Mn S
44.5 17.4 n.d. 31.4
46.9 11.8 n.d. 31.7
45.4 19.0 0.04 30.5
Total
93.3
89.4
94.94
Zn
Fig. 4. Shocked troilite grain (Tr) replaced along its boundaries and along cracks by sphalerite (Sp) and goethite (G). Phases X 1 and X2 (X) are associated with sphalerite. Reflected light. boundaries and its cracks these troilite grains are replaced b y a grey phase with high refiectivity compared to goethite. This phase is tentatively identified as sphalerite (Sp in fig. 4). Both troilite and sphalerite are surrounded by goethite (G) and other two grey phases (X in fig. 4). Electron microprobe analyses were carried out on the coexisting phases o f this assemblage. The composition of troilite is given in table 3. Troilite contains traces of Zn up to 0.07% while other grains not coexisting with this assemblage are barren of Zn. Table 4 shows the composition of three sphalerite grains leaving no doubt that the mineral is an iron rich zinc
sulfide. The low totals are due to the extreme small size of grains analyzed (one micron and smaller). This is the first report o f sphalerite in lunar samples. Fig. 5 shows a troilite grain which is replaced along its boundaries by sphalerite (Sp). Both minerals are surrounded by goethite (G) and other dark grey phases (marked by X). Electron microprobe analyses of these phases indicate that at least two chemically distinct phases are present. In reflected light both phases are identical in color and reflectivity. The reflectivity of both phases is slightly higher than that o f fayalite. We do not know if these phases are opaque or transparent. Under the electron beam the phases were found to breakdown slowly even if low specimen currents and low acceleration energy are employed. F o r this reason we were restricted to fast semi-quantitative analyses using an Li drifted Slsolid state detector attached to our electron microprobe. The spectrum recovered for
Table 3 Electron microprobe analyses of troilites from sample no. 66O95,89 1
Fe Zn Ni S
2
3
4
63.7 0.02 0.01 36.5
63.5 0.03 0.03 36.6
63.6 0.03 0.03 36.4
Total 100.23
100.16
100.06
63.0 0.07 n.d. 36.6
5
6
63.5 0.01 0.06 36.7
63.6 n.d. 0.11 36.2
99.67 100.27
99.91
Analyses: 1 - 5 coexisting with sphalerite; 6 without sphalerite or goethite.
Fig. 5. Troilite (Tr) is rimmed by sphalerite (Sp), goethite (G) and Zn and C1 bearing sulfates (X). Reflected light.
A. El Goresy et al., Zn, Pb, Cl and FeOOH-bearing assemblages in the Apollo 16 Sample 66095
> Si
(Li)
DETECTOR
RESOLUTION SAMF3t-E
165 e V
4"
NO. 6 6 0 9 5 , 8 9
Y
i.t >
#,
d x ~
>
tO d
2
t!~
;"
> > o
>
,,:>
I
,~
>
z
~
,,;
F-.
u.
~
v
,:,;
-
Z
n
z
Fig. 6. Energy dispersive spectrum of phase X 1, displaying the emission spectra of S, CI, Ti, Fe, Ni and Zn.
Si
(I..-i) D E T E C T O R
RESOLUTION SAMEE
165 e V
No. 66095,89
> >
>~*~ o ~ d d
>
>
>~ "g
o
.~ >
Fig. 7. Energy dispersive spectrum of phase X2 showing emission lines of Si, P, S, C1, K, Ca, Fe, Ni and Zn.
415
416
A. El Goresy et al., Zn, Pb, CI and FeOOH-bearing assemblages in the Apollo 16 Sample 66095
> ..g
Si
(Li)
DETECTOFI
RESOLUTION SAMPLE
165 e V
li
5~
N o . 6ti095,89
I1.
> ®
>
>
> n
~
d
'¢
,4
~
1
¥ d ¥ 1 1
o
>
j
Fig. 8. Energy dispersive spectrum of FeOOH showing major Fe and minor C1, K, Ca, and Ni. the first phase (designated Xl) is shown on fig. 6. This spectrum displays the typical emission lines of Fe, Ti, Zn, Ni, C1, and S. This phase is probably a Cl-bearing sulfate of Fe, Ti, Zn, and Ni. Quantitative estimation of Zn and Ct contents revealed 8.5% and 2.4%, respectively. Fig. 7 shows the spectrum of phase X 2 indicating the presence of major Fe, P, S, C1, Zn, and Ni with minor K, Ca, and Si. Silicon may partly be due to excitation of neighboring silicates. This phase may be a mixture of a C1 bearing sulfate and a phosphate of Fe, Ni, Zn, K, and Ca. The spectrum of goethite is shown in fig. 8. Compared to X 1 and X 2 no Zn was detected in goethite. The role of chlorine is not well understood. This element may be present in the form of a chloride (?lawrencite) or incorporated in the sulfate or phosphate. In addition to the above described phases minute grains of K-rich glass were found to occur between sphalerite and goethite. Along the boundaries between troilite, sphalerite and goethite a submicroscopic phase with high lead content (0.3-0.4%) was detected with the probe. The present investigations indicate that sphalerite is replacing troilite along grain boundaries and cracks. The textures also indicate (figs. 4 and 5) that sphalerite and very probably goethite are reaction products between Zn and C1 bearing material
(presumably a chloride or a C1 bearing sulfate) and troilite. Although the nature of this material is not known, phases X 1 and X 2 may be remnants of this material. The nature of the Pb-bearing phase is unknown. Lawrencite, if present, was not necessarily present in the breccia before the introduction of the Zn, Pb and C1 bearing solution or gases. We cannot rule out one of the possibilities that lawrencite is either introduced with the Zn, Pb and C1 bearing material or was formed as a reaction product. Due to the complex nature of these assemblages goethite may be formed in one of the following ways or by a combination of the three processes: (1) by breakdown of troilite in a water rich atmosphere (2) by reaction between troilite and material rich in sulfates and chlorides (3) by reaction between lawrencite and water or water vapor. These reactions were probably genetically connected with an impact event causing severe shock features as evidenced by the presence of shock melted silicates and metals as well as crushing and stress twinning of troilite. Williams and Gibson [5] recently discussed the PT conditions required for stability of goethite on the lunar surface. They argue that goethite is stable only at low temperatures and pressures in almost pure H 2 - H20 gases and that goethite
A. El Goresy et aL, Zn, Pb, CI and FeOOH-bearing assemblages in the Apollo 16 Sample 66095
is not stable in carbonaceous gases at low total pressures. They also conclude that gases from impacting carbonaceous material cannot have produced goethite. Their arguments are mainly based on the assumption that goethite is produced from metallic iron or magnetite preexisting in the lunar samples. In a model process Williams and Gibson suggest a reaction at about 930°C between ferrous iron present in the lunar glasses and solar wind hydrogen present in a concentration of 100 ppm yielding about 0.3% of metal and water vapor. If the rocks are cooled below 130°C the stability field of goethite will be entered and metallic iron would react with water to produce goethite + hydrogen. A decrease in pressure would then according to Williams and Gibson drive the system to the goethite - hematite phase boundary. As a result of this process metallic iron would be surrounded by a rim of goethite which, in turn, is surrounded by a rim of hematite. Agrell et al. [6] report that if the goethite bearing sample would be near enough to the lunar surface thus having access to the lunar atmosphere goethite would breakdown to hematite + water vapor. However, neither Agrell et al. nor we observed any traces of hematite surrounding the goethite rims, although Williams and Gibson speculate that the red stainings around goethite in the photomicrograph provided by S. Agrell to them could be hematite resulting from the shift to the goethite-hematite boundary. Our present investigation indicate that the assemblage in which FeOOH occurs is much more complicated than that described by Agrell et al. and than anticipated by Williams and Gibson. Our analyses of goethite indicate appreciable amounts of C1 (0.90 - 4.18%) and SO 3 (0.15 - 1.18%) to be present. This, in fact, in addition to the presence of C1 and Zn rich sulfates and possibly chlorides in the same assemblage indicate that the possibility of the presence of Akaganeite (flFeOOH) or lepidocrocite (TFeOOH) should be considered. Williams and Gibson proposed that chloride and sulfate anions may stabilize the other two FeOOH polymorphs rather than goethite or these large anions or molecules may be trapped within goethite. Hence, the thermodynamic discussion presented by Williams and Gibson probably do not hold for the assemblages described in this paper. In other words FeOOH rich in large ions or molecules like sulfates or chlorides may be indeed stable under PT conditions prevailing on the lunar surface.
417
The mineralogy and chemistry of the goethite bearing assemblages in sample 66095,89 indicate that the formation of FeOOH by reaction between solar wind hydrogen and ferrous iron in lunar glasses at 930°C followed by reactions at low temperatures as proposed by Williams and Gibson cannot be accepted. Formation by fumarolic activity or by impact of a carbonaceous chondrite or a comet are more likely because of strong enrichment in volatile elements. However, we are in favor of an impact process of a water and volatile rich meteorite or a comet for the following reasons: (1) Sample 66095,89 shows different degrees of shock metamorphism ranging from mild up to severe effects such as shock melting of silicates to glass and FeNi blebs originally occurring in the rock to metallic spherules. The sphalerite - goethite - sulfate assemblage is always locally associated with shocked troilire grains. (2) None of the mare basalts studied from other lunar missions show any indication of fumarolic activity or the presence of hydrated mineral. If fumarolic activity took place, it is not clear why vast areas of the lunar surface where volcanic activity took place 4 to 3 billion years ago are barren of these fumaroles, whereas only restricted areas of the highlands should still show rests of this activity. (3) Judging from the size of the reaction rims around metallic FeNi and shocked troilite the water vapor and volatile rich gas activity must have lasted only for a short time which can be explained by an impact process rather than by fumarolic activity. (3) Besides the electron microprobe and microscopic investigation, we have analyzed a 10 × 6 mm area of the thin section 66095,89 for bulk sulfur, chlorine and zinc concentrations, using a Philips Xray fluorescence spectrometer. The intended objective of the S, C1 and Zn analyses was to compare the bulk abundances of these elements with those of known lunar and meteoritic material and to trace the source of S, C1, and Zn in this way. One of the major difficulties faced during the X-ray fluorescence analysis was due to the fact that the sample is partly impregnated and surrounded by the epoxy resin used for mounting. Although we have carefully screened off the surrounding epoxy rim, we could not eliminate the influence of the epoxy veins and spots enclosed
418
A. El Goresy et al., Zn, Pb, CI and FeOOH-bearing assemblages in the Apollo 16 Sample 66095
within the thin section. Blank analyses on an epoxy area revealed detectable amounts of S, C1 and Zn. Nevertheless, we found indications of enriched S, C1 and Zn contents in 66095,89 compared to other thin sections from the Apollo 16 site. The enhancement of these elements is probably due to the exotic mineral assemblages described in the previous section. Based on the mineralogical and shock evidence and the overall low abundances of volatiles in lunar matter we are forced to assume that excess sulfur, chlorine, zinc and water in the goethite stmcture derive from an extralunar source. The incorporation of these elements into the breccia probably ensued by the action of shock waves in the presence of a transient atmosphere which was created by the impact of a volatile rich projectile. A carbonaceous chondrite of type 1 appears to be plausible candidate. These bodies contain about 6 wt%S, up to 800 ppm C1, around 400 ppm Zn and 20 w t % H 2 0 [7]. From our semi-quantitative zinc analysis we estimate a zinc content of about 1 0 0 - 2 0 0 ppm in this sample. The indigenous chlorine and zinc contents of lunar matter do not exceed some tens ppm (Reed et al. [8] ; Morgan et al. [9]). Kr~ihenbiJhl et al. [10] lately also found strongly enhanced zinc and other volatile metal contents in sample 66095,55. In a very recent investigation of orange-colored soil of Apollo 17 unexpectedly high values for zinc and chlorine have been found [11]. Due to the presence of chloride-, sulfates-, zincand goethite-bearing phases in sample 66095,89 the question arises, if not rather a cometary impact than the impact of a carbonaceous chondrite caused the anomalous elemental admixture to 66095. Our present knowledge of elemental abundances in comets is rather scanty. Yet it is not unreasonable to assume that water and chlorine have a higher abundance in comets than in C1 chondrites. At first sight the incorporation of appreciable amounts of projectile material into the target appears surprising because of almost complete evaporation of the projectile mass at high impact velocity. This process certainly applies for dense objects, as iron and stone meteorites. In the case of a low density cometary projectile consisting of a nucleus, coma and tail, and having a high portion of volatile matter, the impact phenomena may be, however, quite differ-
ent in respect to duration, life time of a transient atmosphere and energy distribution. The selective enrichment of volatile metals with dominantly chalcophile geochemical behavior and of sulfur and chlorine in breccia 66095 was probably favored by the chemical reactivity of these elements among each other at the sites of deposition.
3. Conclusions The present investigations indicate that sample 66095,89 is unusually enriched in the volatile elements C1, Zn and Pb. This enrichment probably took place in an impact event very probably of a comet or a carbonaceous chondrite. The enrichment in the volatile elements Zn, Pb and C1 as well as the presence of the assemblage Cl-bearing FeOOH + metallic FeNi and C1 bearing FeOOH + troilite + sphalerite + Fe, Zn, C1, sulfates and the small range of the reaction rims indicate a short range phenomenon. Thus an origin by fumarolic activity or by reaction between solar wind hydrogen and ferrous iron in glass is very unlikely.
Acknowledgements We wish to thank J. Janicke and D. Kaether for their assistance in probe and X-ray fluorescence analyses. The help of H. Weber in drafting of the figures and photomicrographs is gratefully acknowledged.
References [1] Apollo 16 Preliminary Examination Team, A petrographic and chemical description of samples from the lunar highlands (1972) p. 23. [2] F.L. Whipple, Earth, moon and planets (Harvard University Press, 1968) p. 282. [3] J.1. Goldstein, H.J. Axon and C.F. Yen, Metallic particles in the Apollo 14 lunar soil, Proc. Third Lunar Sci. Conf., Suppl. 3, Geochim. Cosmochim. Acta 1 (1972) 1037. [4] J.I. Goldstein and H.J. Axon, Metallic particle from 3 Apollo 15 soils, in: The Apollo 15 lunar samples, J.W. Chamberlain and C. Watkins, eds. (Lunar Science Institute, 1972), p. 78-81. [5] R.J. Williams and E.K. Gibson, The origin and stability of lunar goethite, hematite and magnetite, Earth Planet. Sci. Letters 17 (1972) 84.
A. El Goresy et al., Zn, Pb, CI and FeOOH-bearing assemblages in the Apollo 16 Sample 66095 [6] S.O. Agrell, J.H. Scoon, J.V. Long and J.N. Coles, The occurrence of goethite in a microbreccia from Fra Mauro Formation, in: Lunar Science, vol. III, C. Watkins, ed. (Lunar Science Institute, Contr. No. 88, 1972) p. 7. [7] B. Mason, Handbook of elemental abundances in meteorites (Gordon and Breach, 1971). [8] G.W. Reed, Jr., S. Jovanovic and L. Fuchs, Trace element relations between Apollo 14 and 15 and other lunar samples, and the implications of a moon-wide C1KREEP coherence and PT-metal noncoherence, Proc. Third Lunar Sci. Conf., Suppl. 3, Geochim. Cosmochim. Acta 2 (1972) 1989.
419
[9] J.W. Morgan, J.C. Laul, U. Krahenbt~hl, R. Ganapathy and E. Anders, Major impacts on the moon: Characterization from trace elements in Apollo 12 and 14 samples, Proc. Third Lunar Sci. Conf., Suppl. 3, Geochim. Cosmochim. Acta 2 (1972) 1377. [10] U. Kr~ahenbi~hl, R. Ganapathy, J.W. Morgan and E. Anders, Volatile elements in Apollo 16 samples: Possible evidence for outgassing of the moon, Science (1973) in press. [11] Aviation Week and Space Technology, January 15, (1973).