Lunar samples

It is hardly necessary to comment on the epic flight of three American astronauts in Apollo 11 which resulted in their return to earth on the 24th July, 1969, with the first 22 kilograms of lunar material. These samples were distributed to scientists in nine countries for one of the most intensive investigations ever prepared, and all the preliminary results were published simultaneously in a special issue of Science in January 1970. 

The likelihood of finding iron in the surface rocks had prompted the adoption of Mossbauer spectroscopy as anon-destructive method of analysis. Such measurements, usually in conjunction with microscopic mineralogical studies, were made on different samples by three laboratories in the U.S.A. and two in England. These are described below individually because of the variations in constitution of the samples. The reference numbers quoted were assigned by the NASA Lunar Receiving Laboratory at Houston, Texas. 

A number of the documented rock samples were examined by Mossbauer scattering methods. Specimens 10020,20 and 10003,22 both contained ilmenite and silicates, although the dominance of pyroxene in the latter sample resulted in narrower resonance lines. Breccia 10065 proved essentially similar to the fines, as indeed expected if they originate as shock lithified fines. 

An important point is the failure to identify any high-spin Fe + cations to within, a few per cent. 

with troilite being seen in the other three. The distribution of these magnetic materials in the rocks was ascertained by microscopic examination. 

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Among the rarest of all meteorites are the lunar meteorites. Isotopic, mineralogical, and compositional properties of these samples provide positive identification as lunar samples because of the unique properties of lunar materials that have been discovered by extensive analyses of lunar materials returned by the manned ApoUo and unstaffed Luna missions. AH but one of the lunar meteorites that have been found to date have been recovered from Antarctica. 

A collision with a Mars-sized object may have resulted in the formation of the Earth s moon. Our moon is by no means the largest satellite in the solar system, but it is unusual in that it and the moon of Pluto are the largest moons relative the mass of the planets they orbit. Geochemical studies of returned lunar samples have shown that close similarities exist between the bulk composition of the moon and the Earth s mantle. In particular, the abimdances of sidero-... 

An example is shown in figure 1 of the molecular interferences which must be dealt with around mass 87 if one wishes to use a mass spectrometer for rubidium/strontium measurements in a geological sample [22]. The major elements in this lunar sample all have mass numbers less than 48. Thus, the mass 87 region should be completely free of atomic peaks except for the minor components such as rubidium and strontium. This is clearly not the case and at most mass numbers in the rubidium region there are major interferences from molecules. 

Regnier, S., Hohenberg, C. M., Marti, K., and Reedy, R. C., "Predicted versus observed cosmic-ray-produced noble gases in lunar samples Improved Kr production ratios", Proc. Lunar Planet. Sci. Conf., 10th, 1979, 1565-1586. 

Marti, K. and Lugmair, G. W., "81Kr-Kr and K-40Ar ages, cosmic-ray spallation products and neutron effects in lunar samples from Oceanus Procell arum", Proc. Second Lunar Sci. Conf., 1971, 2, 1591-1605. 

A focused laser beam of 0.2 joules per pulse is capable of releasing rare gases from well defined 10-100 pm size spots on a polished surface. As a result, it is possible to extend rare gas mass spectrometry to the region of less than 1 pg samples. The technique was first applied to the study of complex lunar samples by George Megrue [2]. 

Substantial abundance anomalies occur among the heavy oxygen isotopes 170 and 180, which are underabundant by up to about 4 per cent relative to 160 in oxide grains of certain of the CAIs, compared with the bulk composition in which the isotope ratios are closer to a terrestrial standard. The intriguing feature of these anomalous ratios is that, in common with some other meteorites, but in contrast to terrestrial and lunar samples, the relative deviations of the two heavy isotopes are equal most normal fractionation processes would cause 180 to have twice the anomaly of 170, as indeed is observed in terrestrial samples and more differentiated meteorites, where the anomalies are also usually much smaller. While there has been speculation that there might be a substantial admixture of pure 160 from a supernova, there are fractionation mechanisms that may be able to account for the effect, e.g. photo-dissociation of molecules affected by selfshielding (R. Clayton 2002). In this case, it is possible that the terrestrial standard is enriched in the heavy O-isotopes while the inclusions have more nearly the true solar ratio. 

Stable isotope analysis of earth, moon and meteorite samples has provided important information concerning the origin of the solar system. Lunar samples returned to earth during the Apollo missions show 8170 and 8lsO enrichment patterns which are virtually identical to those of earth-bound rocks and minerals. On 3-isotope plots like those in Figs. 9.5 and 14.3, a uniform isotope reservoir is represented by a single... 

Leya I, Wider R, Halliday AN (2000) Cosmic-ray production of tungsten isotopes in lunar samples and meteorites and its implications for Hf-W cosmochemistry. Earth Planet Sci Lett 175 1-12 Loss RD, Lugmair GW (1990) Zinc isotope anomalies in Allende meteorite inclusions. Astrophys J 360 L59-L62... 

Swindle TD, Podosek FA (1988) Iodine-Xenon dating. In Meteorites and the Early Solar System. Kerridge JF and Matthews MS (eds) University of Arizona Press, Tucson, p 1114-1146 Tang M, Lewis RS, Anders E (1988) Isotopic anomalies of Ne, Xe, and C in meteorites. I. Separation of carriers by density and chemical resistance. Geochim Cosmochim Acta 52 1221-1234 Tera F, Eugster O, Burnett DS, Wasserburg GJ (1970) Comparative study of Li, Na, K, Rb, Cs, Ca, Sr and Ba abundances in achondrites and in Apollo 11 lunar samples. Geochim Cosmochim Acta Suppl 1 1637-1657... 

Volatile metal chelates are also useful in determining isotope ratios of geological interest, e.g., the Zr/Hf ratio (197). This method proved invaluable as a microtechnique for chromium isotope analysis of lunar samples from the Apollo program (198). 

Cosmochemistry is the study of the chemical composition of the universe and the processes that produced those compositions. This is a tall order, to be sure. Understandably, cosmochemistry focuses primarily on the objects in our own solar system, because that is where we have direct access to the most chemical information. That part of cosmochemistry encompasses the compositions of the Sun, its retinue of planets and their satellites, the almost innumerable asteroids and comets, and the smaller samples (meteorites, interplanetary dust particles or IDPs, returned lunar samples) derived from them. From their chemistry, determined by laboratory measurements of samples or by various remote-sensing techniques, cosmochemists try to unravel the processes that formed or affected them and to fix the chronology of these events. Meteorites offer a unique window on the solar nebula - the disk-shaped cocoon of gas and dust that enveloped the early Sun some 4.57 billion years ago, and from which planetesimals and planets accreted (Fig. 1.1). 

Both wet chemistry and X-ray fluorescence require relatively large samples, typically at least a gram. As scientists prepared for the arrival of the Apollo lunar samples, they developed... 

The Apollo astronauts returned 382 kg of lunar sample to Earth, and this collection was supplemented by 326 g of soil samples collected by the Soviet Luna landers. The first lunar meteorite was found in 1982 in Antarctica. Since that time, over 120 lunar meteorites representing about 60 different fall events have been collected. The total mass of these meteorites is -48 kg. About one-third of these meteorites were recovered in Antarctica by American and Japanese teams, and most of the rest were recovered in the deserts of North Africa and Oman. The lunar meteorites have significantly expanded the areas of the Moon from which we have samples. 

Oxygen isotopes in achondrites (above) and primitive achondrites (below). The 8 notation and units are explained in the caption for Figure 6.4. Most achondrites define mass fractionation lines parallel to, but slightly offset from the terrestrial line. Aubrites and lunar samples plot squarely on the terrestrial line. Primitive achondrites generally do not define oxygen mass fractionation lines, but are scattered and resemble their chondrite precursors. 

Summary of radiometric ages for lunar samples, based on a variety of isotope chronometers. 

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