Lunar and Martian Meteorites

The importance of searching for meteorites on the East Antarctic ice sheet was widely recognized in 1983 after it became known that the small and inconspicuous rock sample in Fig. 18.23 that was collected by Ian Whillans and John Schutt on one of the ice fields 

In subsequent years, the meteorite collectors of ANSMET have found many more lunar meteorites on the icefields adjacent to the Transantarctic Mountains while Japanese investigators recovered ten additional specimens of lunar rocks from the large icefields associated with the Yamato Mountains near the coast of East Antarctica. The lunar meteorites that have been collected in Antarctica are listed in Appendix 18.12.3 (see also Cassidy 2003 Table 7.1). The total mass of the lunar meteorites collected in Antarctica is greater than 2,580 g and continues to increase as additional specimens are recovered. 

Prior to the recovery of ALHA 81005, the ANSMET group had collected two other unusual meteorites (ALHA 77005 and EETA 79001) one of which is shown in Fig. 18.24. The mineralogical composition 

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Planets 10 Lunar and martian meteorites, planetary bulk composition Exoplanets ... 

Numerous authors (e.g., Warren, 1994 Wieler, 2002 Nyquist et al., 2001) have contrasted the exposure histories and other properties of lunar and martian meteorites. On average, we would expect key systematic differences to relate to their respective distances from the Earth (or more precisely how easily their ejecta could attain Earth-crossing orbits), the respective depths of their gravitational wells, the mechanical properties of their regoliths, and the relative fluxes of impacting bodies. 

Warren P. (1994) Lunar and Martian meteorite delivery services. Icarus 111, 338-353. 

Lunar and Martian meteorites. At the time of this writing, our collections contain about 20 individual meteorites (corrected for pairings) from the Moon and 18 from Mars. A list of the Martian meteorites is given by Swindle (2002b), who also briefly discusses their cosmic ray record. Exposure ages of Martian meteorites are also compiled and... 

Fig. 3.3 Three oxygen isotope plot of lunar and Martian rocks and HED meteorites supposed to be fragnments of asteroid Vesta (after Wiechert et al. 2003)...

Plots of uranium versus lanthanum (two refractory elements), and potassium versus lanthanum (a volatile element and a refractory element) for terrestrial and lunar basalts, HED achondrites (Vesta), and Martian meteorites. All three elements are incompatible elements and thus fractionate together, so their ratios remain constant. However, ratios of incompatible elements with different volatilities ( /La) reveal different degrees of volatile element depletion in differentiated bodies. After Wanke and Dreibus (1988). 

The W isotopic compositions of various terrestrial samples, chondrites, iron meteorites, basaltic achondrites, lunar samples, and Martian meteorites are expressed as deviations in parts per 104 from the value for the silicate earth (such as the W in a drill bit or chisel), which are the same as those of average solar system materials, represented by carbonaceous chondrites. These values are summarized in Fig. 8.9, from which it can be seen that early segregated metals such as the iron meteorites and metals from ordinary chondrites have only unradiogenic W because they formed early with low Hf/W. The time differences between metal objects segregated from parents with chondritic Hf/W are revealed by the differences in W isotopic compositions between each of the metal objects and chondrites. The Hf-W model ages of all these metals indicate that all of their parent bodies formed within a few million years, implying rapid accretion in the early history of the solar system. 

Figure 5 Plot of variations in (which arise from the decay of the extinct nuclide versus time expressed as ppm differences from present-day compositions. An initial Stn/ Sm = 0.007 is assumed (Prinzhofer et al., 1992). If an LREE-depleted mantle (high Sm/Nd) formed within the first 200-300Ma of Earth history, then with the current 5-10 ppm analytical precision, a positive Nd deviation would be expected to be observed in any sample derived from this source. Lunar samples (Nyquist et al, 1995) and martian meteorites (Harper et al., 1995) show clear evidence of Nd variations reflecting very early differentiation on these bodies. Nd anomalies have now been suggested for some 3.7-3.S Ga terrestrial samples from southwest Greenland (Harper and Jacobsen, 1992 Boyet et al, 2002 Caro et al., 2003). Most of the 3.8 Ga gneisses that have been measured do not show these effects and recent re-measurement of the original Harper and Jacobsen sample by Papanastassiou et al. (2003) has not confirmed the original result (see text). The different/curves are for different degrees of depletion (20% and 40%) of...

As they are with terrestrial, lunar and asteroidal meteorite samples, noble gases have been crucial to deciphering the chronology of the Martian meteorites. However, just as in those other samples, noble gases are not the only chronometers that have been applied. Most of the information about crystallization ages has come from other chronometers. Nyquist et al. (2001) have reviewed the subject, and their best estimates of the formation ages of the Martian meteorites are listed in Table 1 and plotted in Figure 6. 

Scientific literature on the geochemistry of the Moon and Mars is voluminous, and we can only provide overviews of some of the more recent data and current understanding. Lunar samples, lunar meteorites, and Martian (SNC) meteorites were briefly described in... 

The angrites are basaltic in composition, and critically silica undersaturated—all have normative olivine, Ca2Si04, and nepheline and lack orthopyroxene (Mittlefehldt et al., 2002). Angrites are also characterized by extreme depletions in moderately volatile elements (Figure 1). They have very low abundances of all the alkali elements, and have Ga/Al ratios lower than for any other achondrite, lunar sample, or martian meteorite... 

CRE age distributions have become more convincing. Further, the world s collection of meteorites collection has become more diverse. In this respect, the lunar and the martian meteorites take pride of place but leave ample room for R, CH, and CB chondrites, new angrites, and other unusual specimens. At the same time, better experimental methods have lowered detection limits for cosmogenic nuclides and the modeling calculations needed to interpret the measurements have improved. 

More martian than lunar meteorites appear to have come to Earth per crater. According to Mileikowsky et al. (2000), the total mass of the ejecta increases with the size of the impact event. With more energy required for launch from Mars, and with launches rare, a greater likelihood of the pairing of source craters for martian meteorites seems reasonable. 

The numbers of lunar and of martian meteorites are nearly equal. The near equality at first seems odd in light of the closeness and smaller gravitational field of the Moon. The absolute... 

Dhofar 019 Martian meteorite. Lunar Planet. Set XXXIII, 1366. Lunar and Planetary Institute, Houston (CD-ROM). 

Nishiizumi K., Okazaki R., Park J., Nagao K., Masarik J., and Finkel R. C. (2002) Exposure and terrestrial histories of Dhofar 019 martian meteorite. In Lunar Planet. Sci. XXXIII, 1366. The Lunar and Planetary Institute, Houston (CD-ROM). 

Wang, A., Kuebler, K.E., Jolliff, B.L. Haskin, L.A. (2003) Fe-Ti-Cr oxides in Martian meteorite EETA 740001 studied by point counting procedure using Raman spectroscopy. Abstract 1742, 34th Lunar and Planetary Science Conference, League City, TX. 

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