![]() They are rare examples of the earliest stages of mare volcanism and can provide information about how the style of mare volcanism evolved, for example whether there were early mare composition magmas with deep origins. ![]() Both of these rocks crystallized at ∼3.94 Ga, long before most other mare basalts and shortly before the end of the period of intense bombardment. Two of these meteorites are unbrecciated basaltic igneous rocks and might be the products of a single source crater on the Moon. The basaltic lunar meteorites are derived from the mare regions. The high Ir/Ni ratio in Apollo samples has now been interpreted as local heterogeneity on the central nearside, perhaps as a result of impact of a large iron meteorite. However, siderophile abundances and the Ir/Ni ratio in lunar meteorites are significantly lower than in the Apollo samples. High siderophile element abundances and a high Ir/Ni ratio in Apollo 14 and 16 samples have been used as evidence for a high Ni content for the lunar mantle, an Earthlike feature that would be consistent with derivation of the Moon by some sort of Earth fission, a model that is no longer popular. Siderophile element abundances in lunar highlands meteorites have an important bearing on models for lunar core formation. The bulk Al 2O 3 content of about 26 wt% argues in favor of a magma ocean model for formation of the crust, in which the upper crust became enriched in Al 2O 3 by flotation of plagioclase over a primordial intrusion of global extent. For example, the bulk composition of the lunar crust can be estimated from the compositions of the lunar highlands meteorites and the Apollo samples. Lunar highlands meteorites play an important role in interpreting the geological evolution of the Moon. The exterior of the stone is covered in fusion crust, a thin melted zone that was formed when the meteorite fell through the Earth's atmosphere. Lunar meteorite ALHA81005, a lunar highlands breccia, showing a clastic texture. Their oxygen isotopic ratios match those of the Earth/Moon system, and their Fe/Mn ratios and other trace elements, as well as their mineralogy and textures, are similar to those of comparable Apollo and Luna samples.įIGURE 11. ![]() Several lines of evidence show that these meteorites come from the Moon. ![]() In comparison, the Apollo and Luna missions sampled only a relatively small equatorial region of the near side. Although the mass is small, the scientific importance of the lunar meteorites is that they sample the lunar surface randomly and represent several different source sites distinct from the Apollo sites, including the possibility that they sample the far side of the Moon. In terms of the lunar sample suite that is available for scientific study, the total mass of lunar meteorites is about 2.6 kg, compared with the total material returned by the Apollo and Luna missions of 382 kg and 300 g, respectively. They include samples of anorthositic breccias from the lunar highlands and basaltic breccias and rocks from the mare regions, i.e., they represent the major rock types of the lunar surface. The lunar meteorites are the only group of meteorites for which the source body has been identified unequivocally. Jones, in Encyclopedia of Physical Science and Technology (Third Edition), 2003 IX.B Lunar Meteorites Most importantly, meteorites are on Earth available for laboratory study by the simplest to the most sophisticated analytical techniques. Meteorites also constitute important “ground truth” in a chemical and physical sense, critical to interpreting planetary data obtained by remote sensing. Some contain inclusions created before solar system formation others contain organic matter produced on grain boundaries in the early nebula and/or in giant interstellar clouds. Meteorites record certain solar and galactic effects, and yield otherwise unobtainable data relevant to the genesis, evolution, and composition of the Earth other major planets, satellites, and asteroids and the Sun. Meteorites, the “Poor Man's Space Probe”, are important because they contain the oldest solar system materials for research, and sample a wide range of parent bodies-exteriors and interiors-some primitive, some highly evolved. Lipschutz, Ludolf Schultz, in Encyclopedia of the Solar System (Third Edition), 2014 Abstract ![]()
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