Fresh fracture surfaces of the martian meteorite ALH84001 contain abundant polycyclic aromatic hydrocarbons (PAHs). These fresh fracture surfaces also display carbonate globules. Contamination studies suggest that the PAHs are indigenous to the meteorite. High-resolution scanning and transmission electron microscopy study of surface textures and internal structures of selected carbonate globules show that the globules contain fine-grained, secondary phases of single-domain magnetite and Fe-sulfides. The carbonate globules are similar in texture and size to some terrestrial bacterially induced carbonate precipitates. Although inorganic formation is possible, formation of the globules by biogenic processes could explain many of the observed features, including the PAHs. The PAHs, the carbonate globules, and their associated secondary mineral phases and textures could thus be fossil remains of a past martian biota.

Abstract— Using new techniques to examine the products of space weathering of lunar soils, we demonstrate that nanophase reduced iron (npFe0) is produced on the surface of grains by a combination of vapor deposition and irradiation effects. The optical properties of soils (both measured and modeled) are shown to be highly dependent on the cumulative amount of npFe0, which varies with different starting materials and the energetics of different parts of the solar system. The measured properties of intermediate albedo asteroids, the abundant S‐type asteroids in particular, are shown to directly mimic the effects predicted for small amounts of npFe0 on grains of an ordinary chondrite regolith. This measurement and characterization of space weathering products seems to remove a final obstacle hindering a link between the abundant ordinary chondrite meteorites and common asteroids.

Abstract-Spaceweathering processes that operate in the lunar regolith modify the surfaces of lunar soil grains. Transmission electron microscope analysis of the lunar soil grains from the fine size fraction of several lunar soils show that most grains are surrounded by thin nm thick) rims. The microstructure and chemical compositions of the rims can be used to classify rims into four broad categories: amorphous, inclusion-rich, multiple, and vesicular. Amorphous rims are noncrystalline, generally lack crystalline inclusions, show evidence for preferential sputtering of cations, and are produced largely by solar-wind irradiation damage. Inclusion-rich rims contain abundant nanometer-sized grains of Fe metal as randomly dispersed inclusions or as distinct layers embedded in an amorphous silica-rich matrix. Inclusion-rich rims are compositionally distinct from their host grains and typically contain accumulations of elements that are not indigenous to the host. Inclusion-rich rims are formed largely by the deposition of impact-generated vapors with a contribution from the deposition of sputtered ions. A continuum in the chemical and microstructuralproperties exists between typical amorphous rims and typical inclusion-rich rims. Multiple-rims consist of a distinct radiation-damaged layer up to SO nm thick, that is overlain by vapor-deposited material of comparable thickness. Vesicular rims are compositionally similar to their hosts and are characterized by an abundance of small (<50 nm in diameter) vesicles concentrated in the outer 100 nm of the rims. The formation of vesicular rims is apparently due to the evolution of solar-wind implanted gases in response to a pulse-heating event. The formation of rims on lunar soils is complex and involves several processes whose effects may be superimposed.From this study, it is shown that one process does not dominate and that the relative importance of vapor-deposition is comparable to radiation-damage in the formation of rims on lunar silicate grains. The presence of rims on lunar soil grains, particularly those with nanometer-sized Fe metal inclusions, may have a major influence on the optical and magnetic properties of lunar soils.

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