Solar System nebular phase

It is difficult to decipher early solar-system history from observations of the planets themselves, since most of their earliest records have been obliterated by subsequent processing. However, the meteorites, mostly derived from asteroids, have remained largely unchanged since their constituent minerals formed in the presence of the nebular gas, and thus provide the best information on early chemical and physical processes, such as evaporation and condensation, or chemical exchange between gas and condensed phases. 

In contrast to Earth, Martian Xe apparently did not evolve from a U-Xe progenitor. Modeling derivation of primordial Xe composition on Mars is based on analyses of atmospheric gases trapped in glassy phases of SNC meteorites (Swindle 2002, this volume). Present ambiguities in this data base are such that two different solar-system Xe compositions, carbonaceous chondrite (Cl)-Xe and SW-Xe, are possible candidates—but not U-Xe. Exclusion of U-Xe as the dominant primordial atmospheric inventory on Mars, despite the implication of the terrestrial modeling that it was a major component of the nebular gas phase, requires that accretion of Cl- or SW-Xe-rich materials from sources more localized in space or time has overwhelmed the isotopic signature of its presence. 

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