Astronomy

Noble Gases and Martian Water

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Science  25 Feb 2000:
Vol. 287, Issue 5457, pp. 1365
DOI: 10.1126/science.287.5457.1365a

Nakhlites, one of the three classes of meteorites that originated from Mars, have a distinctive noble gas signature that may be related to isotopic fractionation that occurred during water-rock interactions on the martian surface. Studies of these meteorites may provide important clues concerning Mars paleoenvironment.

Swindle et al. analyzed argon, krypton, and xenon concentrations in the nakhlite Lafayette, which contains the highest concentration of hydrous mineral phases of any martian meteorite, and focused primarily on iddingsite, which is a mixture of clay minerals, iron oxides, and ferrihydrides. The Kr and Xe are enriched in the iddingsite relative to the other mineral phases in the sample, suggesting that the iddingsite is a potentially important carrier of the noble gas signature of the martian hydrosphere or atmosphere or both. The Xe fraction is isotopically distinct from terrestrial Xe and therefore martian in origin, and may represent trapped martian atmosphere from a shock process, Xe trapped in the polar ice in clathrates, or a time-varying Xe component of the atmosphere. The authors derived an upper limit of 670 ± 91 million years for the age of the formation of the iddingsite from K-Ar isotopic systematics. This finding suggests that liquid water may have been available on Mars more recently than suggested by martian surface morphology.—LR

Meteorit. Planet. Sci. 35, 107 (2000).

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