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K and Cl concentrations on the Martian surface determined by the Mars Odyssey Gamma Ray Spectrometer: Implications for bulk halogen abundances in Mars
Author(s) -
Taylor G. Jeffrey,
Boynton William V.,
McLennan Scott M.,
Martel Linda M. V.
Publication year - 2010
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2010gl043528
Subject(s) - mars exploration program , meteorite , chondrite , martian , astrobiology , silicate , martian soil , martian surface , geology , planetesimal , atmosphere of mars , igneous rock , mineralogy , geochemistry , solar system , physics , astronomy
Orbital gamma ray spectrometry shows that the Martian surface has a mean Cl/K ratio of 1.3 ± 0.2, indistinguishable from the ratio in CI chondrites (1.28). Although Cl and K fractionate by magma degassing and aqueous processing, during igneous partial melting both elements are highly incompatible. Thus, if the surface Cl/K reflects the bulk crustal value, then the mantle, hence primitive silicate Mars, also has a roughly CI ratio. Martian meteorite data indicate that Cl/Br is also approximately chondritic, suggesting that elements that condensed in the nebula between ∼1000 K (K and Cl) to ∼500 K (Br) are uniformly depleted in Mars at about 0.6 × CI chondrite concentrations. Mars clearly does not contain 0.6 × CI levels of H 2 O, which would be ∼6 wt%, indicating that Mars was constructed by planetesimals rich in volatile elements, but not in water.