Computer Science – Performance
Scientific paper
Feb 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000gecoa..64..733e&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 64, Issue 4, pp.733-746
Computer Science
Performance
5
Scientific paper
Variations in the isotopic compositions of oxygen, hydrogen, and carbon in the near-surface environment of Mars are likely influenced by condensation, evaporation, and sublimation of major volatile species (H 2 O, CO 2 ). We present here an experimental study of the fractionations of 18 O/ 16 O and 13 C/ 12 C ratios between CO 2 ice and vapor at conditions relevant to the present near-surface of Mars; these experiments constrain isotopic variations generated by the current Martian CO 2 condensation/sublimation cycle. Oxygen-isotope fractionation between ice and vapor ( ice-vapor = 1000 · ln ([ 18 O ice / 16 O ice ] / [ 18 O vapor / 16 O vapor ]) varies approximately linearly vs. 1/T between temperatures of 150 and 130 K (from 4.2 and 7.5 , respectively). Carbon isotopes are unfractionated ( 13 C ice-vapor 0.2 ) at temperatures 135 K and only modestly fractionated ( 13 C ice-vapor 0.4 ) at temperatures between 135 and 130 K. Martian atmospheric volumes that are residual to high extents of condensation (i.e., at high latitudes during the winter) may vary in 18 O by up to tens of per mil, depending on the scales and mechanisms of ice/vapor interaction and atmospheric mixing. Precise (i.e., per mil level) examination of the Martian atmosphere or ices could be used as a tool for examining the Martian climate; at present such precision is only likely to be had from laboratory study of returned samples or substantial advances in the performance of mass spectrometers on landers and/or orbital spacecraft. Oxygen-isotope fractionations accompanying the CO 2 condensation/sublimation cycle may play a significant role in the oxygen-isotope geochemistry of secondary phases formed in SNC meteorites, in particular as a means of generating 18 O-depleted volatile reservoirs.
Eiler John M.
Kitchen Nami
Rahn Thom A.
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