DETECTION OF ATOMIC DEUTERIUM IN THE UPPER-ATMOSPHERE OF MARS

Citation
Va. Krasnopolsky et al., DETECTION OF ATOMIC DEUTERIUM IN THE UPPER-ATMOSPHERE OF MARS, Science, 280(5369), 1998, pp. 1576-1580
Citations number
45
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Multidisciplinary Sciences
Journal title
ISSN journal
0036-8075
Volume
280
Issue
5369
Year of publication
1998
Pages
1576 - 1580
Database
ISI
SICI code
0036-8075(1998)280:5369<1576:DOADIT>2.0.ZU;2-X
Abstract
High-resolution spectroscopy of Mars' atmosphere with the Hubble Space Telescope revealed the deuterium Lyman alpha line at an intensity of 23 +/- 6 rayleighs. This measured intensity corresponds to HD/H-2 = 1. 5 +/- 0.6 x 10(-4), which is smaller by a factor of 11 than HDO/H2O. T his indicates that fractionation of HD/H-2 relative to that of HDO/H2O is not kinetically controlled by the rates of formation and destructi on of H-2 and HD but is thermodynamically controlled by the isotope ex change HD + H2O <-> HDO + H-2. Molecular hydrogen is strongly depleted in deuterium relative to water on Mars because of the very long lifet ime of H-2 (1200 years). The derived isotope fractionation corresponds to an estimate of a planetwide reservoir of water ice about 5 meters thick that is exchangeable with the atmosphere.