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Escape of H and D from Mars' Atmosphere and the Evolution of its Crustal Water ReservoirsThe evolution of water on Mars involves preferential escape of hydrogen over deuterium, producing its deuterium rich atmosphere with a D/H ratio 5.2 times that of terrestrial water. In the past decade, several estimates have been made of the magnitudes of current and ancient crustal water reservoirs on Mars that freely exchange with its atmosphere. Some of the differences in the magnitudes of the reservoirs are influenced by differences in the following basic parameters: composition of H, D, H2 and HD at the exobase; thermal history of the atmosphere; escape mechanisms; and the D/H ratio of earlier epochs as inferred from meteorites. The dominant escape mechanism used in the estimates is Jeans escape. However, the Jeans escape flux is enhanced considerably when atmospheric winds and rotation are applied at the exobase . This constraint is of particular importance because the enhancement of the D escape flux can be an order of magnitude greater than the enhancement of the H escape flux. This preferential enhancement of the D escape flux over that of H means that a great deal more H must escape (than in the case without winds and rotation) to attain the same D/H ratio in the today's atmosphere. Another new constraint on reservoir magnitudes comes from the recent interpretation of Martian meteorite data, which suggests that the D/H ratio was 2 times that of terrestrial water at the end of the heavy bombardment period (1). These two constraints together lead to larger current and ancient crustal water reservoirs. Applying Rayleigh fractionation, new estimates of the sizes of the water reservoirs are made using the above constraints along with plausible values for hydrogen and deuterium densities, temperatures, wind speeds and rotation rates at the exobase.
Document ID
20020028891
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
Hartle, Richard E.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Einaudi, Franco
Date Acquired
August 20, 2013
Publication Date
January 1, 2001
Subject Category
Lunar And Planetary Science And Exploration
Meeting Information
Meeting: 2001 Fall AGU Meeting
Location: San Francisco, CA
Country: United States
Start Date: December 10, 2001
End Date: December 14, 2001
Sponsors: American Geophysical Union
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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