Evidence for Non-Equilibrium Distributions of Water-Equivalent Hydrogen Deposits near the Surface of Mars

Details Evidence for Non-Equilibrium Distributions of Water-Equivalent Hydrogen Deposits near the Surface of Mars Evidence for Non-Equilibrium Distributions of Water-Equivalent Hydrogen Deposits near the Surface of Mars

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p32c..02f&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #P32C-02

Physics

5416 Glaciation, 5462 Polar Regions, 6225 Mars

Scientific paper

Spatial distributions of water-equivalent hydrogen deposits within 45 degrees of the equator inferred from epithermal and fast neutron data, measured using the Neutron Spectrometer aboard Mars Odyssey, were compared with estimates of the annual-mean water-ice stability of surface soils, to search for evidence of recent climate change on Mars. A calculated stability factor given by the ratio of elevation-dependent near-surface atmospheric humidity to the annual-mean frost-point humidity for the soil, was used for this purpose. These estimates of potential distributions of subsurface ground-ice used new high-resolution maps of thermal inertia, albedo, and elevation from Mars Global Surveyor [Mellon et al., Icarus, submitted, 2003]. We found that all observed water-equivalent hydrogen deposits within about 40 degrees of the equator should be unstable. Furthermore, the model calculations show that although all such deposits are unstable, there should be a bias toward stability north of the equator. This bias is also not consistent with the neutron data. When these facts are coupled with the maximum observed water-equivalent hydrogen abundance of 13 percent by mass in a 10-degree diameter arc centered on 5 degrees latitude and +25 degrees east longitude, we are led to conclude that not only must atmospheric condition have been different in the recent past than is currently observed, but that our assumptions about the physical structure of subsurface soils near the equator must be different than we presently model.

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