Characterization of the nighttime low-latitude water ice deposits in the NASA Ames Mars General Circulation Model 2.1 under present-day atmospheric conditions

摘要

This effort advances the exploration of the current Martian water cycle by analyzing the nighttime equatorial water ice deposits in the NASA Ames Mars General Circulation Model (version 2.1). The possibility that the current Martian water cycle plays a role in the generation or maintenance of the longitudinally confined tropical maxima of water-equivalent hydrogen (WEH) in the near-surface regolith is also investigated. Mars Odyssey Orbiter Gamma Ray suite observations indicate that tropical latitudes exhibit longitudinally distinct maxima of the presence of near-surface hydrogen, likely in the form of hydrated minerals, in the Arabia and Tharsis regions. Atmospheric numerical simulations with the NASA Ames Mars General Circulation Model produce an annual water cycle that faithfully reproduces the cycle derived from Mars Global Surveyor Thermal Emission Spectrometer measurements. This simulated water cycle produces maxima of near-surface tropical water condensation at longitudes consistent with the WEH maxima regions, though these maxima are shifted north of the Odyssey Gamma Ray suite WEH regions. While the simulated pattern of near-surface tropical water condensation does exhibit a longitudinal structure consistent with the observed WEH maxima, it is concluded that the current water cycle is not playing a dominant role in the formation or retention of those maxima. Thus, atmospheric involvement in the formation of the WEH-rich regions must occur during past climatic conditions, if at all.