Time Variation of the North Polar Seasonal Frost Cap of Mars

Details Time Variation of the North Polar Seasonal Frost Cap of Mars Time Variation of the North Polar Seasonal Frost Cap of Mars

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p11b..03f&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #P11B-03

Physics

5405 Atmospheres: Composition And Chemistry, 5410 Composition, 5462 Polar Regions, 6225 Mars

Scientific paper

Maps of thermal, epithermal, and fast neutrons covering latitudes northward of +45 degrees were studied to determine the time variation of CO2 frost at northern latitudes during late winter and early spring. Data measured between 18 Feb. and 31 Aug. 2002, were broken into eleven, roughly 7.5 degree intervals of areocentric longitudes, Ls, spanning 321 to 55 degrees. The edge of the CO2 frost cap is seen in thermal neutrons to steadily recede during this interval, revealing subsurface deposits of water-rich soil. Simultaneously, the intensity of thermal neutrons near the pole first increases and then decreases. The thermal flux measured near the pole relative to that measured at the Viking 1 landing site is too low, and those for the epithermal and fast neutrons are too high, to be consistent with fluxes simulated using MCNPX for a roughly meter-thick CO2 layer overlying water-ice rich soil. Agreement of measurements with simulations seems to require a strong neutron absorber in either the overlying atmosphere (such as nitrogen) or the CO2 frost cap (such as dust). Our preferred interpretation is in terms of a nitrogen-rich residual atmosphere that forms in consequence of the freeze-out of CO2 gas from the pre-winter polar atmosphere.

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