A New Look at Mars' Seasonal Water Cycle in the North

Details A New Look at Mars' Seasonal Water Cycle in the North A New Look at Mars' Seasonal Water Cycle in the North

Sep 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996dps....28.0213b&link_type=abstract

American Astronomical Society, DPS meeting #28, #02.13; Bulletin of the American Astronomical Society, Vol. 28, p.1060

Astronomy and Astrophysics

Astronomy

Scientific paper

Mars water cycle variability is likely recorded in polar ice and layered terrains. Previously, we reported an increase in Mars north polar albedo as the northern summer season progresses and believe the albedo increase in Mariner 9 and Viking imaging data is due to the deposition of water ice onto the residual cap and polar layered deposits [Bass et al, 1995]. We present here Viking Infrared Thermal Mapper (IRTM) and Mars Atmospheric Water Detector (MAWD) data of the north polar residual cap as it pertains to Mars seasonal water cycle. Viking IRTM surface temperature (T20) daily average temperature maps and diurnal variations indicate the seasonal CO2 cap uncovers the polar sand sea by Ls = 81.55, but MAWD observations do not show an increase in water vapor at this time. Instead, we find atmospheric water vapor amounts increased substantially only when the minimum diurnal temperature at the cap center reached a nighttime temperature of 200 K. Also, the water vapor peak occurred at the same areocentric solar longitude regardless of the geographic latitude. There is no gradual increase of vapor in the atmosphere as the carbon dioxide cap sublimated, as would be expected if water were sublimating from the surface or regolith directly into the atmosphere. We suggest the immediate source was the retreating polar cap. Finally, MAWD data showed atmospheric water vapor decreasing at the same time IRTM albedo showed cap albedo brightening and T20 data showed a temperature drop, implying water deposited onto the residual cap as the summer progresses. We believe each year observed by Mariner 9 and Viking, water vapor was transported poleward in the spring as the CO2 cap retreated. Immediately after summer solstice, water sublimated into the atmosphere; over the duration of the northern summer season, it gradually accumulated onto the cap and outliers.

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