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P.B. James (Univ. Toledo), B.A. Cantor (MSSS)
One of the significant results of the Viking Mission was that the residual north polar cap on Mars, the cap "remnant" that remains throughout summer, is composed of water ice [Kieffer er al., Science 194, 1976]. The reservoir of water in the residual north cap is still the largest that has been firmly established, and sublimation of water from the cap is an important source of water vapor in the Martian atmosphere. Net depletion or accumulation of water in the cap from year to year reflects transport to other reservoirs such as the regolith and to deposits in the seasonal caps.
The MOC wide-angle cameras on Mars Global Surveyor have observed the residual north cap for two consecutive Martian years. We observed significant differences in the cap configurations in the two years. In particular, the cap was larger in 1999 than in 2001, with the cap in the latter year closely resembling that observed during the Mariner 9 mission [Cantor et al., J. Geophys. Res. (submitted)] despite the fact that the cap regression in the latter year was unexceptional [James and Cantor, Icarus (in press)].
This research was supported by a MGS Team Data Analysis grant from the Mars Exploration Directorate and by a grant from the Mars Data Analysis Program.