Variability of Mars' north polar water ice cap. Part II: Analysis of Viking IRTM and MAWD data

We have examined Viking Orbiter albedo, thermal, and atmospheric water vapor data acquired during Mars' northern summer season and compared these results with the imaging results of D. S. Bass, K. E. Herkenhoff, and D. A. Paige (2000, Icarus 144, 382-396). The Viking thermal mapper data show an increase in the albedo of the entire north water ice cap, consistent with imaging data results. We find a strong correlation between polar cap surface temperature and atmospheric water vapor, but we note that the atmospheric water vapor data do not increase dramatically until the cap center temperature exceeds 200 K. The Viking Infrared Thermal Mapper data support the conclusion that cold trapping is the correct explanation for the observed late summer brightening of the residual water ice cap. We suggest that the retreating seasonal carbon dioxide cap takes the water with it and not until the receding cold trap reaches the cap center is the bulk of the water released into the atmosphere. This process, plus the deposition of fresh ice onto the cap later in the summer season, will tend to close the north polar cap's annual water cycle.