HIGH-RESOLUTION SUBSURFACE WATER ICE DISTRIBUTIONS ON MARS DERIVED FROM THERMAL INFRARED TEMPERATURE MEASUREMENTS

The presence of water ice in the shallow subsurface (<1-2 m depths) at Martian high latitudes has been principally supported by theoretical models and by the presence of large concentrations of hydrogen detected by the Gamma Ray Spectrometer (GRS) suite of instruments on the Mars Odyssey (M01) spacecraft. The models and measurements are consistent with a water-ice table that generally increases in depth with decreasing latitude. Measurements have been limited to the several hundred kilometer footprint of the GRS suite, however, preventing the observations from documenting more detailed water ice distributions. It is also possible to detect and determine the depth of Martian permafrost layer by measuring the temperature of the Martian surface at different seasons with the Thermal Emission Imaging System (THEMIS) on M01 and the Thermal Emission Spectrometer (TES) on the Mars Global Surveyor spacecraft. These observations show significant regional and local water ice depth variability at <1-10 km scales that appears to be controlled by the thermophysical properties of the surface layer. The high resolution THEMIS measurements show that the depth to the water-ice table is highly variable within the potential Phoenix spacecraft landing ellipses and is likely to be variable at scales that may be sampled by the spacecraft. Because of the relatively high spatial resolution of the infrared temperature measurements, it is possible they may provide a useful link between the Phoenix lander observations and the regional scale GRS suite of measurements. The presence of water ice where it follows the depth of stability under current climatic conditions implies an active Martian water cycle that responds to orbit driven climate cycles.