SHALLOW VOLATILE LAYER AT CHRYSE-PLANITIA, MARS

We have investigated size distribution of rampart craters in the east edge of Chryse Planitia on Mars by Viking high resolution images. Clea r existence of the onset diameter of rampart crater, which defines the minimum size of the rampart crater, has been recognized. If this diam eter corresponds to the depth to the top of the volatile layer, the co nverted depth ranges from similar to 20 m to 60 m. These values are sy stematically shallower than the previous estimates (Kuzmin, 1988). Mar tian volatile layer is thought as a main reservoir of the ancient fluv ial processes and atmospheric water vapor. This shallow volatile layer gives us information of the inventory of Martian water and conditions of cryosphere.