A 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. Clear existence of the onset diameter of rampart crater, which defines the minimum size of the rampart crater, has been recognized. If this diameter corresponds to the depth to the top of the volatile layer, the converted depth ranges from ∼20 m to 60 m. These values are systematically shallower than the previous estimates (Kuzmin, 1988). Martian volatile layer is thought as a main reservoir of the ancient fluvial processes and atmospheric water vapor. This shallow volatile layer gives us information of the inventory of Martian water and conditions of cryosphere.