Small rampart craters in an equatorial region on Mars: Implications for near-surface water or ice

Abstract

Small onset diameters (1 km) of rampart craters were identified in High Resolution Stereo Camera (HRSC) imagery in the equatorial region of the Valles Marineris plateaus. This is in contrast to previous global studies based on Viking imagery, which showed onset diameters in the range of 4 km to 7 km in equatorial regions. The observed small rampart craters show morphologically eroded ejecta blankets. This indicates a formation in the early Martian history, when erosion rates were higher. Volatile rich target material might have been available shortly after the formation of the Hesperian-aged plateaus surrounding Valles Marineris, and this is in agreement with the reported Hesperian fluvial activity in this region. The lack of fresh small rampart craters indicates a lowering of the ground ice table with time.