Rampart crater
A rampart crater has ejecta that flowed outwards like mud, ending in a raised ridge, common on Mars.
A rampart crater is surrounded by ejecta that seems to have flowed across the ground like a mudflow, ending in a low ridge, or rampart. The ejecta forms lobes or layers, quite different from the scattered rays and blocks around most lunar craters.
Rampart craters are common on Mars, where they are also called layered ejecta craters. Many scientists think they form when an impact strikes ground containing ice or water. The heat of the impact melts the ice, turning the ejected material into a slurry that flows outwards. Others suggest that the thin Martian atmosphere also shapes the ejecta.
The sizes and locations of rampart craters have been used to map where ice may lie under the Martian surface, which matters for understanding Mars's past climate and for future explorers who might need water. Similar craters have been found on Jupiter's icy moon Ganymede and on Venus, where the thick atmosphere affects how ejecta spreads.
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