Mawrth Vallis sourrounded by interesting terrain
Starting on the old and cratered “Highland” terrain, the 25 km wide impact crater on the left side (south) of the image shows a central pit and a part of its northern wall is collapsed. Central pit craters are impact craters, often observed on ice-rich planets and moons. The raised rims around the central pit is strongly suggestive of explosive excavation by steam explosion. Further to the right (north), large patches of the light-toned and clay-rich materials can be found. At closer look, they can also be found within crater walls, e.g. the smaller crater in the lower portion of the image. The dark, volcanic cap rock unit is also present in patches, often strongly eroded. Further to the north, the terrain steeply drops into the “Lowland” of Cryse Planitia. Two interconnected old and eroded impact crater walls can still stand out in the plain. The larger one measures roughly 75 km, the smaller one at the upper image border about 35 km in diameter. Further north, a field of numerous knobs and mesas can be spotted the larger mesas measure up to 3 km and they appear to be remnants of the former, now eroded “Highland” materials. Finally, in the top right corner of the image, a portion of a fluidized (or rampart) ejecta blanket can be found. These result from an impact into a surface that contains water or ice. According to the prevailing model, the water was released by the impact together with tons of rock and debris and the ejecta flowed like mud.