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This is one of the strangest looking craters ever found on Mars, and this platypus-tail-shaped depression, called Orcus Patera, is an enigma. The term ‘patera’ is used for complex or irregularly shaped volcanic craters, but planetary scientists aren’t sure if this landform is volcanic in origin. Orcus Patera lies between the volcanoes of Elysium Mons and Olympus Mons, but its formation remains a mystery. This is the latest image of the object, taken by ESA’s Mars Express.
It could be an impact crater that originally was round, but then subsequently deformed by compressional forces. Or, it could have formed from two craters next to each where the adjoining rims eroded. However, the most likely explanation is that it was made in an oblique impact, when a small body struck the surface at a very shallow angle.
It is 380 km long by by 140 km wide, and has a rim that rises up to 1,800 meters above the surrounding plains, while the floor of the depression lies 400–600 m below the surroundings. The floor of the depression is unusually smooth.
The image above was created using a Digital Terrain Model (DTM) obtained from the High Resolution Stereo Camera on ESA’s Mars Express spacecraft. Elevation data from the DTM are color-coded: purple indicates the lowest-lying regions, and beige the higher elevations. The scale is in meters.