Greeley Impact Crater is located in Noachis Terra, an area of the southern highlands between the Argyre and Hellas Planitia impact basins and, with a diameter of 427 kilometres, is one of the largest impact craters on Mars. This ancient crater, which has already been heavily eroded and filled with sediment, is difficult to make out against the Martian landscape due to its relatively shallow depth of only 1.5 kilometres – indeed, the crater rim has disappeared altogether in places. An astronaut standing in the middle of the crater would not be able to see the crater rim on the horizon at all due to the curvature of Mars, which is greater than Earth’s. The crater outline is most visible on the colour-coded digital terrain model.