13 December 2004
This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows fine details among mid-latitude gullies formed on the walls of a large pit within a filled meteor impact crater in the Noachis Terra region of Mars. Like the gullies originally described in June 2000, these may have formed by the seepage of groundwater. Other scientists have speculated that, elsewhere on Mars, similar gullies might form by melting of ice or snow, by liquid or gaseous carbon dioxide, or dry mass movement (landsliding) processes. The many fine tributaries in the Noachis pit crater area shown here lend support to the hypothesis that a liquid with the physical properties of water was involved. This image is located near 47.8°S, 354.9°W, and covers an area approximately 3 km (1.9 mi) wide. The scene is illuminated by sunlight from the upper left.