Chryse Planitia is a smooth circular plain in the northern equatorial region of Mars close to the Tharsis region. It is 1600 km in diameter and with a floor 2.5 km below the average planetary surface altitude, and is thought to be an ancient impact basin; it has has several features in common with lunar maria, such as wrinkle ridges. The density of impact craters in the 100m to 2000m range is close to half the average for lunar maria.

Chryse Planitia shows evidence of water erosion in the past, and is the bottom end for many outflow channels from the southern highlands as well as from Valles Marineris and the flanks of the Tharsis bulge. It has been theorized that the Chryse basin may have contained a large lake or an ocean during the Hesperian or early Amazonian periods since all of the large outflow channels entering it end at the same elevation, at which some surface features suggest an ancient shoreline may be present. Chryse basin opens into the north polar basin, so if an ocean was present Chryse would have been a large bay.

The Viking 1 landed in Chryse Planitia, but its landing site was not near the outflow channels and no fluvial features were visible; the terrain at that point appeared primarily volcanic in origin. The Mars Pathfinder landed in Ares Vallis , the end of one of the outflow channels emptying into Chryse.

External links

• Outflow Channels May Make a Case for a Bygone Ocean on Mars