The Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) captured two examples of gullies on crater walls in which a change occurred between 1999 and 2005. In each case, one in Terra Sirenum (see New Gully Deposit in a Crater in Terra Sirenum), the other in the Centauri Montes (see New Gully Deposit in a Crater in the Centauri Montes Region), new light-toned material was deposited during the MGS mission. These new light-toned deposits may be indicators that water flowed at these two gully sites during the past few years. Naturally, a question arises: Are there other gullies at which similar light-toned deposits have formed?
To answer the question, the MOC team at Malin Space Science Systems (MSSS) reviewed every MOC image ever taken of a martian gully. Most of the gullies occur at middle latitudes in both the northern and southern hemispheres. This re-examination turned up several good examples of other light-toned materials deposited in gullies. However, in none of these cases is there a "before" image, with no light-toned material, followed by an "after" image in which new light-toned material had appeared. Thus, one cannot know how long ago these other light-toned deposits formed. However, these are excellent candidates for future monitoring with orbiter cameras that have sufficient spatial resolution to look for new light-toned deposits, should they form during the coming years. Shown here are three of the best examples the MOC team identified.
This image shows several gullies with light-toned material on their floors and deposited in their aprons. This area is located on the northeast wall of Hale Crater near 35.5Â°S, 35.4Â°W. The picture is a mosaic of MOC images R07-02277 (acquired 31 July 2003), R13-01791 (acquired 11 January 2004), and S16-01780 (acquired 21 March 2006). The 500 meter scale bar is 547 yards long.