Figure: Light-toned gully materials Hale Crater.
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 35.5 oS, 35.4 oW. The picture is a mosaic of 3 MOC images acquired on 31 July 2003, 11 January 2004 and 21 March 2006.
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 is one of the best examples the MOC team identified.
Accompanying captioned releases regarding gullies on Mars:
Credit: NASA/JPL/Malin Space Science Systems
http://www.msss.com/mars_images/moc/2006/12/06/gullies/other_examples/index.html