Figure: New Gully Deposit in a Crater in the Centauri Montes Region (Larger View).

Two Martian southern mid-latitude craters have new light-toned deposits that formed in gully settings during the course of the Mars Global Surveyor mission. Images from the Mars Orbiter Camera documented one case in an unnamed crater in Terra Sirenum, described here. The second case, in an unnamed crater in the Centauri Montes region, east of the Hellas Basin, is described here.

The new gully deposit in an unnamed crater in the Centauri Montes region is located near 38.7 degrees south latitude, 263.3 degrees west longitude. Like the new gully deposit in Terra Sirenum, this one has a light tone relative to its surroundings. It is on an equator-facing slope on which numerous narrow gully channels occur. As this slope is always in sunlight during the afternoons when Mars Global Surveyor passes overhead, the gullies always appear somewhat "washed out," just as craters on a full Moon do when viewed from Earth with a telescope.

The new, light-toned flow was first noticed by the Mars Orbiter Camera science operations team in an image acquired on Sept. 10, 2005. Re-examination of other images of this crater showed that the new deposit had actually been present on Feb. 21, 2004, when the distal (down-slope) end of the deposit was captured in other images. In February 2004, the deposit had gone unnoticed because only a small portion of it was imaged. This location was first imaged by the Mars Orbiter Camera on Aug. 30, 1999. The deposit was not present at that time. Thus, it formed between Aug. 30, 1999 and Feb. 21, 2004.

Roughly 20 percent brighter than the surface as it appeared before the flow occurred, the new deposit exhibits characteristics consistent with transport and deposition of a fluid that behaved like liquid water and likely transported some fine-grained sediment along with it. The distal end of the flow broke into several branches, or digits, and the material diverted and flowed around low obstacles. As with the example in Terra Sirenum, the depth of the flow is too thin to be measured in 1.5-meter-per-pixel images, so a very small volume of liquid and sediment was involved. While the material flowed and easily budded into several branches, it also must have moved slow enough to not topple over some of the low obstacles in its path.

This figure is a mosaic of several Mars Global Surveyor images, colorized using a table derived from Mars Reconnaissance Orbiter camera color data and overlain on a sub-frame of a Mars Odyssey Thermal Emission Imaging System image (for more figures, see here).

The new light-toned flow, by itself, does not prove that liquid water was involved in its genesis. However, this observation and the similar light-toned flow in Terra Sirenum together show that some gully sites are indeed changing today, providing tantalizing evidence there might be sources of liquid water beneath the surface of Mars right now. In both cases, these new flows may be indicating the locations of aquifers (subsurface rocks saturated with water) that could be detected by orbiting, ground-penetrating radar systems such as the Mars Express Mars Advanced Radar for Subsurface and Ionosphere Sounding or the Mars Reconnaissance Orbiter's Mars Shallow Subsurface Radar.

The Mars Global Surveyor mission is managed for NASA's Office of Space Science, Washington, by NASA's Jet Propulsion Laboratory, Pasadena, Calif., a division of the California Institute of Technology, also in Pasadena. Lockheed Martin Space Systems, Denver, developed and operates the spacecraft. Malin Space Science Systems, San Diego, Calif., built and operates the Mars Orbiter Camera.

For more information about images from the Mars Orbiter Camera, see http://www.msss.com/mgs/moc/index.html.

Credit: NASA/JPL/Malin Space Science Systems

http://www.nasa.gov/mission_pages/mars/images/pia09028.html