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 in an accompanying release (see PIA09027 or MOC2-1618). The second case, in an unnamed crater in the Centauri Montes region, east of the Hellas Basin, is described here.
Gullies were first described by Mars Orbiter Camera scientists in June 2000, and many examples were presented in our June 2000 web releases and in a paper published in the journal Science. Additional examples of these middle and high-latitude landforms can be seen among the other more than 1,600 web releases.
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 (1.7-yard-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 picture is a colorized view of the light-toned gully deposit, draped over a topographic image derived from Mars Global Surveyor's Mars Orbiter Laser Altimeter data. The color comes from a table derived from the colors of Mars as seen by the Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment.
Figure A: This figure shows the southeast wall of the unnamed crater in the Centauri Montes region, as it appeared in August 1999, and later in September 2005. No light-toned deposit was present in August 1999, but appeared by February 2004. The 300-meter scale bar represents 328 yards.
Figure B: The second 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. The 1-kilometer scale bar represents about 0.62 miles.
Figure C: The third figure is a colorized view of the light-toned gully deposit as viewed from an oblique perspective, draped over topography derived from Mars Global Surveyor's Mars Orbiter Laser Altimeter data. The color comes from a table derived from the colors of Mars as seen by the Mars Reconnaissance Orbiter camera.
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.