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.