Courtesy of NASA/JPL/Malin Space Science Systems.

Comments:
The bottom right corner of this image shows what appears to be a dam - Zorgon

Courtesy of NASA/JPL/Malin Space Science Systems. Full Image Without Notes  -  With Notes

Figure A: This set of images shows a comparison of the gully site as it appeared on Dec. 22, 2001 (left), with a mosaic of two images acquired after the change occurred (the two images are from Aug. 26, 2005, and Sept. 25, 2005). Sunlight illuminates each scene from the northwest (top left). The 150-meter scale bar represents 164 yards.

In June 2000, we reported the discovery, using the Mars Global Surveyor's Mars Orbiter Camera, of very youthful-looking gullies found on slopes at middle and high latitudes on Mars. Since that time, tens of thousands of gullies have been imaged by all of the Mars orbiting spacecraft: Mars Global Surveyor, Mars Odyssey, Mars Express and Mars Reconnaissance Orbiter.

During the years since the original June 2000 report, the Mars Global Surveyor's camera was used to test the hypothesis that the gullies may be so young that some of them could still be active today. The test was very simple: re-image gullies previously seen by the camera and see if anything has changed.

In two cases, something changed. One of those cases is presented here. A gully on the wall of an unnamed crater in Terra Sirenum, at 36.6 degrees south, 161.8 degrees west, was initially imaged by the camera on Dec. 22, 2001 (Figure A, left). It showed nothing noteworthy at the location where a change would later be observed, but a group of nearby gullies exhibited an unusual patch of light-toned material. As part of our routine campaign to re-image gully sites using the camera, another image of this location was acquired on April 24, 2005. A new light-toned deposit had appeared in what was otherwise a nondescript gully (Figure A, right). This deposit was imaged again by the camera on Aug. 26, 2005, at a time when the sun angle and season were the same as in the original December 2001 image, to confirm that indeed the light-toned feature was something new, not just a trick of differing lighting conditions. In August 2005, the feature was still present.

Courtesy of NASA/JPL/Malin Space Science Systems Full Size Image w/ Notes Left Side  -  Right Side Full Size Image w/o Notes Left Side  -  Right Side

Figure B: This is a mosaic of images that cover the entire unnamed crater in Terra Sirenum. The location of the light-toned gully deposits, old and new, is indicated. This is a mosaic of images acquired by the camera in 2005 and 2006. The 500-meter scale bar equals approximately 547 yards. Figure C: This image shows an enlargement of a portion of another image from August 2005, showing details of the new, light-toned gully deposit. The new material covers the entire gully floor, from the point at which the gully emerged from beneath a mantled slope, down to the spot at which the channel meets the crater floor. At this break in slope, the gully material, as it was emplaced, spread out into five or six different fingers (this is called a "digitate" termination as in finger digits). The 75-meter scale bar represents a distance of about 82 yards.

The light tone of the new gully deposit, and that of the older, neighboring gullies, is intriguing. We cannot know from these images whether the light tone indicates that ice is still present in and on the surface of the deposit. Indeed, ice may not be likely: under present conditions on the surface of Mars, ice would be expected to have sublimed, or vaporized, away fairly shortly after the new deposit formed. However, the light-toned material could be frost that forms and re-forms frequently as trapped water-ice sublimes and "exhales" from within the deposit. Alternatively, the light-tone may result if the deposit consists of significantly finer grains (for example, fine silt) than the surrounding surfaces, or if the deposit's surface is covered with minerals such as salts formed as water evaporated from the material.

Courtesy of NASA/JPL/Malin Space Science Systems.

Figure D: To confirm that the new, light-toned gully deposit is not just a trick of changing illumination conditions as the sun rises to different levels in the sky each season, the Mars Orbiter Camera team repeatedly imaged this site throughout 2005 and 2006. Four examples are shown here, acquired in April 2005, August 2005, February 2006 and April 2006. The "i=" indicates solar-incidence angle, or the height of the sun in the local sky, relative to a case where the sun would be directly overhead (i=0 degrees). Thus, the higher the incidence angle, the lower the sun would appear in the sky to an observer on the ground

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

Courtesy of NASA/JPL/Malin Space Science Systems. Full Image Without Notes  -  With Notes

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.

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 (click here: PIA09027). 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.
 
 
 

Courtesy of NASA/JPL/Malin Space Science Systems. Full Image B (left) - C (center) w/o notes  -  w/notes - D(right)

Figure B: 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 C: The third 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 D: The fourth 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

Credit: NASA/JPL/Malin Space Science Systems 

UH Astrobiology Team Studies Water and Life in the Universe