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Mars Global Surveyor
Mars Orbiter Camera

8 Years at Mars #3: Rolling Stones Make New Boulder Tracks

MGS MOC Release No. MOC2-1222, 20 September 2005

MOC2-1222a: Context, north is up
Context view from MOC wide angle images, showing location of crater in which boulder tracks occur.
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NASA/JPL/Malin Space Science Systems 		MOC2-1222b: New boulder tracks on slope; north is down
Two MOC images, one from 14 November 2003, the other from 4 December 2004, showing boulder tracks on crater wall; the December 2004 image shows that more than a dozen new tracks formed within the previous year.
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NASA/JPL/Malin Space Science Systems

When a boulder rolls down a dusty slope, it can leave behind a trail of depressions. Usually known as boulder tracks, these features have been documented and studied on Earth, the Moon, and Mars. Geologists studying the Moon and Mars can use these tracks to learn about the physical properties of the fine-grained debris encountered by the boulder as it rolled down the slope.

Because of the high resolution (0.5 to 12 meters, 1.6 to 39 feet, per pixel) capability of the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC), dozens of boulder track sites have been identified on the red planet (links to some examples are provided below, among the reference materials).

A MOC image of one set of boulder tracks in a south mid-latitude crater (located near 35.8°S, 158.4°W) was obtained in November 2003. The first picture (MOC2-1222a, above) shows a mosaic of MOC wide angle Geodesy Campaign images acquired in May 1999; the white box indicates the location of the higher-resolution views in the second figure (MOC2-1222b). The second picture shows the mid-November 2003 MOC image, side-by-side with a later MOC image obtained in early December 2004.

The second image, from December 2004, shows that more than a dozen new boulder tracks formed on the crater wall during the approximately 1 Earth year interval. Mars is an active planet, with geologic changes occurring -- at some scale -- every day. In this case, sometime between November 2003 and December 2004, a suite of boulders became dislodged from the crater wall and rolled and perhaps bounced their way to the crater floor.

Why the new boulders slid down the slope is unknown. This is the product of a mass movement (landsliding) process. That is, gravity is the main culprit. Whether the boulder motion was triggered by something -- a seismic event ("Marsquake") or strong winds -- is not known. Also unknown is whether all of the new boulder tracks formed at the same time, in response to a single event, or rolled downhill one at a time over the nearly 13-month period.

Reference Material:

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Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, California. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, California and Denver, Colorado.