Gullies on Gorgonum Chaos Mesas
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Gullies on Gorgonum Chaos Mesas

March 30, 2007

This image shows part of Gorgonum Chaos, a large cluster of chaotic terrain found in the southern hemisphere.

Many regions of chaotic terrain are found at the head of large outflow channels that were scoured by ancient floods. Gorgonum Chaos is one region that is not associated with an outflow channel.

Chaotic terrain can form when subsurface volatiles (such as water) are catastrophically released and the overlying surface collapses. It is not known whether isolated chaotic terrain—such as that shown in this image—formed in the same way that the chaotic terrain near the outflow channels did. Wind erosion might play a role in their formation.

Gorgonum Chaos is an especially interesting area because gullies thought to have been eroded by liquid water are located on its mesas (see subimage (3.4 MB, 1800 x 664); scene is approximately 4 km across). The gullies have a wide range of orientations and many appear to emanate from a distinct layer in the mesas (see subimage).

It is not known why gullies form on one slope rather than another, but insolation (amount of sunlight received), availability of water, and regional slope are possible contributing factors.

Observation Geometry

Image PSP_001948_1425 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 26-Dec-2006. The complete image is centered at -37.1 degrees latitude, 189.5 degrees East longitude. The range to the target site was 254.9 km (159.3 miles). At this distance the image scale is 25.5 cm/pixel (with 1 x 1 binning) so objects ~76 cm across are resolved.

The image shown here has been map-projected to 25 cm/pixel and north is up. The image was taken at a local Mars time of 03:43 PM and the scene is illuminated from the west with a solar incidence angle of 70 degrees, thus the sun was about 20 degrees above the horizon. At a solar longitude of 156.4 degrees, the season on Mars is Northern Summer.

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