Cerberus' River

The prominent trough in this sub-image (of HiRISE image TRA_000827_1875_IRB ) is a segment of the Cerberus Fossae rift system. In geological terminology the trough is known as a graben, or down-dropped region bounded by faults. In this location the graben is about 300 m wide and 90 m deep. Bright, dust-covered, cratered plains surround the graben, and darker sediments blanket much of its floor. Dunes that vary in size and spacing occur within the darker sediments, and their shapes suggest that the wind typically blows from east to west. Light-toned, angular boulders pepper the darker sediments. They have broken away from the rocky walls of the graben and tumbled downhill. Over time this mass wasting has caused the cliffs to retreat, widening the trough. The somewhat lighter patches of cratered terrain on the graben floor were once level with the surrounding plains, but have since been lowered by faulting. Over time they may become obscured or buried by the darker sediments. High-standing ridgesÑremnants of the former surfaceÑcast jagged shadows on the floor of the graben that reveal the rugged nature of the landscape in this region of Mars.
Image TRA_000827_1875 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on September 29, 2006. The complete image is shown below, centered at 7.4 degrees latitude, 168.5 degrees East longitude. The range to the target site was 275 km (171 miles). At this distance the image scale is 55 cm/pixel (with 2 x 2 binning) so objects ~165 cm across are resolved. The image shown below has been map-projected to 50 cm/pixel and north is up. The image was taken at a local Mars time of 3:26 PM and the scene is illuminated from the west with a solar incidence angle of 51.9 degrees, thus the sun was about 38.1 degrees above the horizon. At a solar longitude of 113.7 degrees, the season on Mars is Northern Summer / Southern Winter.