Layers and Dark Debris
This HiRISE sub-image shows layering in a light-toned deposit in Melas Chasma.
The layers are sedimentary in origin, but there are many processes that could have deposited them, such as volcanic airfall from explosive eruptions, dust-size particles settling out of the atmosphere due to cyclic changes, and deposition in standing bodies of water.
By looking at the slopes in the layers and how the layers intersect each other, scientists can rule out various origins. A darker material can be seen covering much of the layered deposit. Some of this dark material is loose and can be seen accumulating as debris aprons at the base of steep slopes. Other dark material appears indurated and has been eroded by the wind to form etched edges with topographic expressions.
The lack of impact craters on the layered deposit indicates that it is a relatively young deposit, or the craters have been removed by the wind, or the deposit was quickly buried and is now being exhumed.
Image PSP_002419_1675 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 31-Jan-2007. The complete image is centered at -11.4 degrees latitude, 287.6 degrees East longitude. The range to the target site was 263.5 km (164.7 miles). At this distance the image scale is 26.4 cm/pixel (with 1 x 1 binning) so objects ~79 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 57 degrees, thus the sun was about 33 degrees above the horizon. At a solar longitude of 176.2 degrees, the season on Mars is Northern Summer.