Layered Deposits in Terby
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Layered Deposits in Terby

January 29, 2007

Terby Crater is a large (diameter ~165 km), Noachian-aged crater located on the northern rim of the Hellas impact basin (28ºS, 74.1ºE).

Terby hosts a very impressive sequence of predominantly light-toned layered deposits, up to 2.5 km thick that are banked along its northern rim and extend toward the center of the crater.

HiRISE image PSP_001662_1520 shows this stack of layered rocks as they are exposed westward facing scarp. The layered sequence consists of many beds that are repetitive, relatively horizontal and laterally continuous on a kilometer scale. Many beds are strongly jointed and fractured and exhibit evidence of small-scale wind scour.

The light-toned layers are typically at least partially covered with dark mantling material that obscures the layers as well as debris and numerous, meter-scale boulders that have cascaded down slope. The processes responsible for formation of these layers remain a mystery, but could include deposition in water, by the wind, or even volcanic activity.

Observation Geometry

Image PSP_001662_1520 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 03-Dec-2006. The complete image is centered at -27.6 degrees latitude, 74.2 degrees East longitude. The range to the target site was 258.2 km (161.4 miles). At this distance the image scale is 25.8 cm/pixel (with x binning) so objects ~77 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 03:40 PM and the scene is illuminated from the west with a solar incidence angle of 68 degrees, thus the sun was about 22 degrees above the horizon. At a solar longitude of 144.9 degrees, the season on Mars is Northern Summer.

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