Crater in Terra Cimmeria
This Martian image shows a crater in Terra Cimmeria, approximately 10 km (6 miles) in diameter. The roughly concentric ridges and throughs in this crater's floor are known as "concentric crater fill," and probably result from compression caused by viscous flow of a thick mixture of rocks, soils, and ice inward from the crater's walls.
This and other examples of concentric crater fill occur at high latitudes, where theoretical calculations indicate that ice may exist under the surface, mixed with rocks and soil.
This image's cutout (180 x 560 m, or 200 x 600 yards; 713x2241 pixels, 5 MB) shows a small portion of the crater's north-looking wall; downhill is up, illumination is from the left. In the lower part of the cutout a relatively harder, rocky layer protrudes from the crater's wall; some blocks broke up from it and fell down the slope. Loose soils accumulated behind these blocks (uphill), forming what looks like bright-colored tails. The crater's floor, in the upper part of the cutout, is covered here by elongated dunes. A channel 7 to 20 m (7.5 to 22 yards) wide cuts deeply into the crater's wall; it is unclear if this channel was carved by a fluid or by landslides.
The channel is cut by a younger scarp (shown with yellow arrows pointing downhill) which approximately separates the crater's wall from its floor. This cliff can be followed for more than 3 km (2 miles) along the southern part of the crater's floor. Elsewhere in this image channels similar to the one shown here cut through (and, therefore, are younger than) the scarp, extending inside the crater's floor. This scarp may have been produced by settling of the crater's floor, maybe due to flow of ice, soil, and rocks towards the center of the crater, and/or to sublimation of underground ice.
Image PSP_001936_1370 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 25-Dec-2006. The complete image is centered at -42.7 degrees latitude, 158.5 degrees East longitude. The range to the target site was 251.6 km (157.3 miles). At this distance the image scale ranges from 25.2 cm/pixel (with 1 x 1 binning) to 50.3 cm/pixel (with 2 x 2 binning). 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 03:47 PM and the scene is illuminated from the west with a solar incidence angle of 74 degrees, thus the sun was about 16 degrees above the horizon. At a solar longitude of 155.9 degrees, the season on Mars is Northern Summer.