Concentric Crater Fill
This Martian image shows part of an unnamed crater located in the Northern Plains.
The intriguing landforms in the floor of this crater are known as "concentric crater fill." Such landforms are found at high latitudes (approximately above 30o from the equator), where theoretical calculations indicate that ice may exist under the surface, mixed with rocks and soil. Examples of concentric crater fill were first observed in the 1970s, in images acquired by cameras on board the Viking orbiters.
The roughly concentric ridges and throughs in the crater's floor are believed to result from compression caused by viscous flow of a thick mixture of rocks, soils, and ice inward from the crater's walls.
Impact craters with concentric fill are usually shallower than other craters. The crater shown here is approximately 12 km (7.5 miles) in diameter, and 200-400 m (220-440 yards) deep; other Martian craters of similar diameter but without concentric fill may be as deep as 700 m (765 yards). Unlike in "regular" craters, the slopes of the walls of craters with concentric fill tend to be convex, and the crater's rim is more rounded.
All these characteristics are consistent with deformation of an ice-rock mixture similar to what's observed in rock glaciers on Earth.
Image PSP_001926_2185 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 24-Dec-2006. The complete image is centered at 38.3 degrees latitude, 60.5 degrees East longitude. The range to the target site was 295.0 km (184.4 miles). At this distance the image scale is 29.5 cm/pixel (with 1 x 1 binning) so objects ~89 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 03:28 PM and the scene is illuminated from the west with a solar incidence angle of 54 degrees, thus the sun was about 36 degrees above the horizon. At a solar longitude of 155.5 degrees, the season on Mars is Northern Summer.