Evros Vallis and Nearby Craters
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Evros Vallis and Nearby Craters

May 20, 2007

This Martian image shows part of Evros Vallis, one of the Martian valley networks.

These more ancient valley networks may have been eroded by flowing water during a warmer, wetter period of Martian history. Many dunes are visibile along the valley floor, as well as throughout the scene and in a partially exhumed crater on the valley wall. There are multiple generations and orientations of dunes. Dune orientation reflects the dominant or prevailing wind direction. Multiple dune orientations indicate that this region has experienced different wind regimes.

An exhumed crater is one that likely formed a long time ago, was buried, and is now being re-exposed because the materials that originally covered it are being eroded away. The prominent crater on the valley wall as well as several other craters in this scene are thought to be partially exhumed.

Secondary craters are craters that form when ejecta from the primary crater hits the surface with enough energy to form another smaller crater. As seen in the subimage, secondary craters often form in clusters spatially, because ejecta thrown out of the primary crater impacts the surface near each other at approximately the same time.

Many potential secondary craters have have similar morphologies and have distinct, bright ejecta. This implies that these craters are relatively young and that their ejecta have yet to be covered by dust.

Observation Geometry

Image PSP_003273_1675 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 08-Apr-2007. The complete image is centered at -12.6 degrees latitude, 13.3 degrees East longitude. The range to the target site was 264.3 km (165.2 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 03:41 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 215.3 degrees, the season on Mars is Northern Autumn.

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