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This HiRISE image (PSP_002169_1940) captures one of the cleaner portions of the interior wall of the caldera at the top of Tharsis Tholus.

Tharsis Tholus is an intermediate sized shield volcano, much smaller than giants such as Olympus Mons, but still large by terrestrial standards. While relatively dust-free, this section of the caldera wall is still extensively covered by dust that is being sculpted into curious shapes by the wind and by gravity.

Observation Toolbox
Acquisition date: 1 January 2007
Local Mars time: 3:33 PM
Degrees latitude (centered): 13.6°
Degrees longitude (East): 268.8°
Range to target site: 274.4 km (171.5 miles)
Original image scale range: 54.9 cm/pixel (with 2 x 2 binning) so objects ~165 cm across are resolved
Map-projected scale: 50 cm/pixel and north is up
Map-projection: EQUIRECTANGULAR
Emission angle: 13.3°
Phase angle: 66.1°
Solar incidence angle: 53°, with the Sun about 37° above the horizon
Solar longitude: 165.5°, Northern Summer

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, is the prime contractor for the project and built the spacecraft. The High Resolution Imaging Science Experiment is operated by the University of Arizona, Tucson, and the instrument was built by Ball Aerospace and Technology Corp., Boulder, Colo.