Circular Feature in South Polar Residual Cap
NASA/JPL/University of Arizona
Circular Feature in South Polar Residual Cap
PSP_005349_0930  Science Theme: Polar Geology
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This 4 kilometer diameter feature near the edge of the South polar residual cap was recognized in Mariner 9 and Viking Orbiter images taken in the 1970s, but its origin could not be inferred. It was therefore targeted for HiRISE stereo imaging.

The bright areas in this image are covered by carbon dioxide frost, and the "swiss cheese" terrain typical of the south polar residual cap covers much of the imaged area. The dark walls of the circular depression do not have as much frost on them, and are fractured in a polygonal pattern. Apparently the surface of the walls has been extensively modified by thermal expansion and contraction of water ice.

It also appears that the "swiss cheese" terrain of the residual cap has buried the floor of the circular depression, as well as the terrain surrounding the feature, making it difficult to infer the origin of this depression. Its circular symmetry is consistent with an impact origin, but there is no evidence of a crater rim or ejecta (perhaps because they have been buried). The depression may have formed by collapse, but there is little evidence of extensional fractures that would be expected around a collapse pit. Analysis of HiRISE stereo data may help the interpretation of this feature.

Written by: Ken Herkenhoff   (15 December 2010)

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Acquisition date
17 September 2007

Local Mars time:

Latitude (centered)

Longitude (East)

Range to target site
258.5 km (161.6 miles)

Original image scale range
25.9 cm/pixel (with 1 x 1 binning) so objects ~78 cm across are resolved

Map projected scale
25 cm/pixel

Map projection

Emission angle:

Phase angle:

Solar incidence angle
71°, with the Sun about 19° above the horizon

Solar longitude
315.3°, Northern Winter

North azimuth:

Sub-solar azimuth:
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Black & white is 5 km across; enhanced color about 1 km
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NASA/JPL/University of Arizona

For information about NASA and agency programs on the Web, visit: NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, Calif., manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems is the prime contractor for the project and built the spacecraft. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona. The image data were processed using the U.S. Geological Survey’s ISIS3 software.