Defrosting Polar Sand Dunes
NASA/JPL/University of Arizona

Defrosting Polar Sand Dunes
PSP_007043_2650  Science Theme: Seasonal Processes
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This image shows dunes near the north pole of Mars. The north pole is surrounded by a vast "sea" of basaltic sand dunes, and the dunes imaged here are similar to barchan dunes that are commonly found in desert regions on Earth.

Barchan dunes are generally crescent-shaped with a steep slip face bordered by horns oriented in the downwind direction. Barchan dunes form by winds blowing mainly in one direction and thus are good indicators of the dominant wind direction when the dunes formed. In this case, the strongest winds blew approximately south to north.

The dunes and surrounding surface appear bright because they are covered with seasonal frost left over from the northern hemisphere winter. Sunlight is now falling on the north polar region, and carbon dioxide frost that accumulated during winter is sublimating (going directly from solid to gas) and the surface beneath the frost is being revealed. Composed primarily of basaltic sand, the dunes will appear dark during the northern hemisphere summer. The dark spots are areas where some of this frost has begun to sublime away, and/or where wind has exposed the underlying dark sand.

Written by: Maria Banks   (27 February 2008)

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Acquisition date:27 January 2008 Local Mars time:12:17 PM
Latitude (centered):84.689° Longitude (East):0.774°
Range to target site:319.7 km (199.8 miles)Original image scale range:32.0 cm/pixel (with 1 x 1 binning) so objects ~96 cm across are resolved
Map projected scale:25 cm/pixelMap projection:Polarstereographic
Emission angle:4.8° Phase angle:78.1°
Solar incidence angle:75°, with the Sun about 15° above the horizon Solar longitude:23.4°, Northern Spring
For non-map projected products:
North azimuth:127° Sub-solar azimuth:309.3°
For map-projected products
North azimuth:269.2°Sub solar azimuth:93.57°

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For information about NASA and agency programs on the Web, visit: http://www.nasa.gov. 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.