Defrosting Polar Sand Dunes
Defrosting Polar Sand Dunes
PSP_007043_2650  Science Theme: Seasonal Processes
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)
Acquisition date
27 January 2008

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
317.4 km (197.2 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/pixel

Map projection

Emission angle

Phase angle

Solar incidence angle
75°, with the Sun about 15° above the horizon

Solar longitude
23.4°, Northern Spring

For non-map projected images
North azimuth:  127°
Sub-solar azimuth:  309.3°
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Black & white is 5 km across; enhanced color about 1 km
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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. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona.