Defrosting Barchan Dunes
Defrosting Barchan Dunes
ESP_025118_2570  Science Theme: Seasonal Processes
This HiRISE image shows sand dunes near the eastern part of the north polar erg (sand sheet).

The dunes imaged here are similar to barchan dunes, 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.

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  (13 December 2011)
Acquisition date
05 December 2011

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
317.7 km (197.4 miles)

Original image scale range
31.8 cm/pixel (with 1 x 1 binning) so objects ~95 cm across are resolved

Map projected scale
25 cm/pixel

Map projection

Emission angle

Phase angle

Solar incidence angle
63°, with the Sun about 27° above the horizon

Solar longitude
39.2°, Northern Spring

For non-map projected images
North azimuth:  103°
Sub-solar azimuth:  314.0°
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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.