Well-Speckled Polar Dunes
NASA/JPL/University of Arizona
Well-Speckled Polar Dunes
ESP_025579_2580  Science Theme: Other
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These barchan (crescent-shaped) sand dunes are found within the North Polar erg of Mars. This type of dune provides a great record of the wind environment when they formed and moved: barchan dunes' horns point downwind. Although the question of present-day sand motion is still open, it appears possible that these dunes are active (when not covered in frost) as their crestlines are very sharp and their slipfaces (the inner curved region between the horns/downwind surface) appears very smooth and steep.

In this image, taken during the northern spring season, the dunes and ground are still covered in seasonal frost. The speckled appearance is due to the warming of the area -- as the carbon dioxide frost and ice on the dunes warms, small areas warm and sublimate (turn from solid to gas) faster, creating small jets that expose/deposit dark sand and dust onto the surface. Notice that there are no spots on the ground between the dunes -- that is because the ground stays more uniformly cold, unlike the darker dune sand.

As spring continues, more spots will appear on the dunes until, suddenly, all of the frost on the dunes and ground will be gone and the dark dune sand will be exposed until next winter.
Written by: Serina Diniega   (22 February 2012)

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Acquisition date
10 January 2012

Local Mars time:

Latitude (centered)

Longitude (East)

Range to target site
318.6 km (199.1 miles)

Original image scale range
63.7 cm/pixel (with 2 x 2 binning) so objects ~191 cm across are resolved

Map projected scale
50 cm/pixel

Map projection

Emission angle:

Phase angle:

Solar incidence angle
59°, with the Sun about 31° above the horizon

Solar longitude
55.2°, Northern Spring

North azimuth:

Sub-solar azimuth:
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Black & white is 5 km across; enhanced color about 1 km
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All of the images produced by HiRISE and accessible on this site are within the public domain: there are no restrictions on their usage by anyone in the public, including news or science organizations. We do ask for a credit line where possible:
NASA/JPL/University of Arizona

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.