Two-Color Dunes in Meridiani Terra
NASA/JPL/University of Arizona
Two-Color Dunes in Meridiani Terra
ESP_033483_1805  Science Theme: 
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Why are these dunes different colors? Sand on Mars is typically dark in tone, as it commonly derived from volcanic rocks like lava flows. In HiRISE enhanced color, which operates in long infrared wavelengths (beyond what the human eye can detect), surfaces like these dune crests are dark blue to purple. Sand comes in sizes that are ideal for surface transport by the wind, where sand “hops” along forming bedforms, like these dunes after large amounts of time.

The lighter toned “tan” or “reddish” surfaces are indeed composed of a different material, but not as sand sized particle that makes up the bulk of these dunes. Rather, the light-toned smooth surfaces that dominate the lower, flatter areas of the dunes are a thin coating of global dust. Dust on Mars is composed of a variety of materials, including oxidized iron, like rust.

For a given wind gust, speeds are not constant at different heights. Rather, wind speeds are greater with height above the ground and wind energy drops to nearly zero at the surface. Dust persists on flatter dune areas, because wind energy there has not been sufficient to remove it, whereas “dust free” higher-lying dune crests are subject to more intense winds, which ultimately conspire to make the appearance of two-color dunes.

Written by: Matthew Chojnacki (audio: Melissa Dykhuis)   (9 April 2014)

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Acquisition date
17 September 2013

Local Mars time:
14:36

Latitude (centered)
0.493°

Longitude (East)
348.773°

Range to target site
272.4 km (170.3 miles)

Original image scale range
27.3 cm/pixel (with 1 x 1 binning) so objects ~82 cm across are resolved

Map projected scale
25 cm/pixel and North is up

Map projection
Equirectangular

Emission angle:
1.9°

Phase angle:
38.2°

Solar incidence angle
40°, with the Sun about 50° above the horizon

Solar longitude
23.1°, Northern Spring

North azimuth:
97°

Sub-solar azimuth:
20.3°
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non-map           (274MB)

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non-map           (248MB)

Merged IRB
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B&W label
Color label
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EDR products
HiView

NB
IRB: infrared-red-blue
RGB: red-green-blue
About color products (PDF)

Black & white is 5 km across; enhanced color about 1 km
For scale, use JPEG/JP2 black & white map-projected images



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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



Postscript
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.