Active Gullies on Martian Sand Dunes
NASA/JPL/University of Arizona
Active Gullies on Martian Sand Dunes
ESP_020797_1280  Science Theme: Seasonal Processes
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The dark sand dunes here are eroded in many places, forming gullies. Some of these gullies were not present in prior images of this spot, or have grown in size.

Monitoring of dune gullies by HiRISE has shown us when the gullies are active: in the winter or early spring! This was a surprise, because the gullies look like ones on Earth that are formed by flowing water or wet debris.

It is far too cold for water to be liquid in the Martian winter, but there is carbon dioxide frost (dry ice) on the ground, lasting through the spring at high latitudes. This frost may serve to reduce grain-to-grain friction, allowing the sand to flow on the steep slopes.

Written by: Alfred McEwen  (12 January 2011)
 
Acquisition date
03 January 2011

Local Mars time
15:49

Latitude (centered)
-51.964°

Longitude (East)
18.200°

Spacecraft altitude
252.1 km (156.7 miles)

Original image scale range
25.2 cm/pixel (with 1 x 1 binning) so objects ~76 cm across are resolved

Map projected scale
25 cm/pixel and North is up

Map projection
Equirectangular

Emission angle
0.3°

Phase angle
60.6°

Solar incidence angle
60°, with the Sun about 30° above the horizon

Solar longitude
210.1°, Northern Autumn

For non-map projected images
North azimuth:  97°
Sub-solar azimuth:  24.1°
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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
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.