Boulders in Gully Alcoves
Boulders in Gully Alcoves
ESP_039747_1090  Science Theme: Mass Wasting Processes
Gullies are often found on steep slopes. In the winter, this area is covered with a layer of carbon dioxide ice (dry ice). In the spring, when the ice warms up and transitions to gas, it dislodges material on the slope, forming a gully.

In general, this process works best on fine material, leaving behind large boulders. These boulders can be seen collected in the gully alcoves. Occasionally, boulders slide or roll downhill, like those sprinkled downslope in this image.

This set of gullies is found at -71 degrees latitude in the Southern Hemisphere.

Written by: Candy Hansen (audio: Tre Gibbs)  (11 February 2015)
Acquisition date
18 January 2015

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
250.8 km (155.9 miles)

Original image scale range
25.1 cm/pixel (with 1 x 1 binning) so objects ~75 cm across are resolved

Map projected scale
25 cm/pixel

Map projection

Emission angle

Phase angle

Solar incidence angle
54°, with the Sun about 36° above the horizon

Solar longitude
274.6°, Northern Winter

For non-map projected images
North azimuth:  100°
Sub-solar azimuth:  38.8°
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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.