Gullies South of Terra Sirenum
Gullies South of Terra Sirenum
PSP_004044_1165  Science Theme: Glacial/Periglacial Processes
This image shows gullies in an unnamed crater approximately 25 kilometers (16 miles) in diameter and 1.2 kilometers (0.75 miles) deep, located south of Terra Sirenum. Several features associated with this crater suggest that, at some point in time, liquid and ice may have been present at and near the surface.

A MOC context image of this crater shows the typical lobate ejecta pattern characteristic of rampart craters, interpreted by some as indicating ice-rich or water-rich materials was excavated at the time of impact. According to this theory, the rock debris ejected from the crater and mixed with the water flowed more easily along the surface. Other possible interpretation is that fine-grained rocky material mixed with air and formed the rampart pattern in the absence of water.

The HiRISE image shows gullies not only in the inside of the crater, but also in the outside, emerging from the elevated rim of the crater (NW corner of the image). The subimage shows one of the outside gullies; illumination is from the left, downhill is up. The box-like shape of its alcove suggest this gully may have been produced by groundwater sapping, as opposed to surface runoff.

Polygon patterns are ubiquitous in this image: on the walls of the crater, on its floor, and on the walls of some of the gullies. These polygons are similar to features observed in terrestrial permafrost such as in the Arctic and Antarctic. Polygonal patterns are produced by repeated expansion and contraction of frozen soil, due to seasonal temperature cycles.

Written by: Sara Martinez-Alonso  (27 June 2007)
Acquisition date
07 June 2007

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
251.0 km (156.0 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 and North is up

Map projection

Emission angle

Phase angle

Solar incidence angle
52°, with the Sun about 38° above the horizon

Solar longitude
253.0°, Northern Autumn

For non-map projected images
North azimuth:  98°
Sub-solar azimuth:  30.2°
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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.