Colorful Gully Walls in Terra Sirenum
Colorful Gully Walls in Terra Sirenum
ESP_030667_1395  Science Theme: Fluvial Processes
Gullies are found on many slopes in the middle and near-polar latitudes of Mars. Although they contain no liquid water today, whether and how much water may have been involved in their formation, and any water's origin, is a matter of considerable debate.

The gullies appear relatively young, so a current process, perhaps involving ground ice or condensed volatiles—water or carbon dioxide—may be at work. Regardless, HiRISE images provide insight on gully origins and processes.

In this image, we see gullies within two craters in Terra Sirenum. One closeup shows gully alcoves touching a crater wall. Dark sand fills the alcoves and scattered boulders are apparent. Some bright rocks on the gully walls are visible, perhaps exposed by the processes that carved the gullies.

Another closeup shows gullies that are much larger than those to the north. Intriguing yellowish colors are visible on some of the walls. Determining whether this represents chemical alteration of the walls by water, or exposed, unaltered bright rock, will require further study.

Written by: Nathan Bridges (audio by Tre Gibbs)  (13 March 2013)
Acquisition date
10 February 2013

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
253.0 km (157.3 miles)

Original image scale range
25.4 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

Emission angle

Phase angle

Solar incidence angle
41°, with the Sun about 49° above the horizon

Solar longitude
261.6°, Northern Autumn

For non-map projected images
North azimuth:  96°
Sub-solar azimuth:  12.6°
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Black and white
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non-map           (624MB)

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

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’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.