Gullies and… Gullies? in Terra Sirenum

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Caption:

Figure 1
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This HiRISE image ( PSP_001697_1390 ) shows part of an unnamed crater, itself located inside the much larger Newton Crater, in Terra Sirenum. This unnamed crater is approximately 7 km in diameter (over 4 miles) and some 700 m (760 yards) deep. Numerous gully systems are visible on the east- and south-facing walls of the crater; their characteristics are astonishingly diverse, though.

The image's subset (figure 1) covers an area of nearly 610 x 740 m (670 x 800 yards). Downhill is toward the bottom of the image, north is up; illumination is from the northwest. This subset depicts several gullies or troughs carved in the southwest-facing wall of the crater.

These troughs are extremely rectilinear, lack tributaries, and do not seem to have terminal fan deposits: they terminate rather abruptly, some of them in a spatula-like shape. Their characteristics contrast sharply with those of gully systems elsewhere in this same crater, which are sinuous, have numerous tributaries, and show distinct fan deposits.

HiRISE is unveiling the large diversity exhibited by Martian gully systems, thanks to its high-resolution, stereo, and color capabilities. The diverse types of gullies observed may have been produced by different mechanisms. Current leading hypotheses explaining the origin of gullies include erosion from seepage or eruption of water from a subsurface aquifer, melting of ground ice, or surface snow; and dry landslides.

Observation Geometry
Acquisition date: 12 December 2006
Local Mars time: 3:40 PM
Degrees latitude (centered): -40.8 °
Degrees longitude (East): 200.2 °
Range to target site: 256.4 km (160.3 miles)
Original image scale range: 51.3 cm/pixel(with 2 x 2 binning) so objects ~154 cm across are resolved
Map-projected scale: 50 cm/pixel and north is up
Map-projection: EQUIRECTANGULAR
Emission angle: 9.0 °
Phase angle: 81.6 °
Solar incidence angle: 74 °, with the Sun about 16 ° above the horizon
Solar longitude: 146.3 °, Northern Summer

Background Info:

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, is the prime contractor for the project and built the spacecraft. The High Resolution Imaging Science Experiment is operated by the University of Arizona, Tucson, and the instrument was built by Ball Aerospace and Technology Corp., Boulder, Colo.

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