Light Material in Ganges Chasma Wall
NASA/JPL/UArizona
Light Material in Ganges Chasma Wall
PSP_004805_1710  Science Theme: Geologic Contacts/Stratigraphy
The troughs and chasms of the Valles Marineris system contain light toned deposits of enigmatic origin. The light materials, often layered, have variously been proposed to be volcanic ash or sediments laid down by rivers, lakes or sand dunes.

One aspect of the light toned material that has remained unclear is the timing of its deposition relative to canyon formation--was the material deposited in the troughs, or does it crop out in the walls, indicating that it existed before the Valles Marineris system formed?

This HiRISE image shows a part of the wall of Ganges Chasma. (This image, taken during the major dust storms which have raged through the summer of 2007, is grainy and low-contrast because of dust in the atmosphere). The plateau above the chasm is at the bottom of the image, with the wall of the trough descending to the north. A few fine layers, likely basalt flows, form the cap layers.

In the spur at the center of the image, light material appears to crop out, contrasting with the relatively dark material elsewhere in the wall of the trough. At least some of this material is inherently lighter than other wall rock; changes in tone occur at several sites where there are no breaks in slope. The light material appears be forming spurs and ridges similar to the surrounding rock, suggesting that it comprises at least some part of the walls. However, darker, bouldery material occurs at the same level just to the west (left) of the light patch, indicating that the light outcrop may not extend very far.

Images like this provide clues to help unravel the history of deposition and deformation in Valles Marineris, and may eventually tell a complex story. In order to fully understand what this image means, several questions must be addressed: is this light material the same as intensively layered deposits observed elsewhere? How extensive are light wall materials? Are these materials conformable (part of a continuous sequence) with the rest of the wall? More HiRISE imaging will help address these questions.

Written by: Colin Dundas  (15 August 2007)
 
Acquisition date
05 August 2007

Local Mars time
14:33

Latitude (centered)
-8.721°

Longitude (East)
307.657°

Spacecraft altitude
260.2 km (161.7 miles)

Original image scale range
26.3 cm/pixel (with 1 x 1 binning) so objects ~79 cm across are resolved

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25 cm/pixel and North is up

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Equirectangular

Emission angle
6.4°

Phase angle
33.6°

Solar incidence angle
40°, with the Sun about 50° above the horizon

Solar longitude
290.1°, Northern Winter

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Sub-solar azimuth:  339.5°
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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.