MGS MOC Release No. MOC2-263, 4 December 2000
From mosaic of Viking images 066A23, 066A25, 066A26, 066A28, 066A30
Subframe MOC M17-00467
Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images have confirmed the presence of light- and dark-toned layered sedimentary rock outcrops in the Valles Marineris, but they have also revealed many more than were previously known and they have shown several good examples that these materials are coming out of the walls of the Valles Marineris chasms. The fact that these materials come out of the chasm walls means that the layers do not represent lakes (or volcanic debris) that formed in the Valles Marineris. Instead, they represent materials deposited and buried long before there ever was a Valles Marineris. They are seen now because of the faulting and erosion that opened up and widened the Valles Marineris troughs.
Picture A is a mosaic of Viking 1 orbiter images taken in 1976 showing a portion of the wall that separates western Ophir Chasma from western Candor Chasma in the Valles Marineris. This area is located around 5°S, 74°W. The white box labeled "M17-00467" shows the location of a subframe of MOC image M17-00467 that was acquired in July 2000 to allow scientists to examine one of the many bright patches (indicated by small arrows) seen on the walls of Valles Marineris.
Picture B is a subframe of MOC image M17-00467, showing a high-resolution view of one of the bright patches on the walls of Candor Chasma. The MOC image reveals that the bright material indeed consists of light-toned layered rock similar to other outcrops thought to be sedimentary in origin found throughout the Valles Marineris. The dark ridge running from top center to center-left in this view is mantled by a smooth, dark material that covers additional light-toned layered rock. The observation that these kinds of bright layered rock occur within the walls of the Valles Marineris indicate that the materials are very, very old. They have been buried under several kilometers (i.e., more than a mile) of additional layered rock, all of which is beneath plains thought to be more than 2.5 to 3.5 billion years old. These relationships suggest that all of the layered sedimentary rocks observed on Mars by MGS MOC may date back to the earliest parts of martian history, between 3.5 and 4.5 billion years ago.
In both pictures, north is toward the top. Sunlight illuminates the Viking image context (Picture A) from the top/right; the MOC image (Picture B) is illuminated from the upper left.
(A) NE West Candor Chasma Walls/Context:
Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.
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