MGS MOC Release No. MOC2-265O, 4 December 2000
(1) Starting Conditions:
This sketch shows the initial conditions. In this case, the upper crust of Mars---portrayed by the brown and orange materials---is already layered. The "dimples" in these layers are cross-sections through buried impact craters formed by meteor impacts. In the diagrams that follow the craters and uplands at the top of this section---note the atmosphere is portrayed as golden-beige in color---will have new layered, massive, and thin mesa sedimentary units deposited upon them.
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(2) Thin layers form first:
The first sediments deposited in craters and perhaps upon the surrounding landscape are thin layers like those seen in southwestern Candor Chasma. In this sketch, four thin orange layers have been deposited at the top of the section.
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(3) Massive units form next:
Deposition of thin layered units was, in some cases, followed by deposition of thick, massive units that show very little layering and can be up to 2 km (1.2 mi) thick in some places. Examples of "massive" units can be seen in Gale Crater's central mound.
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(4) Layered and Massive units are eroded:
Some time after the thin layered units and thick massive units were deposited, they were eroded. In some cases, such as in Gale Crater's central mound, there were also periods of erosion that occurred between the deposition of layered and massive units. The erosion of these units is inferred to have occurred mostly at a time very early in martian history, but the fact that these materials usually have very few small meteorite impact craters on them today suggests that their erosion might be continuing today as well.
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(5) Thin mesa units form and erode:
After the thin layered units and thick massive units were deposited and eroded to about their present state of degradation, thin, usually dark-toned material was deposited on top of them. This material, which we call "thin mesa units", might have been deposited much more recently in martian history than the other materials. Subsequently, these too were eroded to leave small mesas and patches of severely ridged-and-grooved material behind. Examples of thin mesa units include the smooth dark material on the ridge in Valles Marineris in the release, "Light-toned Layered Outcrops in Valles Marineris Walls," MOC2-263, December 4, 2000; and the dark ridged material of Melas Chasma in "Ridged Terrain on the Floor of Melas Chasma," MOC2-232, May 22, 2000.
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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.