Mars Global Surveyor
Mars Orbiter Camera
Sketches Illustrating Processes that Might have Formed Layered Units,
Massive Units, and Thin Mesa Units in Martian Terrain
MGS MOC Release No. MOC2-265P, 4 December 2000
(1) Formation of Layered Units:
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(2) Formation of Massive Units
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These simplified sketches portray cross-sections through the upper few
kilometers (upper few miles) of the martian crust and illustrate
the key processes that might have contributed to the formation
of layered and massive sedimentary rock units on Mars. Two basic
processes are portrayed:
- Air Fall---deposition of sediment as dust settling out of the atmosphere, and
- Water---deposition in bodies of water such as crater lakes and shallow seas.
The chief source for sediment in both cases may be a combination of
materials produced by explosive volcanism, meteorite impact, and
weathering and erosion. Thin layers of regular thickness, as seen in
western Candor Chasma, seem most likely
to have formed underwater in lakes or perhaps shallow seas, most of
them occupying craters. In the "Air Fall" case, a mechanism to create
thin layers of regular thickness and properties is needed that would
mimic the type of deposition that occurs in bodies of water. In this
scenario, the atmosphere's pressure varies on a regular basis from
something that is hundreds of times thicker than it is at present, to
something that is perhaps only tens of times (or less) thicker than it
is today. As the atmospheric pressure goes up, it could carry more
dust to be deposited, as it goes down, there would be less dust
deposited. The net result would be the creation of layers. Of course,
it is possible that both kinds of processes were at work on early
Mars, but there is no way to distinguish these by examining images and
other data from orbiting spacecraft alone.
Ultimately, geologists will have to go to Mars to investigate the
changes in ancient martian environments recorded in these rocks.
These illustrations and the processes they portray were inferred
from study of Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC)
images. The illustrations represent a synthesis of ideas described
in the December 8, 2000, paper, "Sedimentary Rocks of Early Mars,"
in Science.
Artwork by Malin Space Science Systems;
Credit: NASA/JPL/Malin Space Science Systems
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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