One of the earliest observations made by the Mars Global Surveyor
(MGS) Mars Orbiter Camera (MOC) was that the upper crust of the planet
appears to be layered to considerable depth. This was especially
apparent, early in the mission, in the walls of the the Valles Marineris
chasms. However, layered mesas and mounds within the Valles Marineris
troughs were recognized all the way back in 1972 with Mariner 9 images.
The MOC image presented here shows many tens of layers of several
meters (yards) thickness in the walls of a mesa in southern Melas
Chasma in Valles Marineris. Erosion by mass wasting--landslides--has
exposed these layers and created the dark fan-shaped deposits seen
near the middle of the image. The floor of Melas Chasma is dark and
covered with many parallel ridges and grooves (lower 1/3 of image).
In the lower left corner of the picture, a bright, circular dust devil can be
seen casting a columnar shadow toward the left. This image, illuminated
by sunlight from the right/lower right, covers an area 3 kilometers (1.9
miles) wide and 8.2 kilometers (5.1 miles) long. The scene is located
near 10.1°S, 74.4°W and was acquired on July 11, 1999. North
is toward the lower left.
Photo Credit: NASA/JPL/Malin Space Science Systems
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