Figure 1
Researchers' goal in taking this image was to look for boulders in the
large ripples formed by an ancient catastrophic flood in Mars' Athabasca
Vallis. The Mars Orbiter Camera on NASA's Mars Global Surveyor spacecraft
captured this image on Dec. 25, 2003, with use of an enhanced-resolution
technique called compensated pitch and roll targeted observation.
The flood-deposited megaripples had been seen in earlier, lower-resolution
images from the same camera. They are the only good examples known of
ripples formed in a giant catastrophic flood anywhere on Mars. Their
presence indicates that large amounts of water poured rapidly through
this area, based on resemblance to similar megaripples in catastrophic
flood sites on Earth. The ripples in Athabasca Vallis were buried for
some period and later exhumed. Strange, round features on top of some of
the ripples and the adjacent plains are products of erosion and removal
of the overlying layer. Finding boulders in the ripples would help
constrain estimates of the power of the floods. However, the image does
not show boulders in the ripples, implying either that the rocks that make
up these features are smaller than about 1 to 2 meters (3 to 7 feet) in
diameter or that the ripple sediments have not been completely exhumed.
The image covers an area 3 kilometers (2 miles) wide, near 9.5 degrees
north latitude and 203.7 degrees west longitude. Pixel size is about 1.5
meters (5 feet) by one-half meter (1.6 feet). North is up and sunlight
illuminates the scene from the lower left.
Mars Global Surveyor is managed by NASA's Jet Propulsion Laboratory, a
division of the California Institute of Technology, Pasadena, for the
NASA Science Mission Directorate, Washington.