Status Report

Mars Odyssey THEMIS Image: Dao Vallis

By SpaceRef Editor
August 7, 2002
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Medium image for 20020807a

Image Context:
Context image for 20020807a
Context image credit: NASA/Mars Orbiter Laser Altimeter (MOLA) Team
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This THEMIS visible image shows Dao Vallis, a large outflow channel that
starts on the southeast flank of a large volcano called Hadriaca Patera and
runs for 1000 kilometers southwest into the Hellas impact basin. The channel
is up to 20 kilometers wide near its source, but narrows downstream. As can
be seen in the context image, the part of Dao Vallis imaged by THEMIS is
actually one of the most narrow.

It is believed that Dao Vallis was carved by a combination of surface and
subsurface flow. Evidence for both of these processes can be seen in this
image. The size of the channel, its steep walls, and the lineations at the
bottom of the channel indicate that it was carved by surface flow of
water. The erosional morphology near the center of the image, on the northern
edge of the channel indicates that groundwater sapping was also a minor
process. Subsidence of the surface into the quasi-circular depressions seen
in this image is indicative of this process.

Because the source region of Dao Vallis is the flank of a volcano, it is
most likely that the water that carved the channel erupted from the subsurface
as geothermal heating by nearby magma melted large amounts of ground
ice. Some of this water made it to the surface and carved the channel, while
some water flowed below ground and caused the sapping features evident in this
THEMIS image.

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[Source: ASU THEMIS Science Team]

Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

NASA’s Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA’s Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

Image Credit: NASA/JPL/Arizona State University

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ParameterValue ParameterValue
Latitude-35.4 &nbsp InstrumentVIS
Longitude90.9E (269.1W) &nbsp Resolution (m)19
Image Size (pixels)3061×1199 &nbsp Image Size (km)58.2×22.8
Solar Longitude329.6 &nbsp Emission Angle2.9
Incidence Angle67.2 &nbsp Phase Angle69.2
North Azimuth262.9 &nbsp Slant Distance428.4 km
Local Solar Time8.8 &nbsp Sun Azimuth114.8

SpaceRef staff editor.