Status Report

Mars Odyssey THEMIS Image: Acidalia Planitia

By SpaceRef Editor

July 25, 2002

Filed under Daily Themis Pictures, Mars Odyssey THEMIS, US

Image Context:

Context image credit: NASA/Mars Orbiter Laser Altimeter (MOLA) Team

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The lineations seen in this THEMIS visible image occur in Acidalia Planitia,
and create what is referred to as “patterned ground” or “polygonal
terrain.” The lineations are fissures, or cracks in the ground and are
possibly evidence that there was once subsurface ice or water in the
region. On Earth, similar features occur when ice or water is removed from
the subsurface. The removal of material causes the ground to slump, and the
surface expression of this slumping is the presence of these fissures, which
tend to align themselves along common orientations, and in some cases, into
polygonal shapes. There are other hypotheses, not all of which involve liquid
or frozen water, regarding the formation of patterned ground. Desiccation of
wet soils on Earth forms mud cracks, which are similar in appearance to the
martian features, but occur on a much smaller scale. Alternatively, oriented
cracks form when lava flows cool. The cracks formed by this process would be
on about the same scale as those seen in this image.

The best example of polygonal terrain occurs about halfway down the
image. The largest fractures, as in other places in the image, run from the
lower left to the upper right of the image. In some cases, though, smaller
fractures occur in other orientations, creating the polygonal
terrain. Scientists have been aware of these features on the surface of Mars
since the Viking era, but the THEMIS visible camera will allow scientists to
map these features at higher resolution with more coverage over the high
latitude regions where they are most common, perhaps giving further insight
into the mechanism(s) of their formation.

[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