Mars Orbiter Examines 'Lace' and 'Lizard Skin' Terrain
SAN FRANCISCO - Scrutiny by NASA's newest Mars orbiter is helping scientists
learn the stories of some of the weirdest landscapes on Mars, as well as more
familiar-looking parts of the Red Planet.
One type of landscape near Mars' south pole is called "cryptic terrain" because
it once defied explanation, but new observations bolster and refine recent
interpretations of how springtime outbursts of carbon-dioxide gas there sculpt
intricate patterns and paint seasonal splotches.
"A lot of Mars looks like Utah, but this is an area that looks nothing like Planet
Earth," said Candice Hansen of NASA's Jet Propulsion Laboratory, Pasadena, Calif.,
deputy principal investigator for the High Resolution Imaging Science Experiment
(HiRISE) camera on NASA's Mars Reconnaissance Orbiter.
In addition to radially branching patterns called "spiders," which had been detected
by an earlier Mars orbiter, other intriguing ground textures in the area appear in the
new images. "In some places, the channels form patterns more like lace. In others, the
texture is reminiscent of lizard skin," Hansen said.
Results from all six instruments on the Mars Reconnaissance Orbiter, which reached Mars
last year, are described in dozens of presentations this week by planetary scientists in
San Francisco at the fall meeting of the American Geophysical Union.
By taking stereo pictures of a target area from slightly different angles during different
orbits, HiRISE can show the surface in three dimensions. Channels found to widen as they
run uphill in the cryptic terrain region testify that the channels are cut by a gas, not a liquid.
Earlier evidence for jets of gas active in the region came from fan-shaped blotches appearing
seasonally, which scientists interpret as material fallen to the surface downwind of vents
where the gas escapes. Some of the fans are dark, others bright. "The dark fans are probably
dust, but the exact composition of the brighter fans had remained unknown until now," said
Tim Titus of the U.S. Geological Survey's Astrogeology Team, Flagstaff, Ariz.
Observations by the new orbiter's Compact Reconnaissance Imaging Spectrometer for Mars suggest
that the bright fans are composed of carbon-dioxide frost. Here's the story researchers now
propose: Spring warms the ground under a winter-formed coating of carbon dioxide ice. Thawing
at the base of the coating generates carbon-dioxide gas, which carves channels as it pushes its
way under the ice to a weak spot where it bursts free. The jet of escaping gas carries dust aloft
and also cools so fast from expanding rapidly that a fraction of the carbon dioxide refreezes and
falls back to the surface as frost.
The processes creating the cryptic terrain are current events on Mars. Repeated HiRISE observations
of the same target area show the downwind fans can form and grow perceptibly in less than five days.
Other new findings from the Mars Reconnaissance Orbiter reveal processes of Martian environments
long ago. A team including Chris Okubo of the University of Arizona, Tucson, used stereo HiRISE
images to examine layered deposits inside Mars' Candor Chasma, part of Valles Marineris, the largest
canyon system in the solar system.
"The high-resolution structural map allowed us to interpret the geological history of the area,"
Okubo said. "The layers are tilted in a way that tells us they are younger than the canyon."
Spectrometer studies of the composition of these deposits had indicated water played a role in their
formation, but their age relative to the formation of the canyon had been uncertain. The new findings
suggest water was present after the canyon formed.
JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance
Orbiter mission for the NASA Science Mission Directorate, Washington. Lockheed Martin Space Systems,
Denver, is the prime contractor for the project and built the spacecraft. The University of Arizona
operates the HiRISE camera, which was built by Ball Aerospace and Technology Corp., Boulder, Colo.
The Compact Reconnaissance Imaging Spectrometer for Mars team, led by Johns Hopkins University's
Applied Physics Laboratory, includes expertise from universities, government agencies and small
businesses in the United States and abroad.
Media contact: Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif.