NASA Spacecraft Penetrates Mysteries of Martian Ice Cap

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Jia-Rui Cook/D.C. Agle
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J.D. Harrington 202-358-5241
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Marc Airhart 512-471-2241
University of Texas, Austin
mairhart@jsg.utexas.edu

NEWS RELEASE: 2010-180 May 26, 2010

NASA SPACECRAFT PENETRATES MYSTERIES OF MARTIAN ICE CAP

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-180&cid=release_2010-180

PASADENA, Calif. -- Data from NASA's Mars Reconnaissance Orbiter have helped scientists solve
a pair of mysteries dating back four decades and provided new information about climate change on
the Red Planet.

The Shallow Radar, or SHARAD, instrument aboard the Mars Reconnaissance Orbiter revealed
subsurface geology allowing scientists to reconstruct the formation of a large chasm and a series of
spiral troughs on the northern ice cap of Mars. The findings appear in two papers in the May 27 issue
of the journal Nature.

"SHARAD is giving us a beautifully detailed view of ice deposits, whether at the poles or buried in
mid-latitudes, as they changed on Mars over the last few million years," said Rich Zurek, Mars
Reconnaissance Orbiter project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

On Earth, large ice sheets are shaped mainly by ice flow. According to this latest research, other
forces have shaped, and continue to shape, polar ice caps on Mars. The northern ice cap is a stack of
ice and dust layers up to two miles deep, covering an area slightly larger than Texas. Analyzing radar
data on a computer, scientists can peel back the layers like an onion to reveal how the ice cap evolved
over time.

One of the most distinctive features of the northern ice cap is Chasma Boreale, a canyon about as
long as Earth's Grand Canyon but deeper and wider. Some scientists believe Chasma Boreale was
created when volcanic heat melted the bottom of the ice sheet and triggered a catastrophic flood.
Others suggest strong polar winds carved the canyon out of a dome of ice.

Other enigmatic features of the ice cap are troughs that spiral outward from the center like a gigantic
pinwheel. Since the troughs were discovered in 1972, scientists have proposed several hypotheses
about how they formed. Perhaps as Mars spins, ice closer to the poles moves slower than ice farther
away, causing the semi-fluid ice to crack. Perhaps, as one mathematical model suggests, increased
solar heating in certain areas and lateral heat conduction could cause the troughs to assemble.

Data from Mars now points to both the canyon and spiral troughs being created and shaped primarily
by wind. Rather than being cut into existing ice very recently, the features formed over millions of
years as the ice sheet grew. By influencing wind patterns, the shape of underlying, older ice
controlled where and how the features grew.

"Nobody realized that there would be such complex structures in the layers," said Jack Holt, of the
University of Texas at Austin's Institute for Geophysics. Holt is the lead author of the paper focusing
on Chasma Boreale. "The layers record a history of ice accumulation, erosion and wind transport.
From that, we can recover a history of climate that's much more detailed than anybody expected."

The Mars Reconnaissance Orbiter was launched on Aug. 12, 2005. SHARAD and the spacecraft's
five other instruments began science operations in November 2006.

"These anomalous features have gone unexplained for 40 years because we have not been able to see
what lies beneath the surface," said Roberto Seu, Shallow Radar team leader at the University of
Rome. "It is gratifying to me that with this new instrument we can finally explain them."

The MRO mission is managed by JPL for the Mars Exploration Program at NASA's Headquarters in
Washington. The Shallow Radar instrument was provided by the Italian Space Agency, and its
operations are led by the InfoCom Department, University of Rome. JPL is managed for NASA by
the California Institute of Technology in Pasadena, Calif.

To view images and learn more about MRO, visit: http://www.nasa.gov/mro .

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