NASA Spacecraft Penetrates Mysteries Of Martian Ice Cap

PASADENA, Calif. -- Data from NASA's Mars Reconnaissance Orbiter (MRO) 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 MRO 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, MRO 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, SHARAD 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. SHARAD was provided by the Italian
Space Agency, and its operations are led by the InfoCom Department,
University of Rome.

To view images and learn more about MRO, visit:

http://www.nasa.gov/mro

Source: NASA