NASA Orbiter Catches Mars Sand Dunes In Motion

WASHINGTON -- Images from NASA's Mars Reconnaissance Orbiter (MRO)
show sand dunes and ripples moving across the surface of Mars at
dozens of locations and shifting up to several yards. These
observations reveal the planet's sandy surface is more dynamic than
previously thought.

"Mars either has more gusts of wind than we knew about before, or the
winds are capable of transporting more sand," said Nathan Bridges,
planetary scientist at the Johns Hopkins University's Applied Physics
Laboratory in Laurel, Md., and lead author of a paper on the finding
published online in the journal Geology. "We used to think of the
sand on Mars as relatively immobile, so these new observations are
changing our whole perspective."

While red dust is known to swirl all around Mars in storms and dust
devils, the planet's dark sand grains are larger and harder to move.
Less than a decade ago, scientists thought the dunes and ripples on
Mars either did not budge or moved too slowly for detection.

MRO was launched in 2005. Initial images from the spacecraft's High
Resolution Imaging Science Experiment (HiRISE) camera documented only
a few cases of shifting sand dunes and ripples, collectively called
bedforms. Now, after years of monitoring the martian surface, the
spacecraft has documented movements of a few yards or meters per year
in dozens of locations across the planet.

The air on Mars is thin, so stronger gusts of wind are needed to push
a grain of sand. Wind-tunnel experiments have shown that a patch of
sand would take winds of about 80 mph to move on Mars compared with
only 10 mph on Earth. Measurements from the meteorology experiments
on NASA's Viking landers in the 1970s and early 1980s, in addition to
climate models, showed such winds should be rare on Mars.

The first hints that Martian dunes move came from NASA's Mars Global
Surveyor, which operated from 1997 to 2006. But the spacecraft's
cameras lacked the resolution to definitively detect the changes.
NASA's Mars Exploration Rovers also detected hints of shifting sand
when they touched down on the red planet's surface in 2004. The
mission team was surprised to see grains of sand dotting the rovers'
solar panels. They also witnessed the rovers' track marks filling in
with sand.

"Sand moves by hopping from place to place," said Matthew Golombek, a
co-author of the new paper and a member of the Mars Exploration Rover
and MRO teams at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
"Before the rovers landed on Mars, we had no clear evidence of sand moving."

Not all of the sand on Mars is blowing in the wind. The study also
identifies several areas where the bedforms did not move.

"The sand dunes where we didn't see movement today could have larger
grains, or perhaps their surface layers are cemented together," said
Bridges, who also is a member of the HiRISE team. "These studies show
the benefit of long-term monitoring at high resolution."

According to scientists, the seemingly stationary areas might move on
much larger time scales, triggered by climate cycles on Mars that
last tens of thousands of years. The tilt of Mars' axis relative to
its orbital plane can vary dramatically. This, combined with the oval
shape of Mars' orbit, can cause extreme changes in the Martian
climate, much greater than those experienced on Earth. Mars may once
have been warm enough that the carbon dioxide now frozen in the polar
ice caps could have been free to form a thicker atmosphere, leading
to stronger winds capable of transporting sand.

HiRISE is operated by the University of Arizona in Tucson. The
instrument was built by Ball Aerospace & Technologies Corp. of
Boulder, Colo. The Mars Exploration Rovers Opportunity and Spirit
were built by JPL. JPL also manages the MRO and Mars Exploration
Rover projects for NASA's Science Mission Directorate in Washington.
Lockheed Martin Space Systems of Denver is NASA's industry partner
for the MRO Project and built the spacecraft.

MRO images and additional information is available online at:


For more information about NASA Mars missions, visit the Web at:



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