Northern Mars Landscape Actively Changing

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Guy Webster 818-354-6278
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Alan Fischer 520-382-0411
Planetary Science Institute
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Daniel Stolte 520-626-4402
University of Arizona, Tucson
stolte@email.arizona.edu

News release: 2011-039 Feb. 3, 2011

Northern Mars Landscape Actively Changing

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-039&cid=release_2011-039

Sand dunes in a vast area of northern Mars long thought to be frozen in time are changing with
both sudden and gradual motions, according to research using images from a NASA orbiter.

These dune fields cover an area the size of Texas in a band around the planet at the edge of Mars'
north polar cap. The new findings suggest they are among the most active landscapes on Mars.
However, few changes in these dark-toned dunes had been detected before a campaign of
repeated imaging by the High Resolution Imaging Science Experiment (HiRISE) camera on
NASA's Mars Reconnaissance Orbiter, which reached Mars five years ago next month.

Scientists had considered the dunes to be fairly static, shaped long ago when winds on the
planet's surface were much stronger than those seen today, said HiRISE Deputy Principal
Investigator Candice Hansen of the Planetary Science Institute, Tucson, Ariz. Several sets of
before-and-after images from HiRISE over a period covering two Martian years -- four Earth
years -- tell a different story.

"The numbers and scale of the changes have been really surprising," said Hansen.

A report by Hansen and co-authors in this week's edition of the journal Science identifies the
seasonal coming and going of carbon-dioxide ice as one agent of change, and stronger-than-
expected wind gusts as another.

A seasonal layer of frozen carbon dioxide, or dry ice, blankets the region in winter and changes
directly back to gaseous form in the spring.

"This gas flow destabilizes the sand on Mars' sand dunes, causing sand avalanches and creating
new alcoves, gullies and sand aprons on Martian dunes," she said. "The level of erosion in just
one Mars year was really astonishing. In some places, hundreds of cubic yards of sand have
avalanched down the face of the dunes."

Wind drives other changes. Especially surprising was the discovery that scars of past sand
avalanches could be partially erased by wind in just one Mars year. Models of Mars' atmosphere
do not predict wind speeds adequate to lift sand grains, and data from Mars landers show high
winds are rare.

"Perhaps polar weather is more conducive to high wind speeds," Hansen said.

In all, modifications were seen in about 40 percent of these far-northern monitoring sites over the
two-Mars-year period of the study.

Related HiRISE research previously identified gully-cutting activity in smaller fields of sand
dunes covered by seasonal carbon-dioxide ice in Mars' southern hemisphere. A report four
months ago showed that those changes coincided with the time of year when ice builds up.

"The role of the carbon-dioxide ice is getting clearer," said Serina Diniega of NASA's Jet
Propulsion Laboratory, Pasadena, Calif., lead author of the earlier report and a co-author of the
new report. "In the south, we saw before-and-after changes and connected the timing with the
carbon-dioxide ice. In the north, we're seeing more of the process of the seasonal changes and
adding more evidence linking the changes with the carbon dioxide."

Researchers are using HiRISE to repeatedly photograph dunes at all latitudes, to understand
winds in the current climate on Mars. Dunes at latitudes lower than the reach of the seasonal
carbon-dioxide ice do not show new gullies. Hansen said, "It's becoming clear that there are very
active processes on Mars associated with the seasonal polar caps."

The new findings contribute to efforts to understand what features and landscapes on Mars can
be explained by current processes, and which require different environmental conditions.

"Understanding how Mars is changing today is a key first step to understanding basic planetary
processes and how Mars changed over time," said HiRISE Principal Investigator Alfred McEwen
of the University of Arizona, Tucson, a co-author of both reports. "There's lots of current activity
in areas covered by seasonal carbon-dioxide frost, a process we don't see on Earth. It's important
to understand the current effects of this unfamiliar process so we don't falsely associate them
with different conditions in the past."

The University of Arizona Lunar and Planetary Laboratory operates the HiRISE camera, which
was built by Ball Aerospace & Technologies Corp., Boulder, Colo. JPL, a division of the
California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for
NASA's Science Mission Directorate in Washington. Lockheed Martin Space Systems, Denver,
built the orbiter. For more about the Mars Reconnaissance Orbiter, visit http://www.nasa.gov/mro
. For more about HiRISE, visit http://hirise.lpl.arizona.edu .

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