Elizabeth Barrette (ysabetwordsmith) wrote,
Elizabeth Barrette
ysabetwordsmith

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The Dunes of Mars

Apparently the Martian surface is more malleable than expected.


Northern Mars Landscape Actively Changing

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
hirise.lpl.arizona.edu .

Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif.
guy.webster@jpl.nasa.gov

Alan Fischer 520-382-0411
Planetary Science Institute
fischer@psi.edu

Daniel Stolte 520-626-4402
University of Arizona, Tucson
stolte@email.arizona.edu


- end -

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