[meteorite-list] Northern Mars Landscape Actively Changing

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 3 Feb 2011 18:11:26 -0800 (PST)
Message-ID: <201102040211.p142BQIa024301_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2011-039

Northern Mars Landscape Actively Changing
Jet Propuslion Laboratory
February 03, 2011

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 <http://hirise.lpl.arizona.edu> .

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

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

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

2011-039
Received on Thu 03 Feb 2011 09:11:26 PM PST