[meteorite-list] MRO Spacecraft Observes Further Evidence of Dry Ice Gullies on Mars

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 10 Jul 2014 16:08:48 -0700 (PDT)
Message-ID: <201407102308.s6AN8nfO003972_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.php?release=2014-226

NASA Spacecraft Observes Further Evidence of Dry Ice Gullies on Mars
Jet Propulsion Laboratory
July 10, 2014

Repeated high-resolution observations made by NASA's Mars Reconnaissance
Orbiter (MRO) indicate the gullies on Mars' surface are primarily formed
by the seasonal freezing of carbon dioxide, not liquid water.

The first reports of formative gullies on Mars in 2000 generated
excitement and headlines because they suggested the presence of liquid
water on the Red Planet, the eroding action of which forms gullies here
on Earth. Mars has water vapor and plenty of frozen water, but the
presence of liquid water on the neighboring planet, a necessity for all
known life, has not been confirmed. This latest report about gullies has
been posted online by the journal Icarus.

"As recently as five years ago, I thought the gullies on Mars indicated
activity of liquid water," said lead author Colin Dundas of the U.S.
Geological Survey's Astrogeology Science Center in Flagstaff, Arizona.
"We were able to get many more observations, and as we started to see
more activity and pin down the timing of gully formation and change, we
saw that the activity occurs in winter."

Dundas and collaborators used the High Resolution Imaging Science
Experiment (HiRISE) camera on MRO to examine gullies at 356 sites on
Mars, beginning in 2006. Thirty-eight of the sites showed active gully
formation, such as new channel segments and increased deposits at the
downhill end of some gullies.

Using dated before-and-after images, researchers determined the timing
of this activity coincided with seasonal carbon-dioxide frost and
temperatures that would not have allowed for liquid water.

Frozen carbon dioxide, commonly called dry ice, does not exist naturally
on Earth, but is plentiful on Mars. It has been linked to active
processes on Mars such as carbon dioxide gas geysers and lines on sand
dunes plowed by blocks of dry ice. One mechanism by which carbon-dioxide
frost might drive gully flows is by gas that is sublimating from the
frost providing lubrication for dry material to flow. Another may be
slides due to the accumulating weight of seasonal frost buildup on steep
slopes.

The findings in this latest report suggest all of the fresh-appearing
gullies seen on Mars can be attributed to processes currently underway,
whereas earlier hypotheses suggested they formed thousands to millions
of years ago when climate conditions were possibly conducive to liquid
water on Mars.

Dundas's co-authors on the new report are Serina Diniega of NASA's Jet
Propulsion Laboratory in Pasadena, California, and Alfred McEwen of the
University of Arizona, Tucson.

"Much of the information we have about gully formation, and other active
processes, comes from the longevity of MRO and other orbiters," said
Diniega. "This allows us to make repeated observations of sites to
examine surface changes over time."

Although the findings about gullies point to processes that do not
involve liquid water, possible action by liquid water on Mars has been
reported in the past year in other findings from the HiRISE team. Those
observations were of a smaller type of surface-flow feature.

An upcoming special issue of Icarus will include multiple reports about
active processes on Mars, including smaller flows that are strong
indications of the presence of liquid water on Mars today.

"I like that Mars can still surprise us," Dundas said. "Martian gullies
are fascinating features that allow us to investigate a process we just
don't see on Earth."

HiRISE is operated by the University of Arizona, Tucson. The instrument
was built by Ball Aerospace & Technologies Corp. of Boulder, Colorado.
The Mars Reconnaissance Orbiter Project is managed for NASA's Science
Mission Directorate in Washington, by JPL, a division of the California
Institute of Technology, Pasadena.

For more information about HiRISE, visit: http://hirise.lpl.arizona.edu

Additional information about MRO is online at: http://www.nasa.gov/mro

For recent findings suggesting the presence of liquid water on Mars,
visit:

http://go.nasa.gov/1q1VRLS

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

J.D. Harrington
NASA Headquarters, Washington
202-358-5241
j.d.harrignton at nasa.gov

2014-226
Received on Thu 10 Jul 2014 07:08:48 PM PDT