[meteorite-list] Thawing 'Dry Ice' Drives Groovy Action on Mars

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 24 Jan 2013 15:57:06 -0800 (PST)
Message-ID: <201301242357.r0ONv60u027526_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.php?release=2013-034

Thawing 'Dry Ice' Drives Groovy Action on Mars
Jet Propulsion Laboratory
January 24, 2013

PASADENA, Calif. -- Researchers using NASA's Mars Reconnaissance Orbiter
see seasonal changes on far-northern Martian sand dunes caused by
warming of a winter blanket of frozen carbon dioxide.

Earth has no naturally frozen carbon dioxide, though pieces of
manufactured carbon-dioxide ice, called "dry ice," sublime directly from
solid to gas on Earth, just as the vast blankets of dry ice do on Mars.
A driving factor in the springtime changes where seasonal coverings of
dry ice form on Mars is that thawing occurs at the underside of the ice
sheet, where it is in contact with dark ground being warmed by
early-spring sunshine through translucent ice. The trapped gas builds up
pressure and breaks out in various ways.

Transient grooves form on dunes when gas trapped under the ice blanket
finds an escape point and whooshes out, carrying out sand with it. The
expelled sand forms dark fans or streaks on top of the ice layer at
first, but this evidence disappears with the seasonal ice, and summer
winds erase most of the grooves in the dunes before the next winter. The
grooves are smaller features than the gullies that earlier research
linked to carbon-dioxide sublimation on steeper dune slopes.

Similar activity has been documented and explained previously where
seasonal sheets of frozen carbon dioxide form and thaw near Mars' south
pole. Details of the different northern seasonal changes are newly
reported in a set of three papers for the journal Icarus. A video
showing some of the changes is online at
http://www.jpl.nasa.gov/video/index.php?id=1184 .

The findings reinforce growing appreciation that Mars today, however
different from its former self, is still a dynamic world, and however
similar to Earth in some respects, displays some quite unearthly processes.

"It's an amazingly dynamic process," said Candice Hansen of the
Planetary Science Institute, Tucson. She is lead author of the first of
the three new reports. "We had this old paradigm that all the action on
Mars was billions of years ago. Thanks to the ability to monitor changes
with the Mars Reconnaissance Orbiter, one of the new paradigms is that
Mars has many active processes today."

With three Martian years (six Earth years) of data in hand from the Mars
Reconnaissance Orbiter's High Resolution Imaging Science Experiment
(HiRISE) camera, the researchers report on the sequence and variety of
seasonal changes. The spring changes include outbursts of gas carrying
sand, polygonal cracking of the winter ice blanketing the dunes,
sandfalls down the faces of the dunes, and dark fans of sand propelled
out onto the ice.

"It is a challenge to catch when and how those changes happen, they are
so fast," said Ganna Portyankina of the University of Bern in
Switzerland, lead author of the second report. "That's why only now we
start to see the bigger picture that both hemispheres actually tell us
similar stories."

The process of outrushing gas that carves grooves into the northern
dunes resembles the process creating spider-shaped features in far
southern Mars, as seen in an image at
http://photojournal.jpl.nasa.gov/catalog/PIA12249, but the spiders have
not been seen in the north. The seasonal dry-ice sheets overlie
different types of terrain in the two hemispheres. In the south, diverse
terrains include the flat, erodible ground where the spiders form, but
in the north, a broad band of sand dunes encircles the permanent north
polar ice cap.

Another difference is in brightening on parts of the ice-covered dunes.
This brightening in the north results from the presence of water-ice
frost, while in the south, similar brightening is caused by fresh carbon
dioxide. The third paper of the Icarus set, by Antoine Pommerol of the
University of Bern and co-authors, reports distribution of the water
frost using the Compact Reconnaissance Imaging Spectrometer for Mars
(CRISM). The light water frost is blown around by spring winds.

The University of Arizona, Tucson, operates the HiRISE camera, which was
built by Ball Aerospace & Technologies Corp., Boulder, Colo. The Johns
Hopkins University Applied Physics Laboratory, Laurel, Md., provided and
operates CRISM. NASA's Jet Propulsion Laboratory, 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 mission, visit: http://www.nasa.gov/mro .

A slide show of Martian icy scenes is online at: http://1.usa.gov/ZoAO8I .

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

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

Dwayne Brown 202-358-1726
NASA Headquarters, Washington
dwayne.c.brown at nasa.gov

2013-034
Received on Thu 24 Jan 2013 06:57:06 PM PST