[meteorite-list] Mars Reconnaissance Orbiter Observations Point to 'Dry Ice' Snowfall on Mars

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 11 Sep 2012 12:04:35 -0700 (PDT)
Message-ID: <201209111904.q8BJ4aQ4013455_at_zagami.jpl.nasa.gov>

Sept. 11, 2012

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

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

RELEASE: 12-315

NASA ORBITER OBSERVATIONS POINT TO 'DRY ICE' SNOWFALL ON MARS

PASADENA, Calif. -- NASA's Mars Reconnaissance Orbiter (MRO) data have
given scientists the clearest evidence yet of carbon dioxide
snowfalls on Mars. This reveals the only known example of carbon
dioxide snow falling anywhere in our solar system.

Frozen carbon dioxide, better known as "dry ice," requires
temperatures of about minus 193 degrees Fahrenheit (minus 125
Celsius), which is much colder than needed for freezing water. Carbon
dioxide snow reminds scientists that although some parts of Mars may
look quite Earth-like, the Red Planet is very different. The report
is being published in the Journal of Geophysical Research.

"These are the first definitive detections of carbon dioxide snow
clouds," said the report's lead author Paul Hayne of NASA's Jet
Propulsion Laboratory (JPL) in Pasadena, Calif. "We firmly establish
the clouds are composed of carbon dioxide -- flakes of Martian air --
and they are thick enough to result in snowfall accumulation at the
surface."

The snow falls occurred from clouds around the Red Planet's south pole
in winter. The presence of carbon dioxide ice in Mars' seasonal and
residual southern polar caps has been known for decades. Also, NASA's
Phoenix Lander mission in 2008 observed falling water-ice snow on
northern Mars.

Hayne and six co-authors analyzed data gained by looking at clouds
straight overhead and sideways with the Mars Climate Sounder, one of
six instruments on MRO. This instrument records brightness in nine
wavebands of visible and infrared light as a way to examine particles
and gases in the Martian atmosphere.

The data provide information about temperatures, particle sizes and
their concentrations. The new analysis is based on data from
observations in the south polar region during southern Mars winter in
2006-2007, identifying a tall carbon dioxide cloud about 300 miles
(500 kilometers) in diameter persisting over the pole and smaller,
shorter-lived, lower-altitude carbon dioxide ice clouds at latitudes
from 70 to 80 degrees south.

"One line of evidence for snow is that the carbon dioxide ice
particles in the clouds are large enough to fall to the ground during
the lifespan of the clouds," co-author David Kass of JPL said.
"Another comes from observations when the instrument is pointed
toward the horizon, instead of down at the surface. The infrared
spectra signature of the clouds viewed from this angle is clearly
carbon dioxide ice particles and they extend to the surface. By
observing this way, the Mars Climate Sounder is able to distinguish
the particles in the atmosphere from the dry ice on the surface."

Mars' south polar residual ice cap is the only place on Mars where
frozen carbon dioxide persists on the surface year-round. Just how
the carbon dioxide from Mars' atmosphere gets deposited has been in
question. It is unclear whether it occurs as snow or by freezing out
at ground level as frost. These results show snowfall is especially
vigorous on top of the residual cap.

"The finding of snowfall could mean that the type of deposition --
snow or frost -- is somehow linked to the year-to-year preservation
of the residual cap," Hayne said.

JPL provided the Mars Climate Sounder instrument and manages the MRO
Project for NASA's Science Mission Directorate in Washington.

For more information about MRO, visit:

http://www.nasa.gov/mro
        
-end-
Received on Tue 11 Sep 2012 03:04:35 PM PDT