[meteorite-list] Mars Rovers Begin New Observations on Changing Martian Atmosphere

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 29 Aug 2007 13:18:16 -0700 (PDT)
Message-ID: <200708292018.NAA07870_at_zagami.jpl.nasa.gov>

http://newswire.ascribe.org/cgi-bin/behold.pl?ascribeid=20070829.065953&time=07%2014%20PDT&year=2007&public=0

Rovers Begin New Observations on Changing Martian Atmosphere

CHICAGO, Aug. 29 (AScribe Newswire) -- Mars rover scientists have
launched a new long-term study on the Martian atmosphere with the Alpha
Particle X-ray Spectrometer, an instrument that was originally developed
at the University of Chicago.

Thanasis Economou, Senior Scientist at Chicago's Enrico Fermi
Institute, suggested the new study after observing that the APXS
instruments aboard NASA's twin Mars rovers, Spirit and Opportunity, had
recorded fluctuations in the argon composition of the Martian
atmosphere. "The amount of argon in the atmosphere is changing
constantly," Economou said.

During warmer seasons, approximately 95 percent of the Martian
atmosphere consists of carbon dioxide. Nitrogen accounts for almost 3
percent and argon for less than 2 percent. But when winter sets in at
one of the poles, carbon dioxide freezes out of the atmosphere to form a
polar cap, causing a low-pressure system that moves air toward the pole.

Argon stays in the atmosphere and becomes enhanced because it
freezes at a much lower temperature, Economou said. An instrument on
NASA's Odyssey orbiter around Mars found that on the Mars south pole
during the winter, the argon concentration is six times higher than
during the warmer seasons.

"The amount of argon that comes with the air mass stays in the
atmosphere," he explained. "Carbon dioxide drops, so the ratio of argon
to carbon dioxide is increasing constantly until the next season."

With the onset of warmer spring and summer temperatures, the
frozen carbon dioxide evaporates back into the atmosphere, causing a
high-pressure system that pushes the air mass back toward the equator.

"The fact that we see a signal at all means there's a lot of
mixing between the polar air and the air at the tropics," said Ray
Pierrehumbert, the Louis Block Professor in Geophysical Sciences at the
University of Chicago, who specializes in the evolution of climate on
Earth and Mars. "It gives you a way of inferring aspects of the Martian
circulation that you can't observe at all with any other instrument
that's out there," he said.

Scientists are coupling the APXS measurements with additional
data collected by the orbiting Mars Odyssey spacecraft. The APXS
measures the number of argon atoms at the rover's location between the
instrument and the ground - a distance of a couple of centimeters (a few
inches). Odyssey's gamma-ray spectrometer, meanwhile, measures the argon
in a column of air extending from the upper atmosphere to the Martian
surface, but over an area spanning several hundred kilometers (a couple
hundred miles)

Spirit and Opportunity landed on Mars in January 2004. Until now,
their APXS instruments have focused on measuring the chemical content of
rocks and dust sitting on the ground. During the mission's first 90
days, for example, Opportunity's APXS contributed to the identification
and analysis of abundant sulfate salts and other minerals suggestive of
once-moist environments on the vast plain known as Meridiani Planum.

"It means that at some point the site was soaked with liquid
water," Economou said.

Opportunity's APXS also performed a key analysis of the first
meteorite ever discovered on Mars. When Opportunity encountered Heat
Shield rock in 2005, "it looked like a meteorite, but it was confirmed
with the APXS," Economou said. It was the first of at least four
meteorites that Opportunity has discovered.

"If you go to Antarctica you find lots of them because you can
spot them," he said. "On Mars also, when you have these large, flat
areas that have just sand and sand dunes, nothing else, and you now see
some suspicious rock, you know that it's not from there." Either it is
debris that has been ejected from an impact crater, or a meteorite.

In recent months, the APXS on the Spirit rover measured the
composition of soils consisting of 90 percent pure silica, which could
have formed in a hot-spring environment or some other process involving
water. The finding presents some of the best evidence yet that water
once existed at Gusev crater.

"This is a remarkable discovery," said Cornell University's Steve
Squyres, who heads the Mars rovers' science instruments team. "The fact
that we found something this new and different after nearly 1,200 days
on Mars makes it even more remarkable. It makes you wonder what else is
still out there."

Opportunity now has traveled more than six miles through some
difficult sandy terrain to reach Victoria Crater, which measures half a
mile in diameter. Rolling up to the edge of the crater, the rover has
taken images of the layered sediments, various rock types and
accumulations of sand visible at the base of the walls.

NASA engineers have scouted a possible route that Opportunity
could safely follow onto the crater floor. A dust storm in the region
has delayed plans to send Opportunity into the crater.

"This is a magnificent crater with a lot of exposed bedrocks and
walls showing geologic detail with extensive layering that makes the
team geologist very happy," Economou said. "What you can see is amazing."

- - - -

The Mars Exploration Rover mission is managed by NASA's Jet
Propulsion Laboratory, Pasadena, Calif., for the NASA Science Mission
Directorate, Washington. Additional information about the rovers is
available at http://www.nasa.gov/rovers .

CONTACT: Steve Koppes, University of Chicago Media Relations,
773-702-8366 skoppes at uchicago.edu
Received on Wed 29 Aug 2007 04:18:16 PM PDT