Some of Mars' Missing Carbon Dioxide May be Buried

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

Lauren Gold 607-255-9736
Cornell University, Ithaca, N.Y.
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Geoffrey Brown 240-228-5618
Johns Hopkins University Applied Physics Laboratory, Laurel, Md.
Geoffrey.Brown@jhuapl.edu

News release: 2011-071 March 8, 2011

Some of Mars' Missing Carbon Dioxide May be Buried

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-071&cid=release_2011-071

HOUSTON -- Rocks on Mars dug from far underground by crater-blasting impacts are providing
glimpses of one possible way Mars' atmosphere has become much less dense than it used to be.

At several places where cratering has exposed material from depths of about 5 kilometers (3
miles) or more beneath the surface, observations by a mineral-mapping instrument on NASA's
Mars Reconnaissance Orbiter indicate carbonate minerals.

These are not the first detections of carbonates on Mars. However, compared to earlier findings,
they bear closer resemblance to what some scientists have theorized for decades about the
whereabouts of Mars' "missing" carbon. If deeply buried carbonate layers are found to be
widespread, they would help answer questions about the disappearance of most of ancient Mars'
atmosphere, which is deduced to have been thick and mostly carbon dioxide. The carbon that
goes into formation of carbonate minerals can come from atmospheric carbon dioxide.

"We're looking at a pretty lucky location in terms of exposing something that was deep beneath
the surface," said planetary scientist James Wray of Cornell University, Ithaca, N.Y., who
reported the latest carbonate findings today at the Lunar and Planetary Science Conference near
Houston. Huygens crater, a basin 467 kilometers (290 miles) in diameter in the southern
highlands of Mars, had already hoisted material from far underground, and then the rim of
Huygens, containing the lifted material, was drilled into by a smaller, unnamed cratering event.

Observations in the high-resolution mode of the Compact Reconnaissance Imaging Spectrometer
for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter show spectral characteristics
of calcium or iron carbonate at this site. Detections of clay minerals in lower-resolution mapping
mode by CRISM had prompted closer examination with the spectrometer, and the carbonates are
found near the clay minerals. Both types of minerals typically form in wet environments.

The occurrence of this type of carbonate in association with the largest impact features suggests
that it was buried by a few kilometers (or miles) of younger rocks, possibly including volcanic
flows and fragmented material ejected from other, nearby impacts.

These findings reinforce a report by other researchers five months ago identifying the same types
of carbonate and clay minerals from CRISM observation of a site about 1,000 kilometers (600
miles) away. At that site, a meteor impact has exposed rocks from deep underground, inside
Leighton crater. In their report of that discovery, Joseph Michalski of the Planetary Science
Institute, Tucson, Ariz., and Paul Niles of NASA Johnson Space Center, Houston, proposed that
the carbonates at Leighton "might be only a small part of a much more extensive ancient
sedimentary record that has been buried by volcanic resurfacing and impact ejecta."

Carbonates found in rocks elsewhere on Mars, from orbit and by NASA's Spirit rover, are rich in
magnesium. Those could form from reaction of volcanic deposits with moisture, Wray said. "The
broader compositional range we're seeing that includes iron-rich and calcium-rich carbonates
couldn't form as easily from just a little bit of water reacting with igneous rocks. Calcium
carbonate is what you typically find on Earth's ocean and lake floors."

He said the carbonates at Huygens and Leighton "fit what would be expected from atmospheric
carbon dioxide interacting with ancient bodies of water on Mars." Key additional evidence
would be to find similar deposits in other regions of Mars. A hunting guide for that search is the
CRISM low-resolution mapping, which has covered about three-fourths of the planet and
revealed clay-mineral deposits at thousands of locations.

"A dramatic change in atmospheric density remains one of the most intriguing possibilities about
early Mars," said Mars Reconnaissance Orbiter Project Scientist Richard Zurek, of NASA's Jet
Propulsion Laboratory, Pasadena, Calif. "Increasing evidence for liquid water on the surface of
ancient Mars for extended periods continues to suggest that the atmosphere used to be much
thicker."

Carbon dioxide makes up nearly all of today's Martian air and likely was most of a thicker early
atmosphere, too. In today's thin, cold atmosphere, liquid water quickly freezes or boils away.

What became of that carbon dioxide? NASA will launch the Mars Atmosphere and Volatile
Evolution Mission (MAVEN) in 2013 to investigate processes that could have stripped the gas
from the top of the atmosphere into interplanetary space. Meanwhile, CRISM and other
instruments now in orbit continue to look for evidence that some of the carbon dioxide in that
ancient atmosphere was removed, in the presence of liquid water, by formation of carbonate
minerals now buried far beneath the present surface.

The Johns Hopkins University Applied Physics Laboratory, Laurel, Md., provided and operates
CRISM, one of six instruments on the Mars Reconnaissance Orbiter. JPL, a division of the
California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter
project and the Mars Exploration Program for the NASA Science Mission Directorate,
Washington. For more about CRISM, see http://crism.jhuapl.edu . For more about the Mars
Reconnaissance Orbiter, visit http://www.nasa.gov/mro .

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