NASA Study of Clays Suggests Watery Mars Underground

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Guy Webster 818-354-6278
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Dwayne Brown 202-358-1726
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News release: 2011-337 Nov. 2, 2011

NASA Study of Clays Suggests Watery Mars Underground

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-337&cid=release_2011-337

PASADENA, Calif. -- A new NASA study suggests if life ever existed on Mars, the longest lasting
habitats were most likely below the Red Planet's surface.

A new interpretation of years of mineral-mapping data, from more than 350 sites on Mars examined
by European and NASA orbiters, suggests Martian environments with abundant liquid water on the
surface existed only during short episodes. These episodes occurred toward the end of a period of
hundreds of millions of years during which warm water interacted with subsurface rocks. This has
implications about whether life existed on Mars and how the Martian atmosphere has changed.

"The types of clay minerals that formed in the shallow subsurface are all over Mars," said John
Mustard, professor at Brown University in Providence, R.I. Mustard is a co-author of the study in the
journal Nature. "The types that formed on the surface are found at very limited locations and are quite
rare."

Discovery of clay minerals on Mars in 2005 indicated the planet once hosted warm, wet conditions. If
those conditions existed on the surface for a long era, the planet would have needed a much thicker
atmosphere than it has now to keep the water from evaporating or freezing. Researchers have sought
evidence of processes that could cause a thick atmosphere to be lost over time.

This new study supports an alternative hypothesis that persistent warm water was confined to the
subsurface and many erosional features were carved during brief periods when liquid water was
stable at the surface.

"If surface habitats were short-term, that doesn't mean we should be glum about prospects for life on
Mars, but it says something about what type of environment we might want to look in," said the
report's lead author, Bethany Ehlmann, assistant professor at the California Institute of Technology,
Pasadena, and scientist at NASA's Jet Propulsion Laboratory, also in Pasadena. "The most stable
Mars habitats over long durations appear to have been in the subsurface. On Earth, underground
geothermal environments have active ecosystems."

The discovery of clay minerals by the OMEGA spectrometer on the European Space Agency's Mars
Express orbiter added to earlier evidence of liquid Martian water. Clays form from the interaction of
water with rock. Different types of clay minerals result from different types of wet conditions.

During the past five years, researchers used OMEGA and NASA's Compact Reconnaissance Imaging
Spectrometer, or CRISM, instrument on the Mars Reconnaissance Orbiter to identify clay minerals at
thousands of locations on Mars. Clay minerals that form where the ratio of water interacting with
rock is small generally retain the same chemical elements as those found in the original volcanic
rocks later altered by the water.

The study interprets this to be the case for most terrains on Mars with iron and magnesium clays. In
contrast, surface environments with higher ratios of water to rock can alter rocks further. Soluble
elements are carried off by water, and different aluminum-rich clays form.

Another clue is detection of a mineral called prehnite. It forms at temperatures above about 400
degrees Fahrenheit (about 200 degrees Celsius). These temperatures are typical of underground
hydrothermal environments rather than surface waters.

"Our interpretation is a shift from thinking that the warm, wet environment was mostly at the surface
to thinking it was mostly in the subsurface, with limited exceptions," said Scott Murchie of Johns
Hopkins University Applied Physics Laboratory in Laurel, Md., a co-author of the report and
principal investigator for CRISM.

One of the exceptions may be Gale Crater, the site targeted by NASA's Mars Science Laboratory
mission. Launching this year, the mission's Curiosity rover will land and investigate layers that
contain clay and sulfate minerals.

NASA's Mars Atmosphere and Volatile Evolution Mission, or MAVEN, in development for a 2013
launch, may provide evidence for or against this new interpretation of the Red Planet's environmental
history. The report predicts MAVEN findings consistent with the atmosphere not having been thick
enough to provide warm, wet surface conditions for a prolonged period.

JPL, a division of Caltech, manages the Mars Reconnaissance Orbiter for NASA's Science Mission
Directorate in Washington. APL provided and operates CRISM. For more information about the
Mars Reconnaissance Orbiter, visit: http://www.nasa.gov/mro and http://mars.jpl.nasa.gov/mro .

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