[meteorite-list] NASA Study Of Clay Minerals Suggests Watery Martian Underground

[Ron Baalke]

Nov. 2, 2011

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: 11-369

NASA STUDY OF CLAY MINERALS SUGGESTS WATERY MARTIAN UNDERGROUND

WASHINGTON -- 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 hundreds of millions of years during which warm water 
interacted with subsurface rocks. This has implications about whether 
life existed on Mars and how its 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 and scientist at NASA's Jet Propulsion 
Laboratory 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 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 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 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  
	
-end-