NASA Mars Rover Finds Mineral Vein Deposited by Water

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Guy Webster 818-354-6278
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Steve Cole 202-358-0918
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News release: 2011-377 Dec. 7, 2011

NASA Mars Rover Finds Mineral Vein Deposited by Water

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-377&cid=release_2011-377

PASADENA, Calif. -- NASA's Mars Exploration Rover Opportunity has found bright veins of a
mineral, apparently gypsum, deposited by water. Analysis of the vein will help improve understanding
of the history of wet environments on Mars.

"This tells a slam-dunk story that water flowed through underground fractures in the rock," said Steve
Squyres of Cornell University, Ithaca, N.Y., principal investigator for Opportunity. "This stuff is a fairly
pure chemical deposit that formed in place right where we see it. That can't be said for other gypsum
seen on Mars or for other water-related minerals Opportunity has found. It's not uncommon on Earth,
but on Mars, it's the kind of thing that makes geologists jump out of their chairs."

The latest findings by Opportunity were presented Wednesday at the American Geophysical Union's
conference in San Francisco.

The vein examined most closely by Opportunity is about the width of a human thumb (0.4 to 0.8 inch, or
1 to 2 centimeters), 16 to 20 inches (40 to 50 centimeters) long, and protrudes slightly higher than the
bedrock on either side of it. Observations by the durable rover reveal this vein and others like it within
an apron surrounding a segment of the rim of Endeavour Crater. None like it were seen in the 20 miles
(33 kilometers) of crater-pocked plains that Opportunity explored for 90 months before it reached
Endeavour, nor in the higher ground of the rim.

Last month, researchers used the Microscopic Imager and Alpha Particle X-ray Spectrometer on the
rover's arm and multiple filters of the Panoramic Camera on the rover's mast to examine the vein, which
is informally named "Homestake." The spectrometer identified plentiful calcium and sulfur, in a ratio
pointing to relatively pure calcium sulfate.

Calcium sulfate can exist in many forms, varying by how much water is bound into the minerals'
crystalline structure. The multi-filter data from the camera suggest gypsum, a hydrated calcium sulfate.
On Earth, gypsum is used for making drywall and plaster of Paris.
Observations from orbit had detected gypsum on Mars previously. A dune field of windblown gypsum
on far northern Mars resembles the glistening gypsum dunes in White Sands National Monument in
New Mexico.

"It is a mystery where the gypsum sand on northern Mars comes from," said Opportunity science-team
member Benton Clark of the Space Science Institute in Boulder, Colo. "At Homestake, we see the
mineral right where it formed. It will be important to see if there are deposits like this in other areas of
Mars."

The Homestake deposit, whether gypsum or another form of calcium sulfate, likely formed from water
dissolving calcium out of volcanic rocks. The calcium combined with sulfur that was either leached
from the rocks or introduced as volcanic gas, and it was deposited as calcium sulfate into an
underground fracture that later became exposed at the surface.

Throughout Opportunity's long traverse across Mars' Meridiani plain, the rover has driven over bedrock
composed of magnesium, iron and calcium sulfate minerals that also indicate a wet environment billions
of years ago. The highly concentrated calcium sulfate at Homestake could have been produced in
conditions more neutral than the harshly acidic conditions indicated by the other sulfate deposits
observed by Opportunity.

"It could have formed in a different type of water environment, one more hospitable for a larger variety
of living organisms," Clark said.

Homestake and similar-looking veins appear in a zone where the sulfate-rich sedimentary bedrock of the
plains meets older, volcanic bedrock exposed at the rim of Endeavour. That location may offer a clue
about their origin.

Opportunity and its rover twin, Spirit, completed their three-month prime missions on Mars in April
2004. Both rovers continued for years of extended missions and made important discoveries about wet
environments on ancient Mars that may have been favorable for supporting microbial life. Spirit stopped
communicating in 2010. Opportunity continues exploring, currently heading to a sun-facing slope on the
northern end of the Endeavour rim fragment called "Cape York" to keep its solar panels at a favorable
angle during the mission's fifth Martian winter.

"We want to understand why these veins are in the apron but not out on the plains," said the mission's
deputy principal investigator, Ray Arvidson, of Washington University in St. Louis. "The answer may
be that rising groundwater coming from the ancient crust moved through material adjacent to Cape York
and deposited gypsum, because this material would be relatively insoluble compared with either
magnesium or iron sulfates."

NASA launched the next-generation Mars rover, the car-sized Curiosity, on Nov. 26. It is slated for
arrival at the planet's Gale Crater in August 2012. NASA's Jet Propulsion Laboratory, a division of the
California Institute of Technology in Pasadena, manages the Mars Exploration Rover Project for the
NASA Science Mission Directorate in Washington. For more information about the rovers, visit
http://www.nasa.gov/rovers and http://marsrovers.jpl.nasa.gov . You can follow the project on
Twitter at http://twitter.com/MarsRovers and on Facebook at http://www.facebook.com/marsrovers
.
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