NASA Mars Rover Finds Mineral Vein Deposited by Water


WASHINGTON -- 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,
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), 16 to 20 inches 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 have 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 minerals combined with sulfur either leached from the
rocks or introduced as volcanic gas, and 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.

"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."

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.

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:



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