[meteorite-list] Opportunity Rover Finds Strong Evidence Meridiani Planum Was Wet

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:32:45 2004
Message-ID: <200403022102.NAA29751_at_zagami.jpl.nasa.gov>

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov

Guy Webster (818) 354-5011
Jet Propulsion Laboratory, Pasadena, Calif.

Donald Savage (202) 358-1547
NASA Headquarters, Washington March 2, 2004
     
NEWS RELEASE: 2004-074
     
OPPORTUNITY ROVER FINDS STRONG EVIDENCE MERIDIANI PLANUM WAS WET

Scientists have concluded the part of Mars that NASA's Opportunity
rover is exploring was soaking wet in the past.

Evidence the rover found in a rock outcrop led scientists to the
conclusion. Clues from the rocks' composition, such as the presence of
sulfates, and the rocks' physical appearance, such as niches where
crystals grew, helped make the case for a watery history.

"Liquid water once flowed through these rocks. It changed their
texture, and it changed their chemistry," said Dr. Steve Squyres of
Cornell University, Ithaca, N.Y., principal investigator for the
science instruments on Opportunity and its twin, Spirit. "We've been
able to read the tell-tale clues the water left behind, giving us
confidence in that conclusion."

Dr. James Garvin, lead scientist for Mars and lunar exploration at
NASA Headquarters, Washington, said, "NASA launched the Mars
Exploration Rover mission specifically to check whether at least one
part of Mars ever had a persistently wet environment that could
possibly have been hospitable to life. Today we have strong evidence
for an exciting answer: Yes."

Opportunity has more work ahead. It will try to determine whether,
besides being exposed to water after they formed, the rocks may have
originally been laid down by minerals precipitating out of solution at
the bottom of a salty lake or sea.

The first views Opportunity sent of its landing site in Mars'
Meridiani Planum region five weeks ago delighted researchers at NASA's
Jet Propulsion Laboratory, Pasadena, Calif., because of the good
fortune to have the spacecraft arrive next to an exposed slice of
bedrock on the inner slope of a small crater.

 The robotic field geologist has spent most of the past three weeks
surveying the whole outcrop, and then turning back for close-up
inspection of selected portions. The rover found a very high
concentration of sulfur in the outcrop with its alpha particle X-ray
spectrometer, which identifies chemical elements in a sample.
"The chemical form of this sulfur appears to be in magnesium, iron or
other sulfate salts," said Dr. Benton Clark of Lockheed Martin Space
Systems, Denver. "Elements that can form chloride or even bromide
salts have also been detected."

At the same location, the rover's Moessbauer spectrometer, which
identifies iron-bearing minerals, detected a hydrated iron sulfate
mineral called jarosite. Germany provided both the alpha particle
X-ray spectrometer and the Moessbauer spectrometer. Opportunity's
miniature thermal emission spectrometer has also provided evidence for
sulfates.

On Earth, rocks with as much salt as this Mars rock either have formed
in water or, after formation, have been highly altered by long
exposures to water. Jarosite may point to the rock's wet history
having been in an acidic lake or an acidic hot springs environment.

The water evidence from the rocks' physical appearance comes in at
least three categories, said Dr. John Grotzinger, sedimentary
geologist from the Massachusetts Institute of Technology, Cambridge:
indentations called "vugs," spherules and crossbedding.

Pictures from the rover's panoramic camera and microscopic imager
reveal the target rock, dubbed "El Capitan," is thoroughly pocked with
indentations about a centimeter (0.4 inch) long and one-fourth or less
that wide, with apparently random orientations. This distinctive
texture is familiar to geologists as the sites where crystals of salt
minerals form within rocks that sit in briny water. When the crystals
later disappear, either by erosion or by dissolving in less-salty
water, the voids left behind are called vugs, and in this case they
conform to the geometry of possible former evaporite minerals.

Round particles the size of BBs are embedded in the outcrop. From
shape alone, these spherules might be formed from volcanic eruptions,
from lofting of molten droplets by a meteor impact, or from
accumulation of minerals coming out of solution inside a porous,
water-soaked rock. Opportunity's observations that the spherules are
not concentrated at particular layers in the outcrop weigh against a
volcanic or impact origin, but do not completely rule out those
origins.

Layers in the rock that lie at an angle to the main layers, a pattern
called crossbedding, can result from the action of wind or water.
Preliminary views by Opportunity hint the crossbedding bears hallmarks
of water action, such as the small scale of the crossbedding and
possible concave patterns formed by sinuous crestlines of underwater
ridges.

The images obtained to date are not adequate for a definitive answer.
So scientists plan to maneuver Opportunity closer to the features for
a better look. "We have tantalizing clues, and we're planning to
evaluate this possibility in the near future," Grotzinger said.

JPL, a division of the California Institute of Technology in Pasadena,
manages the Mars Exploration Rover project for NASA's Office of Space
Science, Washington.

For information about NASA and the Mars mission on the Internet, visit

http://www.nasa.gov

Images and additional information about the project are also
available on the Internet at:

http://marsrovers.jpl.nasa.gov

and

http://athena.cornell.edu

-end-
Received on Tue 02 Mar 2004 04:02:51 PM PST