Press Release

NASA Spirit Rover: Bedrock in Mars’ Gusev Crater Hints at Watery Past

By SpaceRef Editor
August 18, 2004
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NASA Spirit Rover: Bedrock in Mars’ Gusev Crater Hints at Watery Past
08.18.04.mars.jpg

Now that NASA’s Mars Exploration Rover Spirit is finally examining
bedrock in the “Columbia Hills,” it is finding evidence that water
thoroughly altered some rocks in Mars’ Gusev Crater.

Spirit and its twin, Opportunity, completed successful three-month
primary missions on Mars in April and are returning bonus results
during extended missions. They remain in good health though beginning
to show signs of wear.

On Opportunity, a tool for exposing the insides of rocks stopped
working Sunday, but engineers are optimistic that the most likely
diagnosis is a problem that can be fixed soon. “It looks like there’s
a pebble trapped between the cutting heads of the rock abrasion tool,”
said Chris Salvo, rover mission manager at NASA’s Jet Propulsion
Laboratory, Pasadena, Calif. “We think we can treat it by turning the
heads in reverse, but we are still evaluating the best approach to
remedy the situation. There are several options available to us.”

Opportunity originally landed right beside exposed bedrock and
promptly found evidence there for an ancient body of saltwater. On the
other hand, it took Spirit half a year of driving across a martian
plain to reach bedrock in Gusev Crater. Now, Spirit’s initial
inspection of an outcrop called “Clovis” on a hill about 9 meters (30
feet) above the plain suggests that water may once have been active at
Gusev.

“We have evidence that interaction with liquid water changed the
composition of this rock,” said Dr. Steve Squyres of Cornell
University, Ithaca, N.Y., principal investigator for the science
instruments on both rovers. “This is different from the rocks out on
the plain, where we saw coatings and veins apparently due to effects
of a small amount of water. Here, we have a more thorough, deeper
alteration, suggesting much more water.”

Squyres said, “To really understand the conditions that altered
Clovis, we’d like to know what it was like before the alteration. We
have the ‘after.’ Now we want the ‘before.’ If we’re lucky, there may
be rocks nearby that will give us that.”

Dr. Doug Ming, a rover science team member from NASA’s Johnson Space
Center, Houston, said indications of water affecting Clovis come from
analyzing the rock’s surface and interior with Spirit’s alpha particle
X-ray spectrometer and finding relatively high levels of bromine,
sulfur and chlorine inside the rock. He said, “This is also a very
soft rock, not like the basaltic rocks seen back on the plains of
Gusev Crater. It appears to be highly altered.”

Rover team members described the golf-cart-sized robots’ status and
recent findings in a briefing at JPL today.

Opportunity has completed a transect through layers of rock exposed in
the southern inner slope of stadium-sized “Endurance Crater.” The
rocks examined range from outcrops near the rim down through
progressively older and older layers to the lowest accessible outcrop,
called “Axel Heiberg” after a Canadian Arctic island. “We found
different compositions in different layers,” said Dr. Ralf Gellert, of
Max-Planck-Institut fur Chemie, Mainz, Germany. Chlorine concentration
increased up to threefold in middle layers. Magnesium and sulfur
declined nearly in parallel with each other in older layers,
suggesting those two elements may have been dissolved and removed by
water.

Small, gray stone spheres nicknamed “blueberries” are plentiful in
Endurance just as they were at Opportunity’s smaller landing-site
crater, “Eagle.” Pictures from the rover’s microscopic imager show a
new variation on the blueberries throughout a reddish-tan slab called
“Bylot” in the Axel Heiberg outcrop. “They’re rougher textured, they
vary more in size, and they’re the color of the rock, instead of
gray,” said Zoe Learner, a science team collaborator from Cornell.
“We’ve noticed that in some cases where these are eroding, you can see
a regular blueberry or a berry fragment inside.” One possibility is
that a water-related process has added a coarser outer layer to the
blueberries, she said, adding, “It’s still really a mystery.”

JPL, a division of the California Institute of Technology in Pasadena,
manages the Mars Exploration Rover project for NASA’s Science Mission
Directorate, Washington. Images and additional information about the
project are available from JPL at http://marsrovers.jpl.nasa.gov and
from Cornell University at http://athena.cornell.edu .

SpaceRef staff editor.