Bedrock in Mars' Gusev Crater Hints at Watery Past
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'
Image above:This approximate true-color image taken by Spirit shows a rock outcrop dubbed "Longhorn," and behind it, the sweeping plains of Gusev Crater. On the horizon, the rim of Gusev Crater is clearly visible. + Click for full image. Image credit: NASA/JPL/Cornell
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
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
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."
Images and additional
information about the rovers are available from JPL at
and from Cornell University at
NASA's Jet Propulsion Laboratory
NASA Headquarters, Washington