Spirit Checks "Columbia Hills" On Mars
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 (CA) "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 (NY), 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
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."