Explosions
and falling rock once peppered the Martian hills that NASA's Mars rover Spirit
currently calls home, astronomers said Tuesday.
Spirit,
currently scaling Husband Hill above its Gusev Crater landing site, has found
evidence of an explosive period in the region's history, in which volcanoes or
a massive impact showered the land with debris and possibly unearthed magma.
Whether they were volcanic
or impact explosions, however, is not yet known.
"Earlier in
its history, this part of Gusev Crater was a violent place," said Steven
Squyres, lead scientist from Cornell
University for the Mars
Exploration Rover (MER) mission. "There were explosions going and there was
stuff raining from the sky, and some of it was altered to a significant degree by
a fairly modest size of water."
Squyres and
his fellow rover team members announced the find, which is based on a trio of
rock outcrops observed by Spirit's cameras, during a Tuesday press conference
at an American Geophysical Union meeting in New Orleans, Louisiana.
"Really, for
the first time since the start of the Spirit mission, we've got the kind of geology
we can sink our teeth into," Squyres said. "The last six weeks, I'd say, have
probably been the most productive of the whole Spirit mission."
Spirit's
sister rover Opportunity has also made progress, though not altogether scientific,
at its Meridiani Planum. The rover is slowly but surely inching its way out of
a deep
sand dune, though mission managers don't expect to free the robot for
another few weeks.
The
secret's in the rocks
It took the
Spirit rover months to clamber up Husband Hill's steep, slippery side, during
which time the robot found little to suggest the region differed from the
volcanic rock remains scattered across the rest of Gusev Crater.
But now
halfway up Husband, after studying three rock outcrops, researchers are telling
a different story.
"All of a
sudden, we have geologic structure...everything changed," Squyres said. "It was
nothing more than you had to look at it from a different angle."
Analysis by
Spirit of rock outcrops known as "Larry's Lookout," "Methuselah" and "Jibsheet"
contained signs of the Gusev's tumultuous past, researchers said.
"Their
chemical composition is very distinct from what we found out on the plains,"
said rover science team member Richard Morris, of NASA's Johnson Space Center
in Houston, adding that there are signs of the mineral ilmenite - which is
often formed in magma. "This is the first appearance of this mineral we've
seen."
While the
rocks around Spirit share some compositional traits, the amount of weathering
due to water differs among the outcrops, as do their textures. At "Methuselah,"
for example, astronomers found the finest rock layers seen by Spirit to date,
while "Jibsheet" sported a bulbous, globular look.
"Gusev has
certainly turned out to be different than we expected it to be," Squyres said,
adding that he still believes that the crater was once the watery lake suggested
by orbital photographs.
The rocks
of the Columbia Hill chain, which includes Husband Hill, may completely predate
that Gusev lake, rising like an island above the plains, Squyres added.
Opportunity
ekes forward
While
Spirit continues to explore Husband Hill, its robotic twin Opportunity is
slowly but surely crawling
out of a sandy quagmire on the other side of Mars.
The rover
has moved about 10 inches (27 centimeters) - though its wheels turned enough to
travel 157 feet (48 meters) - which mission controllers say is
good progress. [An animation of Opportunity's wheel-spinning is available by
clicking here.]
"We're only
traveling about half a percent of what we're commanding," explained Jim
Erickson, rover project manager at NASA's Jet Propulsion Laboratory. "So it's a
very low number, but very consistent."
At the
current rate, it may be two more weeks before Opportunity once again reaches
safe ground, Erickson added.
Opportunity
is currently stuck in the outskirts of a region known as the "etched terrain"
which contains - scientists hope - exposed bedrock that could shed more light
on water's role in the history of Meridiani Planum. Astronomers know that the region
was once awash
with the liquid stuff.
"We're
learning that's it's a tough place to do business," Squyres said of the area.
Now well
past the one-year
mark, NASA's Spirit and Opportunity rovers are still going strong.
"We're
still trying to decide exactly how long they'll go by running them until they
wear out," Erickson said. "We just don't know how long these things are going
to last."
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