NASA's Opportunity rover is slowly but surely hauling
itself out of a vast Martian crater after nearly a year plumbing the interior
for secrets of the red planet's ancient past.
Opportunity will take the same route it used to enter
Victoria crater on Sept. 11, 2007, after a year of scouting
from the rim. Engineers want the rover to make a graceful exit after seeing
an electric current spike in its left front wheel — a reminder of a similar
spike that occurred when its robotic twin Spirit lost use of a front right
wheel in 2006.
"If Opportunity were driving with only
five wheels, like Spirit, it probably would never get out of Victoria
Crater," said Bill Nelson, a rover mission manager at the Jet Propulsion
Laboratory (JPL) in Pasadena, Calif. "We also know from experience with
Spirit that if Opportunity were to lose the use of a wheel after it
is out on the level ground, mobility should not be a problem."
The rover drove close to the base
of a cliff that makes up part of the crater rim, called "Cape
Verde," and snapped detailed images of rock layers reaching 20 feet (6
meters) tall.
Opportunity's samples of the layers inside Victoria
crater suggest that the wind-blown sediments later met the influence of
groundwater sometime in the ancient past. The crater itself stretches half a
mile (800 meters) in diameter and is deeper than any previously seen by the
rover.
"The patterns broadly resemble what we saw at the
smaller craters Opportunity explored earlier," said longtime rover
science team planner Scott McLennan of the State University of New York, Stony
Brook. "By looking deeper into the layering, we are looking farther back
in time."
Neither Opportunity nor Spirit has escaped the ravages of
time and exposure, despite working far beyond the intended 90-day
lifespan. Opportunity currently drives with its robotic arm out of stowed
position, in case a worn shoulder motor stops working and keeps the arm locked
in storage.
Opportunity is now gearing up to check on some fist-size
and larger rocks that scattered across the Martian plains after huge objects
blasted craters deeper than Victoria in the surface.
"We've done everything we entered Victoria Crater to
do and more," said Bruce Banerdt, project scientist for the rovers at JPL.
Spirit has also woken up from its winter hibernation on
Mars, but will not move from its current haven until enough the available solar
energy reaches increases within a few months. That rover continues to work on
its masterpiece, full-circle color panorama while facing the sun from the north
edge of the "Home Plate" plateau.
Spirit will eventually head south of Home Plate to
examine some bright, silica-rich soil that it discovered last year — possible
evidence of the effects of hot water.
The rovers originally landed on Mars in January 2004.
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