NASA's Mars Rover Spirit Faces Circuitous Route
PASADENA, Calif. -- Loose soil piled against the northern edge of a low
plateau called "Home Plate" has blocked NASA's Mars Exploration Rover
Spirit from taking the shortest route toward its southward destinations
for the upcoming Martian summer and following winter.
The rover has begun a trek skirting at least partway around the plateau
instead of directly over it.
However, Spirit has also gotten a jump start on its summer science plans,
examining a silica-rich outcrop that adds information about a long-gone
environment that had hot water or steam. And even a circuitous route to the
destinations chosen for Spirit would be much shorter than the overland expedition
Spirit's twin, Opportunity, is making on the opposite side of Mars.
Both rovers landed on Mars in 2004 for what were originally planned as
three-month missions there.
Spirit spent 2008 on the northern edge of Home Plate, a flat-topped deposit
about the size of a baseball field, composed of hardened ash and rising about
1.5 meters (5 feet) above the ground around it. There, the north-facing tilt
positioned Spirit's solar arrays to catch enough sunshine for the rover to survive
the six-month-long Martian winter.
The scientists and engineers who operate the rovers chose as 2009 destinations a
steep mound called "Von Braun" and an irregular, 45-meter-wide (150-foot-wide) bowl
called "Goddard." These side-by-side features offer a promising area to examine while
energy is adequate during the Martian summer and also to provide the next north-facing
winter haven beginning in late 2009. Von Braun and Goddard intrigue scientists as sites
where Spirit may find more evidence about an explosive mix of water and volcanism in
the area's distant past. They are side-by-side, about 200 meters, or yards, south of
where Spirit is now.
It's mid-spring now in the southern hemisphere of Mars. The sun has climbed higher in
the sky over Spirit in recent weeks.
The rover team tried to drive Spirit onto Home Plate, heading south toward Von Braun
and Goddard. They tried this first from partway up the slope where the rover had spent
the winter. Only five of the six wheels on Spirit have been able to rotate since the
right-front wheel stopped working in 2006. With five-wheel drive, Spirit couldn't climb
the slope. In January and February, Spirit descended from Home Plate and drove eastward
about 15 meters (about 50 feet) toward a less steep on-ramp. Spinning wheels in loose soil
led the rover team to choose another of its options.
"Spirit could not make progress in the last two attempts to get up onto Home Plate," said
John Callas of NASA's Jet Propulsion Laboratory, Pasadena, Calif., project manager for both
rovers. "Alternatively, we are driving Spirit around Home Plate to the east. Spirit will
have to go around a couple of small ridges that extend to the northeast, and then see whether
a route east of Home Plate looks traversable. If that route proves not to be traversable, a
route around the west side of Home Plate is still an option."
During the drive eastward just north of Home Plate in January, Spirit stopped to use tools on
its robotic arm to examine a nodular, heavily eroded outcrop dubbed "Stapledon," which had caught
the eye of rover-team scientist Steve Ruff when he looked at images and infrared spectra Spirit
took from its winter position.
"It looked like the material east of Home Plate that we found to be rich in silica," said Ruff,
of Arizona State University, Tempe. "The silica story around Home Plate is the most important
finding of the Spirit mission so far with regard to habitability. Silica this concentrated forms
around hot springs or steam vents, and both of those are favorable environments for life on Earth."
Sure enough, Spirit's alpha particle X-ray spectrometer found Stapledon to be rich in silica, too.
"Now we have found silica on a second side of Home Plate, expanding the size of the environment
we know was affected by hot springs or steam vents," Ruff said. "The bigger this system, the more
water was involved, the more habitable this system may have been."
The contact measurement with the X-ray spectrometer also gave the team confidence in its ability
to identify silica-rich outcrops from a distance with the rover's thermal emission spectrometer,
despite some dust that has accumulated on a periscope mirror of that instrument. Researchers plan
to use Spirit's thermal emission spectrometer and panoramic camera to check for more silica-rich
outcrops on the route to Von Braun and Goddard. However, the team has set a priority to make good
progress toward those destinations. Winds cleaned some dust off Spirit's solar panels on Feb. 6 and
Feb. 14, resulting in a combined increase of about 20 percent in the amount of power available to the rover.
Opportunity, meanwhile, shows signs of increased friction in its right-front wheel. The team is
driving the rover backwards for a few sols, a technique that has helped in similar situations in the
past, apparently by redistributing lubricant in the wheel. Opportunity's major destination is Endeavour
Crater, about 22 kilometers (14 miles) in diameter and still about 12 kilometers (7 miles) away to the
southeast. Opportunity has been driving south instead of directly toward Endurance, to swing around
an area where loose soil appears deep enough to potentially entrap the rover.
JPL, a division of the California Institute of Technology, Pasadena, manages the Mars Exploration Rovers
for the NASA Science Mission Directorate, Washington. More information about the rovers is at http://www.nasa.gov/rovers
Media contact: Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif.