March
26, 2009: In January 2004, NASA landed two identical
robotic rovers named Spirit and Opportunity on the surface
of Mars. The twins were primed for a brief 3-month mission
to tell us a story of water and possibly life itself in the
planet's past. More than five years later, the dynamic duo
are still roving the Red Planet, engaged in a saga of overachievement
that has transformed Mars exploration.
"Spirit
and Opportunity helped invent a whole new discipline -- robotic
field science," says Steve Squyres, principal investigator
for the Mars Exploration Rover Mission. "They've taught
us how to organize large teams of scientists and engineers
to operate robotic rovers on a distant planet. We all had
to learn to work together effectively year after year to squeeze
the most possible science from the rovers."
Right:
Opportunity on Mars. [more]
The
teams are still squeezing.
Among
the remarkable findings from these solar-powered robots over
the half-decade: Mars wasn't always as cold and dry as it
is today. Maybe it didn't look like a set for The Sound
of Music, but it had water and was warm enough for life.
Mars
Exploration Mission team members have also learned the perils
of maneuvering robotic rovers located a hundred million kilometers
away. They've gotten the vehicles stuck more than once. "We
now know how to negotiate sand dunes and piles of rocks,"
says Squyres, "and perhaps more importantly – how to
avoid them. We've translated five years of experience into
new and improved maps and driving software that will help
us in the remainder of our mission, and will also help future
rovers."
Hopeful
planners are already setting future operations for the twins,
assuming the pair will continue to plow ahead but acknowledging
that one or both of the rovers could fail at any time. After
all, these robots aren't exactly spring chickens. Spirit has
been driving backwards since one of its wheels jammed in 2006,
and a broken electrical wire has reduced movement of Opportunity's
robotic arm.
Provided
the twins hold up a while longer, here are the latest plans:
Opportunity,
"the lucky vehicle since day 1" according to Squyres,
has been crater-hopping since the beginning of the mission
and is now heading south to the largest crater yet. The Endeavor
crater is 20 km in diameter and 100s of meters deep.
"We'll
have to double the odometer reading on a five year old vehicle
to get there," says Squyres. "And it will take at
least two years to reach it. [100 meters per day is an average
day for Opportunity.] It'll be a long march across the plains,
but it will be well worth it. The deeper the crater the older
the history of Mars we can look at."
Above:
"The long march." Opportunity looks back on its
own tire tracks en route to Endeavor crater. [more]
Ray
Arvidson, deputy principal investigator, elaborates: "Endeavor
is an intriguing target because the rocks close to it look
different from the ones surrounding the other craters Opportunity
has visited. Part of Endeavor crater's rim is sticking up
– Mars' ancient bedrock exposed -- and rocks nearby may be
suggestive of acidic lakes on Mars' surface billions of years
ago."
And
what about the other twin?
"Spirit
is the more challenging rover to operate," says Squyres.
"There's not as much wind at its location to clean the
solar arrays, and that affects the vehicle's power. Also,
Spirit has to travel a more challenging terrain. The rocks
and loose sand at Spirit's location are treacherous. Of course,
to top it all off, Spirit is driving backwards.
Right:
Sticky dust on Spirit's solar panels has reduced power to
the rover. [more]
Luckily,
Spirit's landing site features a compact geology with enormous
diversity and variability in a small area."
Spirit
is now creeping steadily along a route to von Braun, an interesting
looking mesa-shaped cap-rock that stands only about 250 meters
away but will take months to reach. Then Spirit will head
to a 30-meter diameter pit that may be a volcanic explosion
crater -- and perhaps a location for hydrothermal activity.
"Because
of the geology of its surroundings, Spirit specializes in
looking for evidence in the rock record of water-charged explosive
volcanism," says Arvidson. "Such areas could have
once supported life."
"Home
Plate, where Spirit spent the winter, is a volcanic structure
eroded down so we can see the layers," explains Arvidson.
"And we think von Braun and the neighboring Goddard structure
may be made of the same stuff."
The
Mars Exploration Team members have high hopes for the rovers
to achieve all these ambitious goals but are mindful of the
twins' limitations.
"We
have no way of knowing what the future holds for the rovers
at this point," says Squyres. "The mission could
easily end tomorrow. But, the miracle could continue."
Below:
Sunset on Mars, recorded by Spirit in 2005. [more]
Arvidson
recalls the day, over five years ago, when Spirit first touched
down on the red planet.
“I
was on a plane on my way back from Hawaii, headed to the Los
Angeles airport, when Spirit was due to land. I just had to
know if the rover had made it, so I asked the pilot to radio
ahead to air traffic controllers and find out if Spirit had
landed safely. I was overjoyed when he did so and confirmed
that Spirit was sitting on Mars' surface, ready to go!"
Spirit
is still going, Opportunity is still going, and Arvidson is
still overjoyed.
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Author: Dauna Coulter
| Editor: Dr.
Tony Phillips | Credit: Science@NASA
|