When it
comes to Mars missions, NASA's twin rovers Spirit and Opportunity seem to be
the robots that never quit.
The two plucky probes were each built
for a 90-day romp across the Martian surface, a mission that began when Spirit
bounced to a stop on the planet's expansive Gusev Crater five years ago today.
Opportunity touched down on the other side of Mars a few weeks later and now - after
half a decade - both rovers are still
exploring the red planet after surviving more than 20 times their planned
lifetime.
"The American taxpayer was told three months for each
rover was the prime mission plan," said Ed Weiler, NASA's associate
administrator for science missions at the agency's Washington, D.C.,
headquarters, in a statement. "The twins have worked almost 20 times that
long. That's an extraordinary return of investment in these challenging
budgetary times."
The rovers reportedly cost about $20 million to operate each
year since their 2004 arrivals on Mars.
Roving Mars
Spirit set
down at Gusev Crater on Jan. 3 at 11:35 p.m. EST (8:35 p.m. PST), where it
overcame initial computer glitches and went on to scale nearby hills and brave
the frigid Martian winter year after year.
Opportunity
bounced to a stop inside what scientists later dubbed Eagle crater just after
midnight (EST) Jan. 25 in an interplanetary hole-in-one on the vast Martian
plains of Meridiani Planum. Since then, the rover has spotted a Martian
meteorite, visited the heat shield cast off during its landing and explored
ever larger craters as it makes
it way toward Endeavour, a monster crater 14 miles (22 km) across.
"We keep setting the bar higher for what these rovers can
do," said Frank Hartman, a rover driver at NASA's Jet Propulsion
Laboratory in Pasadena, Calif., which manages the mission. "Once it seemed
like a crazy idea to go to Endeavour, but now we're doing it."
Both rovers
have weathered glitches from old age, with Opportunity digging its way out of a
Martian sand dune that threatened to halt its red planet exploration. Since
their mission began, Spirit and Opportunity have returned a veritable feast of
information on the composition of Mars' surface and history of water at their
local landing sites.
Altogether,
the rovers have driven across more than 13 miles (21 km) of Martian terrain,
taken some 250,000 photographs and beamed more than 36 gigabytes of data to
Earth. They've also been the stars of film and television
documentaries lauding their unexpected long life.
"These rovers are incredibly resilient considering the
extreme environment the hardware experiences every day," said John Callas,
NASA's rover project manager at JPL. "We realize that a major rover
component on either vehicle could fail at any time and end a mission with no
advance notice, but on the other hand, we could accomplish the equivalent
duration of four more prime missions on each rover in the year ahead."
After third winter, new science ahead
Spirit came close to a
chilly demise this year as power levels dwindled in the dim Martian winter,
mission managers said. But the rover has bounced back after surviving the
season, its third winter in the planet's southern hemisphere, which ended in
December.
"This last winter was a squeaker for Spirit,"
Callas said. "We just made it through."
Scientists plan to send Spirit to a pair of interesting
spots about 600 feet (183 meters) away from its current perch atop a rocky plateau
called Home Plate, which the rover has been studying since 2006. One target is
a mound that may hold the key to determining if Home Plate is the remains of a
larger expanse of volcanic material. The other is a depression called Goddard,
an immense pit the size of a house.
"Goddard doesn't look like an impact crater," said
Steve Squyres, principal investigator for the rover science instruments at Cornell
University, in Ithaca, New York. "We suspect it might be a volcanic
explosion crater, and that's something we haven't seen before."
Meanwhile,
Spirit's twin Opportunity is chugging along toward Endeavour Crater. The crater
is 20 times larger than Opportunity's last destination, Victoria Crater, which
commanded the rover's attention for nearly two years. The new target sits just
seven miles (12 km) from Victoria, but Opportunity must drive much farther to
zigzag around obstacles and inspect loose rocks along the way.
"This has turned into humanity's first overland expedition
on another planet," said Squyres. "When people look back on this period of Mars
exploration decades from now, Spirit and Opportunity may be considered most
significant not for the science they accomplished, but for the first time we
truly went exploring across the surface of Mars."
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