Two robots the
size of golf carts were given 90 days to squeeze as much science as possible
from the barren, dust-swept terrain of Mars. After that, scientists expected
nothing more from them than death.
Nearly four
years after their warranties expired, however, the Mars
Explorations Rovers (MERs) "Spirit" and "Opportunity" continue
to play productively in the red dirt.
Spirit celebrates
its fourth anniversary of Martian work on Jan. 4, the day it landed in 2004, followed
by Opportunity on Jan. 25. Those four Earth years since landing convert to 2.25
Martian years, or 1,422 Martian days called "sols."
"We
never thought we'd still be driving these robots all over Mars," said Mark Lemmon, a planetary scientist at Texas A&M University and member of the rover science team. "We
joked about driving Opportunity into Victoria Crater, but now we're there, and
we're looking at doing even more science. Each day they still work is an amazing one."
Happy
anniversary
Since the
rovers bounced onto Mars' surface, they have collectively driven more than 11.8
miles (19.1 kilometers) and snapped more than 210,000 images. That's roughly 55
standard DVD movies worth of uncompressed data.
Scientists
have used this information through the years to crank out more than 100 studies
about the planet's geologic past "with many more in progress," Lemmon
said.
"It's
been a great year for the rovers and we're getting deeper into Martian history
than we've ... done before," Lemmon said. "These robots have
entirely changed the way we view Mars."
Those views
include support for the existence of water
on Mars, at least in the past, in the form of silica and meteorites.
In addition
to that evidence, the year 2007 inflicted a global dust storm on the rovers. Although
indirect sunlight powered the rovers through the dusty conditions, more than 96
percent of direct sunlight to their solar panels was filtered out.
"It
was scary there for a while," Lemmon said of the low-light conditions that
nearly drove the rovers to a permanent standstill.
Despite the
nerve-wracking task of keeping both rovers power-positive — and their electronic
circuits from snapping in the Martian cold — Lemmon explained that new science
is still trickling out as a result of the weather event.
"The
Mars orbiters looked down on the dust storm when it happened, but they didn't
measure changes on the ground like the rovers did," he said. "The
rovers are really helping us to better understand these storms."
Winter
parking spot
Now that the
dusty, five- to six-month Martian summer is waning and winter is creeping up, earthly
operators have pinned down an over-winter parking spot for Spirit.
The rover
suffered software glitches early in the mission, and now drives backward as its
front right wheel is indefinitely stuck. Making matters worse is the literal
fallout from the recent dust storm.
"Right
now, we're working with the dustiest rover we've ever had," Lemmon said,
who does not expect whirling
dust devils to clean off the rover's coated solar panels any time soon.
"As a result, we pretty much consider Spirit parked."
Lemmon said
Opportunity, however, is in good shape to continue exploring and the team has
no definitive date for parking the adventurous machine.
"Opportunity has much cleaner [solar panels] than Spirit," Lemmon said, "so
there's no discussion of racing it to a north-facing slope for the
winter."
Scientists used
the north-facing-slope trick in the past, which helps maximize direct sunlight
to the rover's solar panels during the dim Martian winter.
While Opportunity continues to maneuver around Victoria Crater, Spirit is presently resting on a
slope of Home Plate — a layered outcrop of rock in the shape of a baseball home
plate. "It'll stay in one place for a long time, but we'll still be able
to do some science," Lemmon said.
That science
includes watching the sky for water-crystal clouds and taking atmospheric
measurements, but the rover may also witness a potential
asteroid impact later this month.
"I'm not optimistic for the rovers seeing anything ...
[but] we have some hope of seeing the impact cloud as it disperses around the
planet," Lemmon said. "I like the thought of a birthday present from
Mars. It'll certainly contribute more excitement to the mission."
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