NASA's Spirit
rover currently exploring Mars completed one full swing around the Sun Monday,
giving researchers a year-long look at the Martian seasons.
"We feel
like, weather-wise, we've just about seen it all," said Sharon Laubach, the
rover's integrating sequence team chief, in a telephone interview. "We've gone
through all the seasons, we've survived Martian winter
and gone through conjunction...yes, we're having a party."
While both
Spirit and its robotic twin Opportunity hit the one Earth
year mark of their mission in January, researchers said the Nov. 21 Martian
anniversary holds far more significance for the long-lived rovers.
"It's a
big, important milestone," said Steve Squyres, principal investigator of the
rover's science mission at Cornell University in Ithaca, New York in an earlier
interview. "We'll have acquired an entire year's worth of observations."
One Mars year
is longer than Earth's (about 687 Earth days), with Spirit hitting its
anniversary on the 670th sol - or Martian day - of its mission. Spirit
has rolled across 3.3 miles (5.4 kilometers) of Martian terrain at its landing
site inside the planet's Gusev crater.
Opportunity
will complete its first Martian year exploring the plains of Meridiani Planum
on Dec. 11, mission scientists said. Both rovers touched
down on Mars in January 2004 on a primary mission that spanned 90 days.
Martian
weather
Spirit and
Opportunity are currently experiencing the final days of Martian summer and preparing
for the onset of autumn, mission managers said.
During its
first Martian year, Spirit found dust
devils swirling across the planet's landscape and frost settling on the its
surface, researchers said, adding that the fringes of a major dust storm may
have brushed
Opportunity last month.
"So the
planet, though it seems dead, does have a vibrant atmosphere," explained Amitabha
Ghosh, an atmospheric scientist and rover science team member with
Gaithersburg, Maryland's Tharsis, Inc.
Ghosh is
using the mast-mounted Miniature Thermal Emissions Spectrometer (Mini-TES)
aboard both rovers to study atmospheric changes depending on the Martian
season.
"There are
some really seasonal phenomena, like the dust devils," Squyres said.
Mars researchers
initially hoped to find many dust devils roaming across the Martian surface,
but had to wait until early
spring on the planet before the first whirlwinds were caught by Spirit's
cameras.
The
infrared Mini-TES instrument, which is also used by geologists to determine
Martian rock and soil minerals, records the temperature changes, dust levels
and water vapor in Mars' atmosphere. Mars researchers can also use each rover's
panoramic camera, which sits next to Mini-TES on the mast, to record dust devils,
clouds and wind - which has apparently brushed
the robot's solar arrays clean from time to time.
"[We're]
trying to continue these routine measurements and, more importantly, look for
patterns," Ghosh told SPACE.com.
In general,
Opportunity's landing site seems to run a bit warmer than Spirit's - about 4 to
6 degrees Celsius - while the surface temperatures at both sites hit their peak
at noon local time, he said, citing rover observations.
Building a
comprehensive understanding of Martian weather will be critical for future red
planet expeditions, since wind, dust storms and other atmospheric phenomena can
factor into a mission's landing, Ghosh added.
A large dust
storm that cropped up at Meridiani Planum in 2003 flung dust all the over
to Spirit's Gusev Crater landing site and reduced the density of the air there,
forcing mission planners to alter the rover's timeline for opening its parachute
during descent.
Meanwhile,
the weather
on Mars should begin to turn as the landing sites for Spirit and Opportunity
head further into fall.
In about
104 Martian days, or sol 775, rover handlers hope to have both rovers on
Sun-facing inclines to maximize the amount of sunlight striking their solar
arrays, Laubach said. The technique helped the rover mission weather the last
Martian winter.
Spirit is
currently rolling down Haskin Ridge as it descends
from the summit of Husband Hill and makes its way toward a feature dubbed 'Home
Plate.' Opportunity, meanwhile, continues to creep around Erebus
Crater.
A far-off
record
Despite
their accomplishments, Spirit and Opportunity have a long way to go to set an
endurance record on Mars. Both mission times pale in comparison with
NASA's twin Viking
missions.
Viking 1
and Viking 2, both of which set down on Mars in the summer of 1976, spent several
years recording Mars from their stationary landing spots. Viking 2's mission
ended in April of 1980 about 1,281 Martian days after landing when its
batteries failed. Viking 1, however, continued to function until Nov. 13, 1982,
more than four Earth years after arriving on Mars.
While their
longevity is impressive, the Viking missions had a powerful - literally -
advantage over Spirit and Opportunity. Both landers relied on radioisotope thermal
generators (RTGs) that converted heat from decaying plutonium into electricity
instead of solar arrays.
Dust
buildup has gradually degraded the amount of power available from the solar
arrays aboard Spirit and Opportunity. Both rovers were initially able to
generate about 900 watt hours of power from the available sunlight, though dust
has clouded their solar panels.
Spirit's
solar arrays currently produce about 650 watt hours while Opportunity's
generate up to 700 watt hours, Laubach said. A minimum of 300 watt hours is
required for Spirit to function, though Opportunity can operate on slightly
less, she added.
If Spirit
and Opportunity continue to perform as they have for the last few weeks, it's
entirely possible that they could make it through January 2006 and their second
Earth anniversary exploring the red planet, mission managers said.
"Though
certainly they could die tomorrow, that's just a fact," Laubach said, adding
that she and other rover team members have been amazed at the mission's science
output so far and hope for continued success. "We certainly haven't seen
everything there is on Mars."
advertisement
