Updated
2:05 p.m. ET.
A raging
dust storm on Mars has cut power to NASA's twin rovers to dangerously low
levels, threatening an end to the mission.
The rovers
were slated to operate for only 3 months but have been on Mars more than 3
years, so mission officials have had ample time to ponder their
eventual silencing.
The storm
presents perhaps the rover team's biggest challenge, NASA said in a statement
today. Scientists said the storm, which has been brewing for nearly a month, is
blocking around 85 to 90 percent of all sunlight to the surface.
The rovers,
Opportunity and Spirit, rely on sunlight to charge their solar panels, and one
or both rovers could be damaged permanently or even
disabled by the limited solar power, officials said.
SPACE.com reported the storm's fresh
severity earlier today.
The
forecast
Scientists
fear the storms might continue for several days or weeks. If the sunlight is
further slashed for an extended period, the rovers will not be able to generate
enough power to keep warm and operate at all, even in a near-dormant state, the
statement said.
The rovers use electric heaters to keep
vital core electronics from becoming too cold.
"We're
rooting for our rovers to survive these storms, but they were never designed
for conditions this intense," said Alan Stern, associate administrator of
NASA's Science Mission Directorate.
Steve
Squyres of Cornell University, who is the lead scientist of the Mars
Exploration Rover Project, said the direct sunlight to the rovers is at an
all-time low.
"To
give you a sense of the 'thickness'
of the dust, the brightness of the sun as viewed from the surface is now
down to less than 1 percent of what it would be with a perfectly transparent
atmosphere," Squyres said. "Of course, Mars never has a perfectly
transparent atmosphere, but the sun is still very faint."
The rovers'
scientific operations were stopped Wednesday.
"This
is, I think, one of the most significant challenges we've faced over this
entire mission," Squyres told SPACE.com today. "The nature of
the risk is well understood, but the magnitude of the risk is not. We simply
don't know what's going to happen next."
Martian weather
is unpredictable, in part because there are few monitoring instruments and
no formal weather forecasting agency as on Earth.
"Whatever
we do, though, the problem is not going to get much better rapidly,"
Squyres said. "I think that we have a good chance. If Mars really wants to
kill these vehicles it can, but we have a lot of things working in our
favor."
The cold
facts
If the
rovers expend too much energy, they may be unable to warm their electronics and
prevent circuit-snapping temperatures.
Before the
dust storms began blocking sunlight last month, Opportunity's solar panels had
been producing about 700 watt hours of electricity per day, enough to light a
100-watt bulb for seven hours. When dust reduced the panels' daily output to
less than 400 watt hours, the rover team suspended driving and most
observations, including use of the robotic arm, cameras and other site-inspection
instruments.
On Tuesday,
July 17, the output from Opportunity's solar panels dropped to 148 watt hours,
the lowest point for either rover. On Wednesday, the output dropped even lower,
to 128 watt hours.
Mark
Lemmon, a planetary scientist at Texas A&M University and member of the
rover team, said Opportunity is consuming 130 watt hours per martian day in its
"sleep mode." If the negative balance continues without a break,
Lemmon explained, the rover may malfunction in a matter of weeks.
"Even
with a 10-20 watt hour gap, we'd have a healthy rover for over a week,"
Lemmon said in a telephone interview. "We've never been in situation where
we've been in any imminent danger of a battery depleting, but it's
possible."
NASA
engineers are working to protect the rovers, especially Opportunity, which is
experiencing the brunt of the
dust storm. The rovers are showing robust survival characteristics. Spirit,
in a location where the storm is currently less severe, has been instructed to
conserve battery power by limiting its activities.
"We
are taking more aggressive action with both rovers than we needed before,"
said John Callas, project manager for the twin rovers at NASA's Jet Propulsion
Laboratory.
Hanging
on
By Opportunity's 1,236th Martian day, which ended Tuesday, driving and all science
observations had already been suspended. The rover still used more energy than
its solar panels could generate on that day, drawing down its battery.
"The
only thing left to cut were some of the communication sessions," Callas
said.
To minimize
further the amount of energy Opportunity is using, mission controllers sent
commands on Wednesday, July 18, instructing the rover to refrain from
communicating with Earth on Thursday and Friday. This is the first time either
of the rovers has been told to skip communications for a day or more in order
to conserve energy.
Since the
onset of the storms, engineers have said a similar storm could be
weathered by NASA's next Mars mission, a robotic lander. Human missions to
Mars, a plan for the distant future, would be challenged
greatly by storms like this, officials say.
Even if
either of the rovers do malfunction, Lemmon explained all would not be lost.
"This
is a really good scientific opportunity to understand how dust storms on Mars
work, how they dissipate and how the dust moves around inside them," he
said. "I think we'll be able to use the information we're getting now to
look ahead to future mission to Mars."
SPACE.com's
Robert Roy Britt contributed to this story.
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