Mars' globe-engulfing
dust storm has died down during the past several weeks, but the two robotic
rovers on its surface now face the fallout of dust from the thin atmosphere.
Conditions
were so bad in early August that just before the launch of the Mars-bound Phoenix spacecraft, rover scientist Mark Lemmon feared
the demise of the Opportunity rover.
"There
was one sol [Martian day] when there was real uncertainty we'd hear from
Opportunity," said Lemmon, a planetary scientist at Texas A&M University. He added that the plucky robotic explorer almost entered a power-saving
mode that would have been dangerous "uncharted territory" for the
rover team.
Still,
Lemmon thinks the Mars rovers will persevere through the dusty
conditions.
"Mars
could throw worse storms at us, but for this season I think we have seen the
worst," he told SPACE.com in an e-mail. "We got a good
demonstration that Mars could kill them."
Red
blanket
Thin layers
of reddish powder have been accumulating on Spirit and Opportunity's solar
panels due to fallout, blocking light at levels comparable to conditions during
the worst periods of the storm, Lemmon said.
Scientists
use the measure "tau" to describe the light
blockage, where zero is perfectly clear and light blockage diminishes as
the figure increases. Tau grew to greater than 5 during the peak of the dust
storm.
"Unless
tau goes to 5 for several sols in a row, it looks like she's out of the
woods," Lemmon said of the Opportunity rover, which has born the brunt of
the dusty assault. Tau is currently around 3.3, he added.
Stifled
light can threaten the Mars rovers because their electronics need to stay above
-40 degrees Fahrenheit (-40 degrees Celsius)—below that and metal circuits can
shrink, snap and claim the rovers' lives.
On the
martian surface, temperatures are a bone-chilling average of about -81 degrees
Fahrenheit (-63 degrees Celsius).
To combat
the cold, the rovers rely on small internal radioactive heaters to stay warm
and regularly go into "sleep" mode to conserve energy. Lemmon
reported that both robots now gather above 240 watt-hours per sol, enough to
power a 120-watt light bulb for two hours. He said at least 160 watt-hours per sol
is required to keep the electronics alive and well.
"Spirit's panels are still cleaner than before the
storm, Opportunity's panels are dustier," Lemmon said. He added that
mission managers are thinking of ways to minimize accumulating dust, such as
tilting the solar panels, but most options seem more risky than simply toughing
it out.
"Once the dust settles, we can pray for wind," he
said. "Not too much, just enough to clean the panels."
Intrepid
explorers
Lemmon said
the rovers' journey has been an
amazing one, especially because they were expected to survive for only three
months after landing. They have explored the surface of Mars now for nearly three
years and seven months.
"I
know we're all as stunned as anyone when we look back on how much the rovers
have been able to do for us," Lemmon said.
As of sol
1,282, or August 13, 2007, Spirit surpassed the nuclear-power Viking Lander 2's
record and is now the second-oldest operational robot on Mars.
"A
solar-powered vehicle is now in second place ahead of one of the nukes, despite
these dust storms," Lemmon noted, referring to the nuclear-powered Viking
landers. Spirit and Opportunity technically are solar-powered, although they do
have the radioactive heaters.
While it
may take another grueling 959 sols (which will occur in April 2010 on Earth)
for Spirit to surpass the first Viking lander's operational record, Lemmon said
the rover team isn't planning on closing shop anytime soon.
"[Programmers]
apparently developed a 2010 patch for a small rover flight software
glitch," Lemmon said. "Just in case."
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