The end
seems to have finally come for NASA's Phoenix Mars Lander mission at the
planet's north pole, scientists said Monday.
"At
this time we're pretty convinced that the vehicle is no longer available for us
to use," said Phoenix project manager Barry Goldstein of NASA's Jet
Propulsion Laboratory in Pasadena, Calif.
"We
knew this would happen eventually," Goldstein added.
Mission controllers lost touch with the
lander on Nov. 2. That "was actually the last time we actually heard
form Phoenix," Goldstein said. The spacecraft has been studying the arctic
surface of the red planet for just over five months, since landing there May
25.
During the
course of its
mission, Phoenix scooped up samples of the Martian dirt and subsurface
water ice at its arctic landing site and analyzed them for signs of the
planet's past potential habitability. Phoenix touched down on the northern
plains of a region known as Vastitas Borealis. The area is at a latitude on
Mars equivalent to northern Alaska on Earth.
Phoenix successfully completed its mission
objectives at the end of its three-month primary mission in August. The
mission's cost was ultimately about $475 million (up from the $420 million for
its original three-month mission).
"NASA's
gotten what they wanted out of this mission," said Doug McCuistion,
director of the Mars Exploration Program at NASA Headquarters in Washington, D.C., though Phoenix's "demise is a little earlier than we'd hoped."
Phoenix's big finding was to confirm the presence
of water ice under the surface dirt layer in the northern plains. Phoenix "fulfilled dreams of touching Martian water for the first time,"
McCuistion said.
It also
found that the dirt at the lander's location was more alkaline than the soil
sampled by the Mars Exploration Rover missions (Spirit and Opportunity) closer
to the equator. Phoenix's measurements also unexpectedly turned up signs of
perchlorate, a possible source of energy for any potential life that could have
once graced the Martian surface.
Phoenix's
science team will now begin to thoroughly analyze all the data received from
the lander, said Phoenix Principal Investigator Peter Smith of the University
of Arizona in Tucson, Ariz.
"Phoenix has given us some surprises, and I'm confident we will be pulling more gems from
this trove of data for years to come," Smith said.
The mission
was "definitely the thrill of my life," he said.
The
lander's power supplies have been steadily diminishing in recent weeks as the sun
dips toward the horizon with the approach of fall and winter to Mars' northern
hemisphere. Phoenix went into its inactive
safe mode briefly on Oct. 28, when a dust storm obscured the sky and
limited the amount of sunlight hitting the lander's solar arrays. Phoenix restarted once the sun came up the following day.
For the
next few days, Phoenix would lose power or "brown out" at night, then
wake up again when sunlight hit its solar arrays the following morning. Mission engineers tried to turn off any unnecessary instruments and heaters to keep the
batteries alive, but "we were unsuccessful in keeping the batteries from
browning out," Goldstein said.
The team
was planning to send new instructions to the lander, but "unfortunately
that high condition of dust lasted for some days there" and kept Phoenix from operating, Goldstein said.
The
sequence of events that led to Phoenix shutting down were "exactly
play-by-play what we anticipated doing," Goldstein said, though they came
about three weeks earlier than anticipated. Mission engineers had originally
hoped the lander would last through the end of November, acting as a weather
station and using its camera to photograph the change of season.
Phoenix
has effectively ended all science operations, though the team will keep
listening for any signals from the spacecraft relayed through NASA's Mars
orbiters until solar conjunction (when the sun comes between the Earth and
Mars) begins in a few weeks.
The sun is
continuing to go down about 5 minutes earlier every day at Phoenix's location.
Come April 1, it will set completely beneath the horizon for three months. The
sun won't be high enough in the sky to generate enough energy to re-power
Phoenix until at least mid-October 2009, Goldstein said, though he think it's
unlikely the spacecraft will re-awaken because of the extreme
cold and carbon dioxide ice it will be subjected to.
Though no
one on the team expects that Phoenix will once again live up to its name and
rise again, there's always the "hope that the vehicle will surprise us
again," Goldstein said.
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