As winter's icy grip prepares to
take hold of the northern plains of Mars, NASA scientists are scrambling to
fill all of the instruments aboard the Phoenix Mars Lander with samples of
Martian dirt before the sun sets below the horizon and the spacecraft loses its
energy source.
The next dirt sample delivered to the
lander will go into the fourth and final cell of Phoenix's wet chemistry
laboratory, according to the team's latest plans. The team also plans to fill
the last four of the eight one-time-use ovens of the lander's
Thermal and Evolved Gas Analyzer (TEGA), delivering dirt to each oven before
analysis is complete on the previous sample.
The strategy is to take as many
samples of the dirt as possible while there is still enough energy for the
spacecraft to use its robotic arm to dig up the Martian surface.
Phoenix gets its energy from its two solar
panels that stick out from it like wings. As the northern Martian summer comes
to a close, the sun is beginning to dip below the horizon, reducing the amount
of sunshine reaching the solar panels and therefore the amount of electricity they
generate to run the lander.
"Now that the sun is not
constantly above the horizon at our landing site we are generating less power
every sol," said Phoenix project manager
Barry Goldstein of NASA's Jet Propulsion Laboratory in Pasadena, Calif.
"When we landed in late May, and through much of our mission, we generated
about 3,500 watt-hours every sol [or Martian day]. We are currently at about
2,500 watt-hours, and sinking daily. With the remaining sols we need to scurry
to squeeze the last bit of science out of the mission."
(One hundred watt-hours is
equivalent to the power needed to illuminate a 100-watt bulb for one hour.)
The $420 million Phoenix
mission is digging up and analyzing samples of the Martian dirt and
rock-hard subsurface ice layer in the northern plains of the Martian arctic, in
an effort to shed light on Mars' past potential habitability. Phoenix is currently in the middle of a
one-month mission extension that began after the primary mission ended at the
beginning of September.
The sample that will be delivered to
the last of the lander's wet chemistry lab cells will
be from the "Snow
White" trench on the eastern end of Phoenix's work area. A sample from this
trench analyzed by TEGA in July confirmed the presence of water ice on Mars.
The wet chemistry lab, which dissolves the dirt sample in water brought from
Earth to look for soluble minerals, has also previously analyzed a Snow White
sample; it identified magnesium, sodium, potassium, chloride and perchlorate in the surface regolith.
The perchlorate finding was of particular interest because
of the compound's potential to be an energy source for microbes, but analyses
of the dirt in TEGA haven't turned up a signal of perchlorate.
Mission scientists planned to keep looking for
the signal in future TEGA samples.
The next TEGA sample will also come
from Snow White. The team plans to use the rasp on the end of Phoenix's robotic arm to churn up ice-rich
material from the hard floor of the trench.
TEGA's tiny ovens bake the surface samples
to different temperatures and analyses the vapors given off at each temperature
increase to identify the chemical make-up of the Martian surface dirt.
A valve that pushes the vapors given
off by the sample to the lander's mass spectrometer
for analysis is no longer reliable, NASA said, but researchers think that the
remaining samples going into TEGA will give off enough carbon dioxide and water
vapor to carry any other vapors along to the spectrometer.
The Phoenix team is also testing possible
workarounds for an unexpected opening of another valve in the instrument.
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