Even as its
mission winds down, NASA's Phoenix Mars Lander has spotted snow falling from
the Martian sky.
Phoenix's camera and meteorological
equipment have shown
clouds and fog forming during the night as the air gets colder.
"This
is now occurring every night," said Jim Whiteway of York University in Toronto and lead scientist for Phoenix's Meteorological Station.
A laser
instrument that is pointed directly up into Mars' atmosphere has also detected
snow from clouds about 2.5 miles (4 kilometers) above the spacecraft's landing
site. Data show the snow vaporizing before reaching the ground. There are no
conventional photographs of the snowfall. Scientists knew from previous studies
that it snows
on Mars. But they've never seen it happening from the ground.
"Nothing
like this view has ever been seen on Mars," Whiteway said. "We'll be
looking for signs that the snow may even reach the ground."
The craft
has also seen new hints of the planet's watery past. Meanwhile, mission
scientists are trying to squeeze in all the science they can before the Martian
sun sets for the winter, including a surprise attempt to switch on Phoenix's as-yet unused microphone.
Mission
scientists announced the plans for Phoenix's
remaining weeks of activity at a press conference Monday.
They also
revealed information that will help them to "begin rewriting the book of
Martian chemistry," said Michael Hecht, of NASA's Jet Propulsion
Laboratory (JPL) in Pasadena, Calif., and lead scientist for Phoenix's
Microscopy, Electrochemistry and Conductivity Analyzer (MECA).
Phoenix landed in the northern plains of
Mars on May 25 and has been using its onboard instruments to analyze the
Martian dirt and subsurface ice layer at its landing site above Mars' arctic
circle. The mission, extended once by NASA through the end of September, was
extended again earlier this month through the end of December.
But it's unlikely
Phoenix will last that long.
What's
next
As winter
approaches in the Northern hemisphere of Mars, the sun dips lower in the
horizon, providing Phoenix' solar arrays with less and less sunlight to convert
into electricity to run its instruments. Eventually the sun will set above the
arctic circle alltogether.
As this
happens, the Phoenix team is "trying to get the most out of these science
instruments in the last few days," said Barry Goldstein, Phoenix project
manager, also of JPL.
Scientists
working on Phoenix's Thermal and Evolved-Gas Analyzer are planning to attempt
to fill the instrument's four (of eight total) remaining
ovens will Martian dirt and ice samples. The team particularly wants to get
a pure-ice or ice-rich sample, said TEGA lead scientist William Boynton of the University of Arizona, Tucson.
The team
has run into problems gathering ice samples, with the "ice almost welding
itself to the inside of the scoop" on the end of Phoenix's robotic arm,
Boynton said, though he added: "We're still optimistic that we can fill
all four before we run out of power."
Phoenix will also look for signs of
organics in the samples delivered to TEGA, by comparing them to a blank brought
to rule out any contamination brought from Earth. While they would be a
thrilling find, organics would not necessarily indicate life — they could be
deposited by comets and preserved in the ice, said Phoenix principal
investigator Peter Smith, also of the University of Arizona.
The lander
will also look at the different isotopes (or types of an element with different
numbers of neutrons) in the subsurface ice and the water vapor in the Martian
air to see whether the two water sources interact, Smith said.
As a bonus,
mission scientists are going to try to switch on the microphone that was
originally installed on Phoenix to be used during the lander's descent. While
that use was scrapped, the Phoenix scientists have to decided now to "try
and listen to Mars for the first time," Smith said.
"We're
not sure if it's going to work, but we're going to make a try," he added.
Phoenix
will also try to sample the dirt underneath
a rock, dubbed "Headless," that it successfully moved with its
7.7 foot-long (2.4 meter-long) robotic arm last week. Images have already shown
some color differences in the dirt under the rock.
"We're
hoping to find a different chemistry under the rock than next to the
rock," Smith said.
New
Martian chemistry
So far, the
chemistry of the surface layers near Phoenix's landing site has been a bit
different that anticipated.
TEGA has
identified several minerals that suggest that the surface there has interacted
with water sometime in the Martian past. These include silicates similar in
structure to mica, only softer, and calcium carbonate. Examples of carbonates
on Earth are chalk and antacid tablets.
The suite
of MECA instruments have shown that the pH of the soil near Phoenix is
approximate 8.3 — or slightly basic — "almost exactly the pH of ocean
water on Earth," Hecht said.
MECA has
also found evidence of perchlorates, which could act as an energy source for
any potential past Martian microbes and could have a significant impact on
Mars' water chemistry.
For one
thing, they could help explain why Phoenix's fork-like
probe has found that "the soil in our little corner of Mars is very,
very dry," Hecht said. Perchlorate could be soaking up any water in the
soil above the ice layer, he explained.
Based on
models of Phoenix's energy decline, mission engineers don't expect Phoenix to last much past late November. Eventually, the sun will set on Phoenix
completely, and carbon dioxide ice will likely deposit on it. That combined
with the ever-decreasing temperatures of winter will likely destroy the
spacecrafts components.
"Nobody
anticipates that the vehicle will survive that harsh winter," Goldstein
said.
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