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.
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.
NASA's Phoenix spacecraft has discovered two minerals on Mars that suggest water was there in the past.
Scientists reported Monday that the minerals — calcium carbonate and sheet silicate — don't usually form without the presence of liquid water.
Phoenix landed in the Martian arctic plains in May on a three-month mission to study whether the environment could be friendly to microbial life. One of its main goals is to probe whether the ice ever melted.
NASA recently extended the mission through the end of the year, depending on whether Phoenix can survive that long.
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