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Lander Data Sheds Light on Mars Polar Water

Data fromthe now-defunct NASA Phoenix Mars Lander is shedding light on the current watercycle on Mars, particularly how water moves between the surface and theatmosphere in the northern polar region.

Phoenix's Thermal and Electrical ConductivityProbe (TECP), a forklike instrument that can be stuck in the air or the dirt,measured how water moves in and out of the surface as well as humidity in theatmosphere.

Data fromthe instrument shows that "the water in the atmosphere goes away everynight, and at the same time, particularly later in the mission" the amountof water stuck in soil would go up at night and come back down during the day,said TECP lead scientist Aaron Zent of NASA's Ames Research Center in MoffettField, Calif.

"Theseare water molecules that are interacting very strongly with the surface of themineral grains," Zent said today at a meeting of the American GeophysicalUnion in San Francisco.

Changes inhumidity and temperature (which can shift both with the Martian seasons andwith the wobble of Mars' tilt over the course of thousands of years) alter howmuch water is stored in the dirt, or what scientists call regolith.

If morewater is added to the atmosphere, "proportionately more of those [watermolecules] end up stuck as films of water" on the grains, Zent said.

The filmsof water stuck between the surface and the atmosphere could be an ideal habitatfor potential Martian microbes. Though there is no solid evidence for life pastor present on Mars, it's such clues of habitability that the probe was sent tolook for.

"Thereare microbes that live quite happily in that" on Earth, Zent said.

Clumpysoil

Phoenix, in part a replacement for thefailed Mars Polar Lander, landedin the Vastitas Borealis plains of Mars on May 25. That arctic site provided afresh perspective on the red planet.

In thefive-plus months it spent alive at its landing site, the spacecraft dugup samples of Martian dirt and confirmedthe presence of subsurface water ice. It analyzed surface samples for signsof the planet's past potential habitability.

While thebulk of the regolith that rovers and landers have encountered so far on Mars isloose, windblown dust and sand, the dirt at Phoenix's landing site was "incrediblyblocky, or clotty soil," said lead scientists for Phoenix's robotic arm,Ray Arvidson of Washington University in St. Louis.

This clumpinessimplies that "this material has been processed," Arvidson said, andthe processing agent appears to be water.

Dwindlingsunlight (caused by the transition from summer to fall at Phoenix's location,which is roughly equivalent to northern Alaska on Earth) and light-obscuringdust in the atmosphere finally pushed Phoenix below its power threshold on Nov.2. The final cost of the mission was estimated at about $475 million, accordingto NASA officials.

Phoenix's observations also show that theregion it landed in is a comparatively young environment on Mars.

"We'relooking at current Mars whereas other missions that have landed on Mars arelooking at ancient Mars," Phoenix principal investigator Peter Smith, ofthe University of Arizona in Tucson, said at today's briefing.

The nearbyHeimdall crater was dated to about 500 million years ago ? ancient by Earthstandards, but fairly recent terrain for Mars.

Mysteriesremain

Phoenix's wet chemistry lab showed thatthere "are tiny amounts of salts and larger amounts of perchlorate"in the surface layer around Phoenix, further building the case for the region'spast potential habitability.

"Ifthis were an Earth environment you would say that there are nutrients andenergy sources available" for microbes to use, Smith said.

Phoenix's Thermal and Evolved-Gas Analyzerfound that five percent of the landing site surface material is calciumcarbonate, a mineral formed in the presence of water. However, scientists don'tyet know whether the calcium carbonate formed at Phoenix's site or was blown infrom elsewhere.

The landeralso observed water vapor clouds, ground fogs and snowforming in the late Martian summer.

"It'sa very active weather environment," Smith said. Current Mars climatemodels likely would not have predicted such a dynamic atmosphere, "sowe're at a time now where we're going to have to reset those models" toget a more accurate idea whether the region was ever a wet environment, he said.

Throughoutthe coming months, Smith and his team will be further analyzing the data andworking in their labs to try and recreate the signatures of minerals from Phoenix's instruments.

  • Video ? NASA's Phoenix: Rising to the Red Planet
  • Special Report: Phoenix Mars Lander
  • Images: Phoenix on Mars!

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