'Most Habitable Zone' on Mars Revealed

WOODLANDS,Texas — Evidence is building that NASA?s Phoenix Mars Lander plopped down on amicrobe-friendly location.

Descendingonto Mars on May 25, 2008, Phoenix was designed to study the history of water andhabitability potential in the Martianarctic?s ice-rich soil. It did not pack instruments designed to find life. Todate, there is no firm evidence that Mars ever hosted biology.

Butresearchers say the landing site has or had the ingredients necessary tosupport life as we know it.

Recently,scientists revealed controversial evidenceof liquid water at the landing site. Water is a key to life.

Now four papers areunder review for scientific publication on four major discoveries from themission, said Peter Smith, the Phoenix mission?s principal investigator at theUniversity of Arizona in Tucson.

Smith and other Phoenixscientists provided a review of what the spacecraft uncovered on the red planetat last week?s 40th Lunar and Planetary Science Conference held here.

Microbial metabolism

Carol Stoker of NASA?sAmes Research Center — and a Phoenix science team co-investigator — noted thatone goal of the Phoenix sampling at its Northern Plains landing site was todetermine whether this environment may have been habitable for life at sometime in its history.

Stoker said given ourcurrent understanding of life, the potential for habitability in a specifictime and space takes in three factors: the presence of liquid water; thepresence of a biologically available energy source; and the presence of thechemical building blocks of life in a biologically available form. In additionto these factors, temperature and water activity must be high enough to supportgrowth.

A major Phoenix find inits digging into and gulping quantities of Martian soil was identifying perchloratesalt at its landing locale. Perchlorate and chlorate are compounds used formicrobial metabolism — energy sources relied on by numerous species of microbeshere on Earth, Stoker said.

Stoker rolled out at themeeting a ?habitability index? — an approach akin to the Drake equation toevaluate the probability of life in the universe.

As a general conclusion,Stoker valued the Phoenix landing site as having a higher potential for lifedetection than any site previously visited on Mars. Moreover, the icy material thatwas sampled might periodically be capable of sustaining modern biological activity.

Delving into the Phoenixdata, while admittedly still a work in progress, Stoker said it provides keyinformation about the potential habitability of a red planet environment ?andthe data suggest that habitable conditions have occurred in modern times. Thatbelief, she said, cries out for rovers and the ability to drill down into Mars.

?What yousee is that Phoenix comes down as a clear winner — a much, much higherhabitability index than any of the other sites,? Stoker told conferenceattendees. ?The Phoenix landing site is the most habitable zone of any locationwe have ever visited on Mars.?

Crucialfactors

Phoenixresults have shown that no chemicals detrimental to all microbe life were foundat its landing spot, said Tufts University researcher Suzanne Young, one on a teamscientist working with the output from Phoenix'swet chemistry laboratory —?part of the suite of tools called theMicroscopy, Electrochemistry and Conductivity Analyzer, or MECA for short.

Several,but not all, of the crucial factors for bio-habitability were found by the Marslander?s wet chemistry laboratory. Some factors could not be measured by thePhoenix, Young explained. The data of the full Phoenix mission points to notrue negative, she said, so further missions would be necessary to complete thepicture of habitability, and possibly life, on Mars.

?We havelots of microbes out there that can do things?eat rock and release from it stuffthat they need? — a process, Young added, that creates a viable energy systemfor other microbes.

The environmentat the Phoenix site was pretty gentle, Young said. ?We didn?t find anythingexcessively toxic that?s going to do bad things.?

In terms ofa habitability checklist, ?we?ve got bunches of checkmarks in really goodplaces,? Young explained. ?I think Phoenix really did expand the possibilityfor serious consideration of looking for past and maybe even present life on mars?but it?s still a work in progress,? she said.

Need togo back

For now,the MarsLander mission is over.

As thecraft?s available solar power declined with the approaching Martian winter, themission was declared finished — maybe, anyway — Nov. 2 when Earth controllerswere unable to re-contact the robot.

?We willtry to get it back in October but the chances are poor,? Smith said. ?However,it is known as the Phoenix mission and we do have a chance. We may be back,? headded.

Youngagreed that a repeat landing by a spacecraft near the northern polar region iswarranted.

?There arethings we couldn?t do. There are things we didn?t do," she said."There are things that serendipity could have delivered to us and didn?t.But we have not found any impossibilities?we?ve not found anything that?s a no.And we have added a lot to the possibility — and so more missions are needed.We need to go deeper?we need to go back."

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LeonardDavid has been reporting on the space industry for more than four decades. Heis past editor-in-chief of the National Space Society's Ad Astra and SpaceWorld magazines and has written for SPACE.com since 1999.