Scientists study Mars’ ‘most habitable zone’

By Leonard David

updated 3:48 p.m. ET March 30, 2009

WOODLANDS, Texas - Evidence is building that NASA's Phoenix Mars Lander plopped down on a microbe-friendly location.

The Phoenix probe, which descended to the Red Planet's surface last May, was designed to study the history of water and habitability potential in the Martian arctic's ice-rich soil. It did not pack instruments designed to find life. To date, there is no firm evidence that Mars ever hosted biology.

But researchers say the landing site has or had the ingredients necessary to support life as we know it.

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

Now four papers are under review for scientific publication, detailing four major discoveries from the mission, said Peter Smith, the Phoenix mission's principal investigator at the University of Arizona in Tucson.

Smith and other Phoenix scientists provided a review of what the spacecraft uncovered on the Red Planet at last week's 40th Lunar and Planetary Science Conference held here.

Microbial metabolism
Carol Stoker, a researcher at NASA's Ames Research Center — and a Phoenix science team co-investigator — noted that one goal of the Phoenix sampling at its Northern Plains landing site was to determine whether this environment may have been habitable for life at some time in its history.

Stoker said that, given our current understanding of life, the potential for habitability in a specific time and space takes in three factors:

• The presence of liquid water.
• The presence of a biologically available energy source.
• The presence of the chemical building blocks of life in a biologically available form.

In addition to these factors, temperature and water activity must be high enough to support growth.

A major Phoenix find in its digging into and gulping quantities of Martian soil was identifying perchlorate salt at its landing locale. Perchlorate and chlorate are compounds used for microbial metabolism — energy sources relied on by numerous species of microbes here on Earth, Stoker said.

At last week's meeting, Stoker rolled out a "habitability index" — an approach akin to the Drake equation to evaluate the probability of life in the universe.

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

Delving into the Phoenix data, while admittedly still a work in progress, Stoker said it provides key information about the potential habitability of a Red Planet environment ... and the data suggest that habitable conditions have occurred in modern times. That belief, she said, cries out for rovers and the ability to drill down into Mars.

"What you see is that Phoenix comes down as a clear winner — a much, much higher habitability index than any of the other sites," Stoker told conference attendees. "The Phoenix landing site is the most habitable zone of any location we have ever visited on Mars."

Crucial factors
Phoenix results have shown that no chemicals detrimental to all microbe life were found at its landing spot, said Tufts University researcher Suzanne Young, one of the scientists on a team working with the output from Phoenix's wet-chemistry laboratory. The lab is part of the suite of tools called the Microscopy, Electrochemistry and Conductivity Analyzer, or MECA for short.

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Several, but not all, of the crucial factors for bio-habitability were found by the Mars lander's wet-chemistry laboratory. Some factors could not be measured by the Phoenix, Young explained. The data from the full Phoenix mission point to no true negative, she said, so further missions would be necessary to complete the picture of habitability, and possibly life, on Mars.

"We have lots of microbes out there that can do things ... eat rock and release from it stuff that they need" — a process, Young added, that creates a viable energy system for other microbes.

The environment at the Phoenix site was pretty gentle, Young said. "We didn't find anything excessively toxic that's going to do bad things."

In terms of a habitability checklist, "we've got bunches of checkmarks in really good places," Young explained. "I think Phoenix really did expand the possibility for serious consideration of looking for past and maybe even present life on Mars ... but it's still a work in progress," she said.

Need to go back
For now, the Phoenix Mars Lander mission is over.

As the craft's available solar power declined with the approaching Martian winter, the mission was declared finished — maybe, anyway — on Nov. 2 when controllers on Earth were unable to re-contact the robot.

"We will try 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," he added.

Young agreed that a repeat landing by a spacecraft near the northern polar region is warranted.

"There are things 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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