Early Mars Too Acidic, Salty for Life, Experts Say
Anne Minard in Boston, Massachusetts
for National Geographic News
|February 17, 2008|
Mars likely had liquid water early in its past—but it was probably too acidic and oxidizing for life, scientists say.
That's the latest news from the longer-than-expected visits to the red planet by NASA's rovers Spirit and Opportunity, said Andrew Knoll, a Harvard University researcher and member of NASA's Mars program.
"That's not a very good place to live, and it's a worse place for the kind of chemistry that we think gave rise to life on Earth," he said.
Knoll and other Mars scientists presented their latest results in Boston Friday at the annual meeting of the American Association for the Advancement of Science.
Related findings will be published in an upcoming issue of the Journal of Geophysical Research—Planets.
Spirit and Opportunity have been traversing the Martian surface for nearly 1,400 Martian days—well beyond their expected life spans of 90 days apiece.
The machines' most celebrated findings have come in geology, including evidence of water in the planet's past. But they've also shown that the water was high acidic and briny with dissolved minerals.
"At first, we focused on acidity, because the environment would have been very acidic. Now, we also appreciate the high salinity," Knoll said. "This tightens the noose on the possibility of life."
Even if life formed in such an unlikely scenario—there are salt-tolerant microbes on Earth, after all—they probably got a killing blow from meteorites.
About 3.9 million years ago Mars was pummeled by a heavy bombardment similar to the one that has pockmarked Earth's moon.
"We know that large meteorites can have a devastating effect on life," Knoll said. "There would have been a very high probability that the planet would have been hit by sterilizing meteorites."
The new findings come just as NASA's next envoy is nearing the Martian surface. The Phoenix mission, with a control room in Tucson, Arizona, launched in August and is slated to land on Mars in late May.
Steven Squyres, principal investigator for the Mars rovers, said that the mission shows how scientists have changed the way they study Mars's potential for life since the mid-1970s, when the Viking missions became the first craft to land on the planet's surface.
Viking searched for microbes in the soil where it landed, an approach Squyres called "overly simplistic and overly optimistic."
(Related: "Viking Mission May Have Missed Mars Life, Study Finds" [October 23, 2006].)
Phoenix, in contrast, is designed to dig beneath the surface and bring up buried ice. (See a photo gallery of the new lander.)
In the meantime, Knoll said, the search for life on Mars will continue—but scientists will have to change their approach.
A careful analysis is needed to see what sort of life could have developed in the unfriendly environs and how it would have survived, he pointed out.
It might also look different than we expect, he added.
"Taking a mouse trap and putting some cheese on it is not the best experiment we can do right now."
(Related: "Alien Life May Be 'Weirder"' Than Scientists Think, Report Says [July 6, 2007].)
The next rover mission, the Mars Science Laboratory, will incorporate many of these lessons, said project manager Richard Cook of NASA's Jet Propulsion Laboratory.
Most importantly, it will be able to analyze chemistry onboard, he pointed out.
Scientists involved with that mission—set to launch in the fall of 2009—are working to choose from among six candidate landing sites.
The researchers hope to send the new rover to a place where the terrain is ancient and has preserved conditions from an earlier era.
"If I were forced to vote, probably the best place to look for evidence of Martian life is in Mars' earliest history—the first five or six hundred million years," Knoll said.
It's possible that an earlier age on Mars was wetter and not as acidic or oxidizing.
"The best hopes for a story of life on Mars are at environments we haven't studied yet."
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