This story was updated at 5:56 p.m. ET.
Despite recent media reports that NASA found evidence for life on Mars, the U.S. space agency says proof that we are not alone is still a ways off.
A Wednesday article in the U.K.'s "The Sun" newspaper entitled, "NASA: Evidence of Life on Mars," reported that they agency had unveiled "compelling evidence" for Martian organisms. But NASA officials and veteran Mars mission scientists say "no."
"This headline is extremely misleading," said Dwayne Brown, a spokesman for NASA based at the agency's headquarters in Washington, D.C. "This makes it sound like we announced that we found life on Mars, and that is absolutely, positively false."
The piece claimed that the Mars Exploration Rovers Spirit and Opportunity, which have been wheeling around the surface of the red planet since January 2004, found pond scum, which the paper calls "the building blocks of life as we know it."
"I think they have taken this stuff out of context," Brown said.
Such a discovery would truly have been groundbreaking, since pond scum, scientifically known as cyanobacteria, are actually a form of life themselves, not just building blocks for it.
"I can only assume that the Sun reporter misunderstood," said Cornell University planetary scientist Steve Squyres, principal investigator of the Mars Exploration Rover project, who was quoted in the story. "What Spirit and Opportunity have found is sulfate minerals... not organic materials, not pond scum, and not the building blocks of life as we know it.
Water = life?
The article, which has been widely quoted across the Web, appeared after NASA scientists spoke to reporters from an astrobiology conference celebrating the 50th anniversary of research aimed toward searching for life beyond Earth.
The piece claims, "The recent missions have gathered evidence of sulphates on Mars, a strong indication there is water on the planet and therefore life."
But just because there might be water does not mean that life follows.
"Evidence of water does NOT mean that there was life," Squyres wrote in an e-mail. "We believe that water is necessary for life, but not that it is sufficient to assure life. The "...and therefore life" part of the statement therefore is simply wrong."
While scientists have not yet discovered proof of living things anywhere in the universe beyond Earth, they are getting closer to knowing where to look and how to recognize the signs of life if they are present.
And Brown said that NASA's various Mars missions, including the rovers and spacecraft such as the Mars Reconnaissance Orbiter and the 2001 Mars Odyssey ? both currently in orbit around the red planet ? are revealing a wealth of clues about the possibility of life there. It's just too soon to know for certain.
Past life controversies
Claims of finding life on Mars are not new.
In August 1996 NASA researchers presented a Martian rock that they said showed clear signs of being affected by life. The rock, which had landed in Antarctica, contained holes and markings that appeared to have been formed by bacterial colonies living on it.
The announcement made a huge splash, but in the decade that followed, most researchers have dismissed the claims of life, and found non-living explanations for the rock's markings.
There has likewise been controversy over pronouncements that Mars could not possibly harbor life. In 1976, NASA's Viking 1 and 2 landers touched down on the Martian surface and performed three separate experiments to search for signs of life. Despite having sensitivities to detect organic molecules of a few parts per billion, no organic compounds were ever detected by either lander. Many scientists declared that Mars therefore must not have microbial organisms on its surface.
Yet a more recent study found that perhaps the Viking experiments were not so sensitive after all, and cast doubt on the conclusion that microbes aren't there.
Besides Mars, some particularly promising spots in the solar system include the Saturnian moons Titan ? with its lakes of methane and ethane ? and Enceladus, with its plumes of water vapor, and Jupiter's moon Europa, which is thought to harbor an underground ocean.
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