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The dirt's okay. The Phoenix lander has found perchlorate minerals in martian soil. That caused an Internet stir but doesn't bear on the potential for life.

NASA/JPL-Caltech/University of Arizona/Texas A&M University

NASA Quashes Rumors of Life on Mars

Many a scientist dreams of finding evidence of life on other planets. Today, those working with NASA's Phoenix lander, which touched down on the icy plains of polar Mars 10 weeks ago, had to perform a slightly less exciting task: They dropped everything to make a "nonannouncement," as one NASA official put it, and put to rest rumors that they had such signs.

There is no cover-up, Phoenix scientists declared. They weren't hiding evidence of life on Mars, as blogosphere buzz had it, or even signs that life could ever have survived on Mars. They were just trying to do their science as best they knew how before announcing a fascinating (at least to planetary geochemists) discovery that they've found a class of chemicals called perchlorates in the martian soil.

The fuss started with a relatively restrained news story posted last Friday on headlined "White House Briefed On Potential For Mars Life." Restrained, but that was much the way the huge hullabaloo over signs of life in a martian meteorite got started in 1996 (Science, 16 August 1996, p. 924). One news report over the weekend even claimed that a paper on the discovery had been submitted to Science, as had been the case a decade ago. Soon speculation was running rampant on the Web, which prompted "an unusual step and a break with scientific tradition," as Phoenix principal investigator Peter Smith of the University of Arizona, Tucson, put it on today's press teleconference. Phoenix scientists would publicly discuss a NASA finding about which they still had doubts.

The tentative discovery is perchlorate salts (a chemical containing a chlorine atom with four oxygens attached) in the soil near the Phoenix lander. The wet chemistry analyzer on Phoenix had detected perchlorate in two soil samples, while two "bake tests" had yielded the necessary oxygen but not the chlorine that some kinds of perchlorate would release. Given the lingering uncertainty, Phoenix scientists were waiting for more results from the lander and the lab on earth, Smith said, at least until word of a White House briefing leaked out. NASA spokesperson Dwayne Brown quashed that part of the story; no one outside of NASA had been briefed, he told the teleconference.

As to perchlorates and the potential for life on Mars, that part of the story didn't pan out as the buzz would have it. Although perchlorate is nasty enough that it's recommended not to exceed 25 parts per billion in U.S. drinking water, it's not a big deal for most terrestrial life, Phoenix scientists said. Some microbes actually use it as an energy source. On Mars, it may have been made in the atmosphere by solar ultraviolet light or in the ice and soil by cosmic rays. Either way, perchlorates don't seem to bear one way or the other on the potential for life on Mars, Phoenix scientists told the teleconference. They'll let the public know if they find otherwise.

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