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Thursday, August 7, 2008

NASA shoots down Mars rumors: we're not sure what we've got

Over the weekend, rumors started rebounding around the Internet: initial work from the Mars Phoenix lander had found something that was evidence relevant to the possibility of life on Mars, and the President had been briefed. Before the jokes regarding the President and intelligent life had subsided, other rumors suggested that NASA had found a toxin that was incompatible with life. NASA decided to end the speculation, and dragged members of the Phoenix team into an early-afternoon press conference. Phoenix may have found an abundance of a specific chemical on Mars, but the researchers involved aren't even sure what it is yet.

NASA spokesman Duane Brown introduced the press conference by referencing what he called the "speculation and rumors," and described it as an attempt to set the record straight. The scientists, he said, were doing so reluctantly, as they are being forced to present the results before their instruments were even producing an unambiguous result, much less one that had passed peer review. Mike Meyer, the head of NASA's Mars efforts, said, "we're here today to announce a nonannouncement—more experiments and time are needed to resolve the results of the science experiments."

The project lead, Peter Smith, seemed a bit more accepting. Describing it as a "break with scientific tradition," he nevertheless said that it was a great opportunity that he likened to "opening a window to allow the public to see the scientific process in action." Although that process is still dealing with multiple, potentially contradictory, indications, the strongest one they have is that there are significant amounts of perchlorate on Mars.

Perchlorate's chemical formula is ClO4-, and is found naturally on earth, typically as part of a salt with a positive ion. It was once thought to be such a strong oxidizing agent that it was considered incompatible with organic compounds, leading to some of the rumors that circulated about findings of a chemical that could kill. Since then, however, it has not only been found in deposits with organic compounds, but microbes have been discovered that actually use it as the primary oxidizing agent in their metabolism.

The problem is that two instruments on the lander are providing somewhat contradictory results. Michael Hecht spoke about the MECA instrument, which runs wet chemistry experiments. The instrument contains a number of sensors that are tuned to pick up the presence of different classes of ions released as the sample heats up. The instrument that picks up perchlorate and (to a lesser extent, nitrates) registered a huge spike—so large, the scientists didn't trust it. Since then, however, a second sample and a test with an earth-bound version of MECA produced the same spike, so the MECA folks are feeling confident.

The Rosy Red sample on its way to MECA
NASA/JPL-Caltech/University of Arizona/Max Planck Institute

The people behind the TEGA instrument, represented by William Boynton, are less sure. TEGA probes the composition of gases released when samples are heated using a mass spectrometer, and it has seen large amounts of oxygen (consistent with perchlorate), but no chlorine. Only a number of perchlorate salts will decompose in a way that releases chlorine, so that's not a complete shock, but the team is now trying to figure out ways to detect some of the others.

Assuming the finding's right, what's it all mean? It's really hard to say. Different perchlorate salts can have very different properties, so nailing down precisely what's present in the soil will be critical. Once that's done, data from elsewhere on the planet can be reevaluated to determine whether its presence might be widespread. Given that some organisms use it as part of their basic biochemistry, it's clearly not incompatible with life, but it doesn't seem to make life—past or present—any more likely on Mars.

The researchers note that, because of its strong oxidizing properties, perchlorate was actually used in the propulsion system of one stage of the Delta rocket that got Phoenix to Mars in the first place. But dry runs with the instruments showed that they weren't contaminated, and the shovel has spent a month scraping itself clean on various soil samples, so any contamination there should have declined significantly. Amusingly, the scientists have been giving each soil sample brought on board a nickname, so the press conference was peppered with references to "wicked witch," "baby bear," "rosy red," and "sorceress."

So, as mentioned right at the start, this was a bit of a nonannouncement. We've got a strong indication that perchlorate is probably present, but we're not even positive yet, much less precisely the form it's in. About the clearest thing that can be said about the results came from Michael Hecht, who said, "they can potentially keep a lot of graduate students busy for a very long time."

Original here

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