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Earth-invading aliens will haunt television screens this fall when the networks air knockoffs of the popular "X-Files" science fiction series. But scientists won't have to turn on the tube for their own drama featuring putative visitors from another world. Their show kicked off in a blaze of publicity on 7 August, with the early release of a paper from this issue of Science. It will be played out over the coming months in scientific meetings and journals as researchers debate the meaning of the findings, which appear on page 924. There, a diverse group of nine researchers from five institutions led by geologist David McKay of NASA's Johnson Space Center (JSC) in Houston argue that the best explanation for three different minerals, an organic residue, and bacteria-like structures found together in a meteorite that was blasted from the surface of Mars is ancient life on the Red Planet.
"We are not claiming that we have found life on Mars," cautions McKay. "And we're not claiming that we have found the smoking gun, the absolute proof, of past life on Mars. We're just saying we have found a lot of pointers in that direction." He adds that no one line of evidence requires their dramatic conclusion that minute bacteria flourished on Mars billions of years ago, when planetary scientists believe it was a wetter and more hospitable place. But when the evidence is taken together, "we consider that to be the most reasonable interpretation," he says. "We welcome other people looking at [the meteorite] and making other interpretations."
The few researchers familiar with the evidence before the paper was released (Science lifted the embargo on the paper when news of the findings leaked out) didn't need any prompting to suggest other interpretations. "I think it's very unlikely they have remnants of biological activity," says William Schopf of the University of California, Los Angeles, who has spent his career separating microfossils of early life on Earth from impostors. Nonetheless, "this is a first step; additional work needs to be done" to search the meteorite for more persuasive clues.
Others are just a bit more upbeat. "I'm not convinced," says interplanetary dust particle specialist Donald Brownlee of the University of Washington, "but I think they have made a...