Thriving below. The lander isn't capable of actually detecting life, and in any case, cosmic rays have undoubtedly sterilized Mars's surface, says Carol Stoker, who works on the Phoenix project at the NASA Ames Research Center. But future missions may drill into the dirt. "Microbes could be getting along nicely under the surface," she says.
Recent discoveries on Earth bolster the possibility that life might thrive under the Martian soil and in other seemingly inhospitable locales. Scientists are stocking an ever-expanding zoo of "extremophiles"—single-celled organisms that survive the harshest of conditions. These microbes live in boiling heat or icy cold, in nail-dissolving acid pools or even deep underground, divorced from all sunlight. The subterranean ones, discovered in 2006 by a NASA-funded team in a South African gold mine, survive on energy derived from natural radioactivity in rock. This May, scientists from Cardiff University in Wales added to the extremophile menagerie when they found microbes teeming in sediments collected more than a mile beneath the North Atlantic seafloor. The extremophile discoveries "really expand our understanding of what is a habitable environment," says Carl Pilcher, director of the NASA Astrobiology Institute, which funds such work.
In addition to looking for microbes on Mars, NASA plans future missions that "follow the water" to other promising outposts in our solar system, namely Europa and Titan. The former, a moon of Jupiter, harbors a vast liquid-water ocean under a miles-thick carapace of ice. Titan, a satellite of Saturn shrouded in a dense atmosphere, may also harbor liquid water under its surface. "The potential for something interesting going on under the surface of Titan is probably as high as it is on Mars," says Rummel.
But, like Phoenix, all of NASA's near-future missions share a common shortcoming: They can find environments conducive to life but not detect life itself. "We're trying for a series of base hits rather than going for a big, risky home run," says Rummel.
That makes SETI the only project with grand-slam potential. Astronomer Shostak boldly predicts that SETI will hear from a real E.T. within 20 years. "A lot of my colleagues don't like that prediction. They think it's going too far," Shostak says. But he's convinced that "we're going to find out, one way or another, that biology is not a miracle."