"Planets are as common as bugs," Shostak said. "It would be weird in the extreme if all the planets out there are like Jupiter and none of them is able to support life. That seems incomprehensible."
Many of the celestial bodies that were thought to be inhospitable to life just a few years ago, including moons, are now considered possible abodes for alien life.
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Scientists now believe that red dwarf stars, which are eight times as common as stars like our sun, might be able to support planets with life. A planet orbiting a red dwarf star, such as the fictional Aurelia, would always face the star, leaving one side in darkness.
As for the plants and creatures on those planets, Darwinian evolution would probably rule alien life, the scientists concluded. "Otherwise life is too vulnerable," Shostak said.
"You need some variation to adapt, and the moment you have adaptation, you will have selection. That's how nature builds things," he added.
Aurelia and the Blue Moon
On the imaginary Aurelia there would be no seasons, days, or nights. While the dark side would be covered in ice, a life-friendly atmosphere would sustain a landscape of immense rivers and vast flood plains on the light side.
For the TV special, biologists conceived of life-forms that could theoretically survive on Aurelia, including the gulphogs and hysteria. The planet's keystone animal, they speculated, would be the "mudpod," an armadillo-like species that creates a vast network of lagoons that make up the stinger fan forest.
On the Blue Moon, meanwhile, a dense atmosphere and low gravity would make flying a lot more appealing. With carbon dioxide levels 30 times greater than those of Earth's, giant, flat-topped "pagoda trees" may grow half a mile (0.8 kilometer) high.
The scientists didn't rule out the possibility that life could occur in some truly alien chemistry. But they also seem to believe that alien life would be based on carbon and water, as life is on Earth.
"Life as we know it is extremely special and extremely strange and depends on the remarkable properties of carbon and liquid water," said Simon Conway Morris, an evolutionary biologist at the University of Cambridge in England.
"Evidence from evolutionary convergence strongly suggests that, although extraterrestrial [regions that support life] will look alien, deep down they will be quite similar to those on Earth," said Morris, who also appears in the TV special.
Searching the Skies
Although many scientists contend that alien life is inevitable, there is still no proof that other worlds host even the tiniest forms of life.
SETI has for decades been listening for possible radio signals from extraterrestrial life. So far SETI has not heard any messages, but the range of its searches has been limited.
The institute is now building a radio telescope that will be able to examine more than a million star systems.
Still, radio-signal searches would only pick up intelligent life. Several new projects are designed to detect life, intelligent and otherwise, in space.
The European Darwin Project plans to use NASA's upcoming Terrestrial Planet Finder (TPF) space telescopes to scan the heavens for chemical signals that life might give off, such as carbon dioxide, oxygen, methane, and water vapor.
The TPF observatories will probably not be up and running until 2015 or so. NASA's Kepler Mission to find habitable planets, on the other hand, is expected to launch in 2008. It will allow scientists to search for Earth-size worlds in orbit around distant stars.
"This is the century for the discovery of extraterrestrial life," said Conway Morris, the Cambridge biologist. "It is an incredibly exciting time."
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