Billions and billions of stars…
Does this discourage alien hunters? Not at all, says Tarter, who notes that the Milky Way alone may contain as many as 400 billion stars.
Concluding there is no extraterrestrial life based on current data, she says, is equivalent to "deciding that the ocean has no fish on the basis of one glass of water."
Tarter also points to discoveries of more Earth-like planets, as well as evidence of water on Mars and "extremophiles" here on Earth. Extremophile organisms, she explains, can survive and even thrive at the bottom of the ocean, in nuclear reactor waters and in pure salt crystals.
"It appears that there's more habitable real estate than we once thought," Tarter says, which suggests planets previously thought too hostile might actually be capable of hosting life.
But researchers such as Robin Hanson of George Mason University in Fairfax, Va., wonder whether the big picture really looks so promising when it comes to advanced life. Hanson supports SETI but finds it telling that humans haven't come across anything yet.
"It has been remarkable and somewhat discouraging," Hanson says, "that the universe is so damn big and so damn dead."
Seeking the 'Jodie Foster experience'
But if life does, or did, exist elsewhere, STScI's Livio suggests that finding elementary proof of it might be possible within 30 years and that Mars could give up more secrets before then.
As far as how we'll find alien life, Livio says, "I will be thrilled if SETI gets there, but I will be amazed if they do." He suggests that "baby steps" of research — a slow progression from finding more Earth-like planets to investigating their atmospheres and looking for signs of rudimentary life — will more likely generate results.
Biochemist Steve Benner of the Foundation for Applied Molecular Evolution agrees. "No one will be more astonished than me if we have a Jodie Foster experience," he says, referring to Contact, in which the actress plays an astronomer who deciphers a signal broadcast from deep space.
In any event, SETI's Shostak points out that finding Antarctica and the Northwest Passage on Earth took more time than we've spent searching all of space for other forms of life. So, he says, maybe we just haven't looked enough yet.
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