Are there lively, Earth-like planets out there somewhere?
That question, once only the subject of science fiction, has become a major theme of serious astronomers who believe the answer may be only a few years beyond their grasp.
For decades, the search for planets orbiting distant stars was considered a nutty backwater of astronomy. With false reports and embarrassments, most astronomers avoided the subject.
Detecting Wobbly Stars
All of that has changed in the last five years. Planet-hunting astronomers have now found more than 50 planets, all Jupiter-sized or larger, and engineers and scientists are designing instruments and missions that will not only search for Earth-sized objects, but even analyze for the chemistry of life.
More than 400 astronomers attending the national meeting of the American Astronomical Society to hear researchers discuss the techniques for searching the universe for other Earths and for life.
"Planet finding has become an acceptable science," said NASA's top scientist, Ed Weiler, who called the conference "a real watershed."
Astronomers now call it the "terrestrial planet finder" project and talk openly and often about the possibilities that somewhere, among the billions of stars within the hundreds of billions of galaxies, there is another Earth teeming with life.
"You can imagine life existing only on Earth, or in only a few places, or you can imagine that its exists in every cranny of the universe," said Anne Kinney, a NASA scientist. "We may be the generation that finds out."
Finding Jupiter-sized planets, although difficult, is child's play compared with directly detecting a planet the size of Earth orbiting a star 10 to 50 light years away. An Earth-sized planet is simply too small and its host sun too bright. Detecting such a planet indirectly, by measuring the wobble of the star, is impossible with current instruments.
"Trying to find an Earth around a star is like trying to see a firefly around a searchlight when you are looking from Moscow toward Washington," said Weiler.
But experts believe it can be done with instruments and techniques now being developed.
At least four teams, working under a NASA contract, have come up with plans for spacecraft and instruments that could detect planets out to 50 light years and then analyze the light reflected from those planets to search for life.
Looking Close for Life
The plans could include an array of space telescopes, sent to a neutral gravitational point 600,000 miles away from Earth. By flying in formation and taking coordinated images of stars, the combined vision would be of an unprecedented sharpness.
"After we detect a planet, we want to be able to take apart the spectrum of the light and figure out the molecules that are in the atmosphere," said M. C. Noecker of Ball Aerospace, one of the contractors developing terrestrial planet-finder technology.
"We want to be able to test for carbon dioxide, water and oxygen," said Noecker. "If we see all three, then that would be an excellent indication of life on that planet."
Such a mission could be mounted by 2015, say experts, if earlier projects, already planned, prove the technology.
Weiler said a mission called Starlight will test the technique of formation-flying telescopes. It is set for a 2005 launch. Another mission, called the SIM, will launch in 2009 and conduct a systematic search for planet-hosting stars out to 100 light years, or some 600 trillion miles. Still other test missions are planned.
"This is a stepping-stone approach," said Weiler, noting that no final design has been sketched out for the ultimate life-searching mission.
"Right now, we are paying to people to think about terrestrial planet finders," he said. Now that the search is considered legitimate science, said Weiler, "there are a lot of ideas churning around out there."