NASA has launched a space telescope that will probe the skies for planets similar to the Earth. A rocket carrying the craft lifted off late Friday to begin a three-and-a-half year mission.
NASA engineers created the Kepler mission to study the question of whether or not the Earth is the only planet of its kind in the universe. The $600 million project is named after the 17th century German astronomer who helped describe how planets moved in orbits around stars.
NASA associate administrator for science, Ed Weiler, says the mission was born of the age-old curiosity about life outside our solar system.
"It very possibly could tell us that Earths are very very common," he said. "We have lots of neighbors out there. Or it quite possibly could tell use that Earths are really, really rare. Perhaps we are the only Earth."
Astronomers first discovered planets orbiting around stars outside our solar system in 1995. Since then, more than 300 others have been found, but many are gas giants that are unlikely to support life.
The project's principal scientist, Bill Borucki, says Kepler is intended to focus on smaller, rocky planets with conditions similar to Earth.
"What we want is a temperature that is just right, not too hot, not too cold. Just right for liquid water on the surface, where life might evolve," he said.
Once in orbit, the Kepler telescope will point toward one portion of the Milky Way, to study some 100,000 stars. It is intended to track the stars over a long period of time, in an effort to detect any changes in brightness. Scientists say a dimming star could be the sign of a planet passing between the star and the telescope.
Mission scientist Natalie Batalha says one problem is that the orbit of some planets may prevent them from being detected in this manner.
"It's a numbers game," she said. "We need to observe lots and lots of stars because the probability of a geometric alignment is very small, something like one to 10 percent."
Scientists say the mission should begin to yield important data by the end of Kepler's
lifespan in three and a half years. But they say the research will go on after that, to continue studying whether life is really present on other planets similar to Earth.