The $600 million Kepler Spacecraft, named for the 16th-century German astronomer Johannes Kepler, will keep its lens fixed on a patch of sky between the constellations Cygnus and Lyra, staring at about 100,000 stars.
The telescope will not be searching for signs of alien life. It will, however, be looking for the type of temperate Earth-like planets that could be conducive to life. Those planets would be orbiting their stars in the "not too hot, not too cold" sweet spot that Earth orbits the sun.
"We certainly won't find E.T., but we might find E.T.'s home by looking at all of these stars," Bill Boruki, Kepler's principal scientist, told reporters at a press conference Thursday, according to the Associated Press.
It was less than 15 years ago, in 1995, that scientists detected the first planet of any kind orbiting a star other than the Sun. Since then they have found 340 others, but most have been gas giants like Jupiter, orbiting close to their stars at distances that would make for boiling-hot surfaces.
However, that doesn't mean planets that orbit stars more distantly, like Earth, don't exist. But it's difficult to find them -- the main method used to discover distant planets involves measuring their gravitational pull on their star, and that pull is stronger and easier to observe for closely orbiting planets.
Kepler will use a different method entirely. The spacecraft is equipped with a 95-million-pixel digital camera. The camera will stare constantly at the same group of stars, measuring subtle variations in light. Scientists will be looking for the tiny flicker that indicates that a planet is passing in front of the star.
"It's akin to measuring a flea as it creeps across the headlight of an automobile at night," NASA project manager Jim Fanson said, according to AP.
The researchers will be able to deduce the size of the planet from the amount of the star's dimming, and the timing of the planet's orbit by how often the star dims.
Borucki said that the researchers will wait to observe three dimming cycles before they announce that they have found a star.
"When we make a discovery we want it to be bulletproof," he said, according to the New York Times.
That means that confirming the detection of an Earth-like planet, which would take about a year to orbit its star, could take as long as three years.
Ed Weiler, NASA's associate administrator for space, said that the mission will help answer the age-old question of whether other Earth-like planets exist -- and he didn't leave much doubt as to what he hoped the answer would be.
"It very possibly could tell us that Earths are very, very common, that we have lots of neighbors," he said, according to Reuters. "Or it could tell us that Earths are really, really, really rare -- perhaps we're the only Earth. I think that would be a very bad answer because I, for one, don't want to live in an empty universe where we're the best there is. That's a scary thought to many of us."