The Kepler telescope was launched into space Friday night from Cape Canaveral, on its way to search for other Earth-like planets.
The planet-hunting telescope, named Kepler after the German 17th-century astrophysicist, blasted off aboard a Delta II rocket at 10:49 p.m.
It is scheduled to spend 3½ years staring at roughly 100,000 stars, measuring their brightness and any winks in the light that might signify orbiting planets.
"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, said Thursday. (Listen to CBC Radio's Quirks and Quarks interview with Dr. David Koch, the deputy principal investigator on the Kepler mission.)
Ed Weiler, NASA's associate administrator for science, said Kepler is not just another science mission.
"It very possibly could tell us that Earths are very, very common — that we have lots of neighbours out there — or it could tell us that Earths are really, really, really rare," Weiler said at a news conference.
"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."
Kepler will be scouting for Earth-size planets circling stars in the so-called habitable or Goldilocks zone. That's where planets are neither too close nor too far from their star, and where conditions could be ripe for liquid water on the surface.
The search will be on for planets "that are not too hot, not too cold, but just right," Boruki said.
Once launched, Kepler will trail the Earth in an orbit around the sun. It will peer continuously at a large patch of sky near the Cygnus and Lyra constellations, looking for any winks against the brightness of the stars that could indicate passing planets.
The stars to be observed by Kepler are between 600 and 3,000 light years away.
Project manager Jim Fanson of NASA's Jet Propulsion Laboratory in Pasadena, Calif., said the level of precision needed to measure those winks is incredibly high.
"It's akin to measuring a flea as it creeps across the headlight of an automobile at night," Fanson said.
Over the past decade and a half, more than 300 planets have been found to be orbiting stars outside our solar system. But these are largely gas giants like Jupiter. Kepler is designed to zero in on smaller, rocky, Earth-like planets.
Scientists stress that Kepler — about 4.5 metres tall and three metres in diameter — will not be looking for life but rather potentially habitable planets. The mission will cost US$600 million, from start to finish.
The launch comes on the heels of a failed flight of a NASA science satellite from California, the Orbiting Carbon Observatory, just over a week ago.
It used a different rocket than the one for Kepler. Nonetheless, engineers pored over every detail to find any similarities, delaying Kepler's launch by a day.