The Kepler telescope "We won't find E.T., but we might find E.T.'s home"

NASA launched its Kepler spacecraft just before 11 p.m. Friday in a mission that the agency says may fundamentally change humanity's view of itself.

The Kepler spacecraft blasted into space on top of a Delta II rocket from Cape Canaveral Air Force Station in Florida.

The telescope will search our corner of the Milky Way galaxy for Earth-like planets.

"This is a historical mission. It's not just a science mission," NASA Associate Administrator Ed Weiler said during a prelaunch news conference.

"It really attacks some very basic human questions that have been part of our genetic code since that first man or woman looked up in the sky and asked the question: Are we alone?"

Kepler contains a special telescope that will stare at 100,000 stars in the Cygnus-Lyra region of the Milky Way for more than three years as it trails Earth's orbit around the Sun.

The spacecraft will look for tiny dips in a star's brightness, which can mean an orbiting planet is passing in front of it -- an event called a transit.

The instrument is so precise that it can register changes in brightness of 20 parts per million in stars that are thousands of light years away.

"Being able to make that kind of a sensitive measurement over a very large number of stars was extremely challenging," Kepler project manager James Fanson said.

"So we're very proud of the vehicle we have built. This is a crowning achievement for NASA and a monumental step in our search for other worlds around other stars."

"We won't find E.T., but we might find E.T.'s home," said William Borucki, science principal investigator for the Kepler mission.