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Kepler starts mission to detect other Earths

NASA's spacecraft launches successfully, as it begins its three-and-a-half-year mission to discover planets like the one it just left.

Kepler lifts off Friday night in Florida. NASA/Jack Pfaller

The Kepler spacecraft vaulted away from Cape Canaveral late Friday, boosting a powerful space telescope into orbit around the sun for a $591 million mission to search for Earth-like planets orbiting distant stars.

"I think people everywhere want to know whether, with all the stars out there, do they have planets that are Earth-sized?" said principal investigator William Borucki of NASA's Ames Research Center. "Are Earths frequent or are they rare? And this gives us that answer. It's the next step in mankind's exploration of the galaxy."

The Kepler spacecraft's three-and-a-half-year mission began on time at 10:49:57 p.m. local time with a crackling roar and a torrent of fire that briefly turned night into day along Florida's coast.

This was the 339th Delta rocket launched since 1960, the 141st upgraded Delta 2 rocket, and the 86th successful Delta launch in a row dating back to January 1997. The Delta 2 record now stands at 139 successful missions against just two failures.

Engineers will spend about two months checking out and calibrating Kepler's complex systems before the mission begins in earnest.

Trailing the Earth in its orbit around the sun, Kepler will aim a 95-megapixel camera on a patch of sky the size of an outstretched hand that contains more than 4.5 million detectable stars. Of that total, the science team has picked some 300,000 that are of the right age, composition, and brightness to host Earth-like planets. Over the life of the mission, more than 100,000 of those will be actively monitored by Kepler.

The spacecraft's camera will not take pictures like other space telescopes. Instead, it will act as a photometer, continually monitoring the brightness of candidate stars in its wide field of view and the slight dimming that will result if planets happen to pass in front.

By studying subtle changes in brightness from such planetary transits and the timing of repeated cycles, scientists can ferret out potential Earth-like worlds in habitable-zone orbits.

The probability of finding sun-like stars with Earth-like planets in orbits similar to ours--and aligned so that Kepler can "see" them--is about one-half of 1 percent. Given the sample size, however, that still leaves hundreds of potential discoveries.

But it will take three-and-a-half years of around-the-clock observations to capture the repeated cycles needed to confirm detection of an Earth-like world in an Earth-like orbit.

"There's a lot of desire in the science community to understand extraterrestrial planets, not just find them," said Ed Weiler, NASA's associate administrator for space science. "We've already found 300 or so, mostly from the ground. But now we're entering the stage of going beyond just proving that they exist. It's how many are out there, and perhaps the most important question of all, are there any 'Earths' out there?"

The original version of this article by CBS News space consultant William Harwood can be found here.