The first spacecraft dedicated to finding potentially habitable planets beyond our solar system

NASA's planet-hunting telescope, Kepler, rocketed into space Friday night on a historic voyage to track down other Earths in a faraway patch of the Milky Way galaxy.

It's the first mission capable of answering the age-old question: Are other worlds like ours out there?

The spacecraft launches Friday night to embark on the most exhaustive hunt for a potentially habitable planet beyond our solar system.
NASA's Kepler seeks another Earth among the stars.The first spacecraft dedicated to finding potentially habitable planets beyond our solar system is poised to blast off from Cape Canaveral tonight on a three-year mission to probe 150,000 stars in the most sweeping hunt for Earthlike objects ever undertaken by NASA.
The Delta II rocket, carrying the widest-field telescope ever put in space, lifted off the launch pad at Cape Canaveral at 10:49 p.m. Eastern time.
The launch vehicle headed downrange, gathering speed as its three stages ignited, one after the other, passing over the Caribbean island of Antigua and tracking stations in Australia before climbing into orbit.

Kepler will eventually settle down to scan tens of thousands of stars near the constellations Cygnus and Lyra in search of planets where water could exist on the surface in liquid form, a key condition for life as we know it.

"We have a feeling like we're about to set sail across an ocean to discover a new world," said project manager Jim Fanson of the Jet Propulsion Laboratory in La Cañada Flintridge. "It's sort of the same feeling Columbus or Magellan must have had."

The $590-million Kepler mission is jointly managed by JPL and NASA's Ames Research Center in the Bay Area. The spacecraft carries a 15-foot-long telescope with a 55-inch mirror that can scrutinize a wide star field for the telltale dimming of starlight that occurs when a planet crosses in front of it, known as a transit.

Over the last decade, scientists have employed the same technique with ground-based telescopes to discover 340 planets circling other stars. But because the optics of ground-based instruments are compromised by atmospheric interference, most of the planets found so far are Jupiter-like gas giants that orbit so close to their parent stars that any life forms would be incinerated.

The scientists expect to find hundreds of planets during the mission, scheduled to last more than three years. But even with the telescope's wide field of vision, it will be no easy task for Kepler to find smaller, Earth-like planets. Scientists have calculated that the change in brightness caused by such a planet transiting its star will be only about 0.008%, or about 84 parts per million. On top of that, there is less than one chance in 100 that a planet circling a far-off star will be aligned in just the right way for Kepler to spot a transit.

A final complication is that not all dimming is caused by transits. Sunspots on the surface of a star are cooler areas linked to an increase in magnetic activity. They also cause the star's light to dim. But Kepler scientists said they think they understand the signature of sunspots well enough to deal with that problem.

For a planet to become a candidate for the first Earth-type planet around another star, Kepler must measure at least three separate transits, scientists said. If the team is uncertain about some measurements, or simply wants more observing time, the mission could be extended to six years, NASA said.