Earth-hunter telescope

Earth-hunter telescope prepared for launch

NASA unveiled a modest telescope with a sweeping mission to discover if there are any Earth-type planets orbiting distant stars.

Though astronomers have found more than 330 planets circling stars in other solar systems, none has the size and location that is believed to be key to supporting life. Named after the 17th century astronomer who figured out the motions of planets, Kepler is scheduled for liftoff on March 5 aboard an unmanned Delta 2 rocket from the Cape Canaveral Air Force Station.

Once in position trailing Earth in orbit, Kepler will spend at least 3 1/2 years focused on a star-rich patch of sky between the constellations Cygnus and Lyra.

Equipped with a 95 megapixel camera the largest ever flown in space Kepler will attempt to find Earth-sized planets flying across the face of their parent stars.

Scientists say it will be a bit like trying to spot a gnat in the glare of a floodlight.

To an outside observer, a planet as large as Jupiter temporarily blots out about 1% of visible light from the sun as it makes its transit. Passage of Earth-like worlds produce a change in brightness of about 84 parts in a million.

Kepler will need to keep extraordinarily still for weeks at a time, breaking its gaze only once a month for 12-hour radio linkups with Earth. Data from 170,000 target stars will be relayed for scientists on the ground to analyze.

The selected stars are just a fraction of the estimated 4 million objects that will fall within Kepler's view, but scientists want to maximize the telescope's observing time to make sure they catch as many blinking stars as possible.

To find a planet like Earth, scientists will need to catch at least four transits, a process that will take about 3 1/2 years. Ground-based telescopes will be used to verify results.

No one knows how many stars have solid-body planets like Earth orbiting in what are called habitable zones, places where liquid water can exist.

Water is believed to be crucial for life, although that evidence is based on a sample of one Earth.