Planet-Hunting Spacecraft Beams Home First Images

This story was updated at 8:09 p.m. EDT.

The planet-seeking Kepler spacecraft has beamed home its first images of a patch of the sky where NASA hopes to find Earth-like planets circling distant, alien stars.

Some 14 million stars are estimated to lurk within the first views from Kepler, which NASA released Thursday. The images reveal a swath of stars between the constellations Cygnus and Lyra that fill an expansive area of our Milky Way galaxy which, when seen from Earth, is about the size of human hand held up against the night sky at arm's length.

"It's thrilling to see this treasure trove of stars," said William Borucki, Kepler?s science principal investigator at NASA's Ames Research Center in Moffett Field, Calif. "We expect to find hundreds of planets circling those stars, and for the first time, we can look for Earth-size planets in the habitable zones around other stars like the sun."

The so-called ?habitable zone? around a star is a belt in which liquid water could exist on the surface in lakes, rivers or oceans. Too close to its stellar parent and a planet would be too hot, while an orbit too far out would yield only a frozen world, NASA scientists have said.

The first images from Kepler released by NASA include views of its entire target zone, as well as up-close shots that zoom in on only a fraction of the full star field. One view includes a cluster of stars some 13,000 light-years from Earth known as NGC 6791, while another image includes a star called Tres-2, which is already known to harbor a massive Jupiter-like planet close by.

"Kepler's first glimpse of the sky is awe-inspiring," said Lia LaPiana, NASA?s Kepler's program executive at NASA?s headquarters in Washington, D.C. "To be able to see millions of stars in a single snapshot is simply breathtaking."

NASA launched the $600 million Kepler spacecraft last month to sift through those millions of targets for 100,000 pre-selected candidate stars that may have Earth-sized planets around them. Those target stars sit between 600 and 3,000 light-years from Earth. The spacecraft was built by Ball Aerospace in Boulder, Colo., and is slated to last at least 3 1/2 years.

At Kepler?s heart is a 95-megapixel camera, the largest ever launched into space, which the spacecraft will use to hunt for Earth-like planets. Astronomers have discovered more than 300 extrasolar planets to date, but most of them are massive gas giants the size of Jupiter or larger.

Kepler spacecraft is expected to identify new extrasolar planets by casting an unblinking stare at its target star field. Its sensitive camera will record the tell-tale dip in light created by a planet as it crosses in front of its parent star as seen from Earth. While researchers expect to discover a wide range of new planets with Kepler, it?s those rocky worlds the size of Earth that they are most eager to find.

"Everything about Kepler has been optimized to find Earth-size planets," said James Fanson, Kepler's project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Our images are road maps that will allow us, in a few years, to point to a star and say a world like ours is there."

Last week, the spacecraft popped the protective lid off its delicate telescope optics and photometer to prepare for its planet search. Mission managers and scientists plan to spend the next few weeks calibrating Kepler?s photometer and alignment before beginning their hunt for Earth-like worlds in earnest.

"We've spent years designing this mission, so actually being able to see through its eyes is tremendously exciting," said Eric Bachtell, the lead Kepler systems engineer at Ball Aerospace.

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