Infrared telescope to detect dim, dusty objects

LOS ANGELES (Reuters) - NASA plans next month to launch a space telescope that will scan the heavens for the infrared glow of celestial objects never seen because they are too dim, dusty or distant, scientists said on Tuesday.

The Wide-field Infrared Survey Explorer, or WISE, is expected to reveal hundreds of thousands of dark asteroids lurking undetected in the solar system, and millions of elusive stars and galaxies farther out in space.

The spacecraft, to be carried into orbit by a Delta 2 rocket, will roll out to its launch pad at Vandenberg Air Force Base in California on Friday for a liftoff slated for as early as December 9, managers of the $320 million project said at a news briefing in Washington, D.C.

Its six-month mission is to survey the entire sky for infrared radiation, a form of light invisible to the human eye but emitted from the coldest of objects, including those overlooked by telescopes sensitive only to visible light.

"We expect certainly to see many asteroids, stars and galaxies," said Edward Wright of the University of California, Los Angeles, the mission's principal investigator. "But really I'll be surprised if I'm not surprised ... because we're going to find things that nobody has imagined yet."

The telescope sits in a tank filled with frozen hydrogen that chills it to just slightly above absolute zero, the coldest temperature theoretically attainable, thus preventing the instrument from picking up its own infrared heat.

Among the phenomena WISE is likely to uncover is a large number of failed stars called brown dwarfs -- balls of gas many times smaller than the sun that lack sufficient mass to trigger their own internal stellar engines. Optically invisible, they glow in the infrared spectrum.

Brown dwarfs are believed to be more numerous than actual stars in the nearby universe, and some may reside even closer to Earth than the nearest known star, Proxima Centauri, about 4 light years away, said Peter Eisenhardt, chief project scientist at NASA's Jet Propulsion Laboratory. Both theories are likely to be confirmed by WISE.

Infrared light also penetrates dust, enabling WISE to both illuminate and peer through the dense, invisible haze that obscures some of the most distant galaxies in the cosmos.

A class of such objects called ultra-luminous galaxies, thought to be super-incubators of new stars, shine with more than a trillion times the light of the sun. But most of that light is emitted as infrared, Eisenhardt said.

"So we're going to find the most super-duper, hyper ultra-luminous galaxies in the universe and find just how extreme these galaxy-forming processes can get," he said.

Scientists say the spacecraft's detectors are about 500 times more sensitive than those of the last infrared sky survey in 1983, a joint European-NASA mission.

Closer to home, WISE will likely add several hundred hidden asteroids and comets to the known inventory of "near-Earth objects" whose orbits come perilously close to Earth's orbit, while telling scientists more about their composition.

(Editing by Dan Whitcomb and Eric Beech)