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WISE mission completes first glance through universe
BY STEPHEN CLARK
SPACEFLIGHT NOW

Posted: July 18, 2010


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The WISE infrared telescope finished surveying the universe Saturday, but its $320 million mission will continue until its funding and hydrogen coolant run out later this year.


WISE captured this mosaic of the Pleiades star cluster in a web of cold dust. Credit: NASA/JPL-Caltech/UCLA
 
Launched from California last December, NASA's Wide-field Infrared Survey Explorer has slowly scanned the sky since January, uncovering faraway galaxies, stars and dark asteroids that could threaten Earth.

"Like a globe-trotting shutterbug, WISE has completed a world tour with 1.3 million slides covering the whole sky," said Edward Wright, mission's principal investigator at the University of California, Los Angeles.

WISE is designed to find unseen luminous galaxies, ultra-cool brown dwarfs, and asteroids beyond the observing limit of ground telescopes.

It has already spotted 25,000 new asteroids, most of them in the main belt between Mars and Jupiter, but more than 90 of WISE's asteroid discoveries are on tracks that could threaten Earth.

WISE has also tracked more than a dozen new comets traveling in the distant solar system, according to NASA.

"WISE is filling in the blanks on the infrared properties of everything in the universe from nearby asteroids to distant quasars," said Peter Eisenhardt, project scientist for WISE at the Jet Propulsion Laboratory in Pasadena, Calif. "But the most exciting discoveries may well be objects we haven't yet imagined exist."

The six-month survey wrapped up Saturday, but it will map half the sky again until WISE runs out of chilly solid hydrogen cooolant.

WISE's infrared detectors are kept inside a hydrogen-filled cryostat, exposing parts of the telescope to frigid temperatures as low as 8 Kelvin, or -447 degrees Fahrenheit.

But the frozen hydrogen is gradually sublimating, or turning from a solid to a gas, putting WISE's sky scans on the clock. The spacecraft launched with about 35 pounds of hydrogen, and the latest estimates show WISE will run out sometime in November, slightly later than expected, according to Wright.

"The predicted lifetime has grown a bit, so we now anticipate lasting until November," Wright said.


Artist's concept of the WISE spacecraft. Credit: NASA/JPL-Caltech
 
WISE should see half the sky again by November, according to NASA. Officials plan to end the mission when the coolant is gone, meaning WISE will complete one-and-a-half surveys of the infrared universe.

The satellite takes pictures of the sky in strips as it circles Earth, and the planet's orbit around the sun exposes WISE to different parts of the universe.

Wright and other mission scientists proposed continuing the WISE mission after November, when the satellite's 16-inch telescope could still observe the universe in two of its four wavelengths, even without the hydrogen cooling agent.

The telescope's focal plane is predicted to rise to 72 Kelvin, or -330 degrees Fahrenheit, once the hydrogen sublimates. Scientists say WISE could still view the universe in near-infrared light at such temperatures.

The so-called "warm phase" proposal would have extended WISE's mission for three more months, permitting the satellite to finish its second all-sky survey with half its imaging power.

But NASA's 2010 Astrophysics Senior Review Committee recommended not funding the extended mission, saying it was "impressed with the promise of the cryogenic mission" but "did not find adequate scientific justification in the proposal for the cost" of the warm phase operations.

"We are not planning a warm phase," Wright told Spaceflight Now. "But we are discussing several decommissioning options."

Wright did not discuss the decommissioning options or say whether WISE could continue some observations past November.

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