Heat-Seeking WISE Spacecraft Set to Launch

Infrared instrument promises bonanza of finds, from asteroids to remote galaxies.

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By Ron Cowen, Science News

Veteran astronomer Ned Wright is already considered pretty smart. But soon he’ll be getting wise.

That’s WISE as in Wide-field Infrared Survey Explorer, the NASA spacecraft set for launch on December 11 that will provide the most comprehensive examination of the sky ever recorded in infrared radiation. Wright, of the University of California, Los Angeles, leads the $320 million robotic mission, which for at least nine months will map the sky in four bands of infrared wavelengths. These wavelengths, ranging from 3.3 micrometers to 23 micrometers, are absorbed by Earth’s atmosphere and can’t be seen from the ground.

The mission is expected to catalog hundreds of millions of infrared-emitting bodies, including hundreds of dim, previously unknown asteroids and comets that cross Earth’s orbit. WISE will also give a detailed census of thousands of failed stars, called brown dwarfs, and millions of distant galaxies that glow unusually brightly at infrared wavelengths.

WISE is expected to dramatically boost the number of known debris disks—composed of pulverized rocky remnants of planet formation—around young stars and to turn up more of the dusty cocoons that serve as birth sites for stars. Dust will be easily detected because it absorbs the visible and ultraviolet light from these hatchlings and reradiates the light in the infrared.

The craft is also likely to find the nearest known brown dwarfs—Jupiter-sized balls of gas that are not quite massive enough to keep burning like stars do. Wright calculates that WISE may find as many as 100 brown dwarfs within a mere 20 light-years of Earth. By imaging hundreds of thousands of asteroids in the main belt between the orbits of Mars and Jupiter, WISE will provide the first complete census of the number and sizes of these rocky bodies and new information about their composition, Wright says.

“I’m very excited because we’re going to be seeing parts of the universe that we haven’t seen before,” he notes.

Wright views the mission as the successor to the Infrared Astronomical Satellite, which in 1983 became the first craft to survey the entire sky in the infrared. WISE is 500 times more sensitive than IRAS was at the mid-infrared wavelengths of 12 micrometers and 23 micrometers, meaning that the new craft will record much fainter infrared sources and pinpoint their locations with much greater accuracy.  

Researchers still use data generated by the now-defunct IRAS to guide high-resolution observations by large infrared telescopes. In the same way, WISE, which relies on a relatively small 40-centimeter telescope, is expected to provide an avalanche of data to help target searches by much larger telescopes, such as the recently launched European Space Agency’s Herschel telescope and especially the James Webb Space Telescope, the proposed infrared successor to the Hubble Space Telescope.

“IRAS was the gift that just kept on giving, and I think WISE will do the same,” comments Charles Beichman of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “When you make a breakthrough of hundreds to thousands in sensitivity, great things will follow. When you do that over the whole sky, it will be referenced for decades to come.”

The craft will settle into a polar orbit around Earth, allowing WISE to sweep out a circle that will slowly precess, or change its angle of inclination. That orbit will enable WISE, which takes a snapshot every 11 seconds, to scan the entire sky in six months. The craft will then begin a second, partial scan of the sky that will last three months.

A tank of hydrogen ice will keep WISE chilled to 15 degrees above absolute zero, reducing infrared emissions from the craft that could interfere with detection of faint infrared sources from space. Wright expects the first images to be released a few months after launch, but he says the first detailed maps won’t be available until sometime around April 2011.

Photo credit: NASA/JPL.


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