A NASA spacecraft scanning the sky has discovered a cold failed star that glows green in infrared light and has an atmosphere filled with deadly gases that would make it pretty stinky, too.

The failed star is what astronomers call a brown dwarf, a catch-all category for objects that appear to be too large to be planets, but never attain star-hood. It is one of the coldest brown dwarfs yet found. [New photo of brown dwarf]

Scientists used NASA's Wide-field Infrared Survey Explorer, or WISE, observatory to spot the brown dwarf, which is dim but shines a pale green as a result of the way astronomers process infrared images to make them visible to human eyes.

"The brown dwarfs jump out at you like big, fat, green emeralds," said Amy Mainzer, WISE deputy project scientist at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.

Brown dwarfs look green in WISE images because the methane in their atmospheres absorbs the infrared light that has been coded blue, Mainzer added. Since the objects are also too faint to give off the infrared light that is color-coded red, they show up as green.

Brown dwarfs are made of gas, much of it in the form of methane, hydrogen sulfide and ammonia, and at concentrations that are deadly to humans, and are foul-smelling to boot.

"If you could bottle up a gallon of this object's atmosphere and bring it back to Earth, smelling it wouldn't kill you, but it would stink pretty badly — like rotten eggs with a hint of ammonia," Mainzer said in a statement.

The new brown dwarf

Brown dwarfs are cosmic misfits that start out as collapsing balls of gas, like stars, but they lack the mass to fuse atoms together at their core and shine with starlight.

Over time, brown dwarfs cool off until they can be seen only in infrared light. There may be many such objects lurking in our cosmic neighborhood, but astronomers know of only a handful so far, researchers said.

WISE's new brown dwarf, called WISEPC J045853.90+643451.9, is estimated to be 18- to- 30 light-years away. It has a temperature of about 620 degrees Fahrenheit (327 degrees Celsius), making it one of the coldest brown dwarfs known, researchers said.

The discovery was confirmed by follow-up observations at the University of Virginia's Fan Mountain telescope, the Large Binocular Telescope in southeastern Arizona, and NASA's Infrared Telescope Facility on Mauna Kea, Hawaii.

The research has been detailed an issue of the Astrophysical Journal.

NASA launched the WISE observatory in December 2009 and the brown dwarf was spotted about 57 days into the survey mission. Researchers hope that the swift discovery is a sign that WISE will deliver more.

Ultimately, the WISE observatory may identify hundreds of brown dwarfs and the mission's science team has already racked up a host of candidates that appear similar to the newly discovered one, researchers said.

Cosmic laboratories

To scientists, brown dwarfs provide laboratories for studying planet-like atmospheres.

"They're a great test of our understanding of atmospheric physics of planets, since they don't have solid surfaces, and there's no big, bright sun to get in the way," said study co-author Michael Cushing, a postdoctoral fellow at JPL.

WISE is scanning the whole sky in infrared light, picking up the glow of not just brown dwarfs but also asteroids, stars and galaxies. It has discovered 19 comets and more than 33,500 asteroids so far, sending millions of images down to Earth in the process.

NASA launched the WISE telescope in December 2009 on a 10-month mission to map the entire sky.

The telescope has run out of coolant needed to keep its four infrared detectors from warming up, researchers said. But two of the detectors work well even at warmer temperatures, mission scientists have said.

This article was reprinted with permission from SPACE.com.

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