Distant and dim, the brown dwarf WISE J085510.83-071442.5 (snappy name, there) could well have passed unnoticed since it's not large enough to ignite nuclear fuel to radiate visible light.

However, NASA's WISE (Wide-field Infrared Survey Explorer) has spotted it, and further work by the Spitzer Space Telescope yielded a surprise: it's the coldest brown dwarf discovered so far, with a surface temperature of between -48 and -13°C, or -54 and -9°F.

At 7.2 light years distant, it's nearly twice as far away as our nearest neighbour Alpha Centauri, but in astronomical terms, it's still pretty intimate with our system – it's the fourth-closest object to the solar system so far identified.

The combination of its infrared light, which of course is what WISE looks for, plus its relatively quick motion across the sky – a function of its proximity – are what made it possible for the object to be spotted, NASA says.

Pennsylvania State University astronomer Kevin Luhman spotted the motion in March 2013, and then analysed images taken Spitzer and by the Gemini South telescope in Chile. The additional data yielded the surprisingly cold temperature of the object, as well as a fix on its distance.

NASA's animation of the object, combining WISE and Spitzer images

Luhman is quoted in the release as saying “It's very exciting to discover a new neighbor of our solar system that is so close. And given its extreme temperature, it should tell us a lot about the atmospheres of planets, which often have similarly cold temperatures.”

At between 3 and 10 times the mass of Jupiter, WISE J085510.83-071442.5 is also one of the least massive discovered so far, small enough that there's a chance it's a gas giant planet similar to Jupiter that's been ejected from its system. However, since brown dwarfs are far more common, that's the explanation preferred by Luhman. ®