Let's all welcome the new kid on the solar block.
Artist's interpretation of a brown dwarf. Image via Tyrogthekreeper
Friday, NASA announced the discovery of WISE J085510.83-071442.5, a brown dwarf located 7.2 light-years away. The object—which we'll abbreviate to WISE 0855–0714—has edged out the red dwarf Wolf 359 to become the fourth closest system to our Sun.
“It's very exciting to discover a new neighbor of our solar system that is so close," Kevin Luhman, an astronomer at Penn State's Center for Exoplanets and Habitable Worlds, said in a statement. "Given its extreme temperature, it should tell us a lot about the atmospheres of planets, which often have similarly cold temperatures.”
Luhman has been hunting for brown dwarfs for decades, and has located several of them using the Wide-field Infrared Survey Explorer and the Spitzer Space Telescope. In fact, this isn't even the first time he's bumped our nearest neighbors back a spot in line. Just last year, he discovered a brown dwarf binary system only 6.5 light-years away, making it the third closest system to the Sun. The Luhman 16 system now bears his name.
Our nearest neighbors. Image via NASA/Penn State.
But this most recently discovered dwarf is a little different from the binary system, and not just in nomenclature. For example, the weather forecast on Luhman 16B calls for pretty consistent molten iron rain showers, whereas WISE 0855–0714 is a bonafide ice queen. In fact, it's the coldest brown dwarf ever found, with an estimated temperature of 225–260 kelvins (9 degrees Fahrenheit, or -13 degrees Celsius). The record-holders up until this point at least had the decency to remain at room temperature.
How could a star possibly be so cold? The answer is that brown dwarfs are total celestial iconoclasts, suspended halfway between being real stars and beefed-up gas giants. Indeed, many astronomers argue that these dim orbs should simply be categorized as Super-Jupiter planets (by the way, when are we going to start calling them Supiters already?).
They have a point—brown dwarfs can't even perform nuclear fusion to produce starlight. That's pretty much the basic qualification you need to be considered a star, and it's the reason why it's impossible to spot brown dwarfs in any wavelength shorter than infrared (though they mysteriously spit up X-Rays occasionally). On top of that, these worlds are more or less planet-like in scale, with WISE 0855–0714 only clocking in at around three to ten times the mass of Jupiter. The Kepler Space Telescope has discovered plenty of exoplanets bigger than that.
However, another camp of astronomers argues that since brown dwarfs are born out of collapsing molecular clouds like stars—not in accretion discs like planets—they should remain their own distinct category. All this is to say that the classification of brown dwarfs is as murky as the objects themselves, and basically depends on whether you consider an object's formation to be more important than its interior physics.
Regardless of whether WISE 0855–0714 is considered a star, a planet, or something in between, its discovery is welcome news for space enthusiasts. "It is remarkable that even after many decades of studying the sky, we still do not have a complete inventory of the sun's nearest neighbors," said Michael Werner, who runs the Spitzer Space Telescope in a statement. "This exciting new result demonstrates the power of exploring the universe using new tools, such as the infrared eyes of WISE and Spitzer."