As the number of known exoplanets grows, habitability is one of the main things we look for, and planets like Wolf 1061c or those in the TRAPPIST system are some of the best candidates. But exoplanets that are completely and utterly uninhabitable still have plenty to teach us, and NASA has just found a Jupiter-like planet that we're going to crown Least Likely To Host Life: KELT-9b, a blistering gas giant that's hotter than most stars.
The most common stars in the Milky Way are red dwarfs, which bubble away at a relatively cool temperature of less than 4,000 K (3,727° C, 6,740° F). KELT-9b, meanwhile, has surface temperatures of up to 4,600 K (4,327° C, 7,820° F) on its dayside, which is tidally locked to face its host star. That makes the gas giant not just a "hot Jupiter," but the hottest Jupiter – or any other planet, for that matter – ever found.
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"It's a planet by any of the typical definitions of mass, but its atmosphere is almost certainly unlike any other planet we've ever seen just because of the temperature of its dayside," says Scott Gaudi, lead author of the study.
KELT-9b is almost three times more massive than our own Jupiter but only half as dense, orbiting a blue A-type star called KELT-9. Twice as hot and large as the Sun, this star is bombarding KELT-9b with UV radiation that's causing its atmosphere to swell up. It may even be evaporating the planet, causing KELT-9b to leave a tail trailing behind it like a comet.
It doesn't help its habitability that KELT-9b orbits extremely close to its star, with one year lasting about a day and a half. And if it's still not weird enough, the planet orbits the "wrong" way. Whereas most planets circle their stars along a horizontal plane, in the same direction that the star spins, KELT-9b orbits perpendicular to KELT-9's spin, which could make it appear to be moving vertically.
KELT-9b was discovered about a year ago using the Kilodegree Extremely Little Telescope (KELT), and in future more could be learned about the unusual system by studying it with telescopes like Spitzer, Hubble and the upcoming James Webb Space Telescope. These observations could help spot KELT-9b's comet-like tail, and judge how long the stressed out planet has left to live.
"Thanks to this planet's star-like heat, it is an exceptional target to observe at all wavelengths, from ultraviolet to infrared, in both transit and eclipse," says Knicole Colon, co-author of the study. "Such observations will allow us to get as complete a view of its atmosphere as is possible for a planet outside our solar system."
The research was published in the journal Nature.