The hottest planet is tearing itself apart
Temperatures are so extreme that the world’s atmosphere is fiercer than some stars
The hottest planet ever discovered is so overheated that it is tearing apart its own atmosphere, according to a recent study using the Spitzer Space Telescope.
The planet, KELT-9b, is an ultra-hot Jupiter, meaning it’s a gas giant orbiting close to its star – it takes just one and half days to orbit. The proximity means the world is tidally locked, with one side always facing its star.
The planet was discovered in 2017 by the Kilodegree Extremely Little Telescope (KELT) and it was immediately apparent that the world’s atmosphere must be extremely hot. A team of astronomers quickly sought time on NASA’s Spitzer Space Telescope to create a map of the planet’s temperature in infrared.
Spitzer observed KELT-9b at several points during its orbit, when different parts of the planet were facing Earth, allowing astronomers to build up a global picture of how heat is distributed across the planet. They discovered that dayside temperatures reach 4,300˚C, making it the warmest planet on record and hotter than some stars.
“This kind of planet is so extreme in temperature, it is a bit separate from a lot of other exoplanets,” says Megan Mansfield from the University of Chicago, who led the study.
The map showed that the nightside was cooler than the dayside but not by much, meaning there are wind currents mixing the atmosphere between the two. The team also found the dayside temperatures are high enough to dissociate the hydrogen, where the bond between two atoms in a hydrogen molecule breaks. When the dissociated atoms flow around to the nightside, the temperatures are cool enough for them to recombine, only for the planetary wind to blow the newly rejoined molecules round to the dayside to be torn apart again.
“There are some other hot Jupiters and ultra-hot Jupiters that are not quite as hot but still warm enough that this effect should be taking place,” says Mansfield.
Astronomers will continue to study the planet to understand how the effects of this dissociation and recombination balances out with the flow of heat around the planet in an effort to understand these most extreme worlds.
http://www.spitzer.caltech.edu