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This planet is so hot it tears apart the hydrogen molecules in its atmosphere

The extreme forces acting on huge planets close to blistering stars lead to unexpected findings like planets shaped like footballs, planets in strange locations, and even a planet that is hotter than most stars. This last finding, the exoplanet KELT-9b, was the target of more research that revealed it is “prone to planetwide meltdowns so severe they tear apart the molecules that make up its atmosphere,” according to NASA.

KELT-9b is three times the mass of Jupiter and has an almost unbelievable surface temperature of 7,800 degrees Fahrenheit (4,300 degrees Celsius), making it the hottest planet discovered so far. It is this extreme heat that leads to the breakdown of molecules of hydrogen in its atmosphere.

Artist's rendering of a
Artist’s rendering of a “hot Jupiter” called KELT-9b, the hottest known exoplanet — so hot, a new paper finds, that even molecules in its atmosphere are torn to shreds. Credit: NASA/JPL-Caltech
The meltdown takes place on the side of the planet facing the star, called the dayside, with hydrogen molecules being ripped apart and flowing over to the side of the planet facing away from the star, called the nightside, and reforming there before flowing back to the dayside to be destroyed once more.

“This kind of planet is so extreme in temperature, it is a bit separate from a lot of other exoplanets,” Megan Mansfield, a graduate student at the University of Chicago and lead author of a new paper revealing these findings, said in a statement. “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.”

To search for other exoplanets that may have similar phenomena occurring, scientists will need to use highly accurate instruments. Investigating the atmospheres of exoplanets is not easy, but it is possible using tools like NASA’s Spitzer space telescope which captures subtle variations in heat given off by exoplanets by looking in the infrared wavelength.

Using Spitzer data, Mansfield’s team was able to see the difference between the dayside and the nightside of KELT-9b, despite it orbiting so close to its star that one year on the planet only takes one and a half Earth days.

Located 670 light-years away with a surface temperature hot enough to split molecules into pieces, NASA confirmed that “KELT-9b will stay firmly categorized among the uninhabitable worlds.”

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Georgina Torbet
Georgina is the Digital Trends space writer, covering human space exploration, planetary science, and cosmology. She…
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