This scorching exoplanet is hotter than most stars

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Jun 8, 2017

Even with air conditioning, SPF and a frozen margarita, you probably wouldn’t want to take a vacation on KELT-9b.

Never mind it being more sweltering than your average star. The heat on the dayside of this tidally locked gas giant—the hottest gas giant ever discovered—is intense enough for its own star to vaporize it. An average temperature of 7,800 Fahrenheit would do that. It orbits even more extreme blue A-type star KELT-9, whose intense ultraviolet radiation has inflated the planet’s atmosphere and will probably obliterate KELT-9b into ghosts of steaming vapor if it doesn’t expand enough to devour its victim first.

Observed by one of the two KELT (Kilodegree Extremely Little Telescope) telescopes, this is one extreme exoplanet. Forget habitability. It is impossible for molecules of water, carbon dioxide and methane to form on the dayside, where the surface is being relentlessly bombarded with UV radiation. Whether or not anything could take hold on the nightside is unknown, but doubtful. Scientists even believe that there is a possibility that the nonstop UV blast may have even given this exoplanet a comet tail of evaporated material. KELT-9b makes the almost nonexistent atmosphere and solar wind-stripped surface of Mars sound like a tropical getaway.

"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," said Ohio State University astronomy professor Scott Gaudi, whose recent study at NASA’s Jet Propulsion Laboratory was published in the journal Nature.

KELT North, the telescope that observed KELT-9b.

KELT-9 isn’t a star in its final death throes of radiation, either. At only 300 million years old, it boasts twice the size and heat of the sun. It still has another few hundred million years before it enters the red giant phase. Meaning, prospects for its orbiting planet are grim. It’s going to live fast and die hard.

So why study the seventh circle of hell in space? Potentially habitable planets with cool host stars (think TRAPPIST-1) have been singled out as prime targets for further investigation. Even though we’re never going to see anything crawling around on KELT-9b, even under a microscope, studies of planets in the habitable zone could actually benefit from observations of such extreme environments. The enormous ball of fire KELT-9b is engaged in a deadly dance with beats the sun in size and scorch factor. This star it can illuminate how planetary systems emerge from around similar fiery orbs, even though that seems like a death wish.

Astronomers look forward to zeroing in on KELT-9b with other telescopes, especially NASA’s Spitzer and Hubble space telescopes and the upcoming James Webb telescope, which launches next year. They are most eager to use future observations for determining whether the planet has any chance of survival—and whether it really does have a cometary tail.

"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,” said study coauthor Knicole Colon, who was based at NASA’s Ames Research Center during the time of this 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." 

(via NASA)