Doomed exoplanet discovered with surface hotter than most stars

6 Jun 2017

Illustration of KELT-9b beside its neighbouring star. Image: NASA/JPL-Caltech

While planets in our own solar system, such as Venus, are considered hostile to life, spare a thought for the newly discovered exoplanet hotter than most stars.

The number of exoplanets being discovered in the known universe is increasing rapidly as our technology improves, and more details of these weird and fascinating worlds are being revealed.

The latest find, located 650 light years from Earth in the constellation Cygnus, was discovered by a team from Ohio State and Vanderbilt universities. The discovery revealed a planet so hot that it rivals most stars in temperature.

Future Human

The Jupiter-sized planet was found orbiting a massive star, KELT-9, and has a sweltering peak day temperature of 4,300 degrees Celsius, making it just 900 degrees Celsius cooler than our own sun.

In fact, the planet – KELT-9b – is essentially being cooked by intense ultraviolet radiation from its neighbouring star to such an extent that it is being evaporated, leaving a gas tail in its wake.

Other strange things discovered about this exoplanet include the fact that, despite it being a gas giant nearly three times as large as Jupiter, the extreme radiation has made it half as dense.

This has resulted in its atmosphere puffing up to the size it is, much like a balloon.

“It’s a planet by any of the typical definitions based on mass, but its atmosphere is almost certainly unlike any other planet we’ve ever seen, just because of the temperature of its day side,” said Scott Gaudi, one of the lead authors of the study.


KELT-9b orbiting its parent star. GIF: NASA/JPL-Caltech

A doomed planet

To put the fate of the exoplanet in perspective, the star KELT-9 is approximately twice as large as our own sun, but is also twice as hot.

The exoplanet draws possible comparisons with our solar system, as the intense radiation could one day boil down the planet to reveal a solid, rocky core, much like what we see with Mercury today. But the star will likely expand within a billion years and engulf KELT-9b anyway.

For the astronomers who discovered it in 2014, the find was described as “pretty lucky” by study co-author Karen Collins.

“Because of its extremely short period, near-polar orbit and the fact that its host star is oblate, rather than spherical, we calculate that orbital precession will carry the planet out of view in about 150 years, and it won’t reappear for roughly three and a half millennia,” she said.

Colm Gorey was a senior journalist with Silicon Republic