Hottest-Ever Alien Planet Discovered - KELT-9b is Hotter Than Most Stars

Imagine a planet like Jupiter zipping around its host star every day and a half, superheated to temperatures hotter than most stars and sporting a giant, glowing gas tail like a comet.

That is what an international research team led by astronomers at Ohio State and Vanderbilt universities think they have found orbiting a massive star they have labeled KELT-9, located 650 light years from Earth in the constellation Cygnus.

With a day-side temperature peaking at 4,600 Kelvin (more than 7,800 degrees Fahrenheit), the newly discovered exoplanet, designated KELT-9b, is hotter than most stars and only 1,200 Kelvin (about 2,000 degrees Fahrenheit) cooler than our own sun. In fact, the ultraviolet radiation from the star it orbits is so brutal that the planet may be literally evaporating away under the intense glare, producing a glowing gas tail.

The super-heated planet has other unusual features as well. For instance, it's a gas giant 2.8 times more massive than Jupiter but only half as dense, because the extreme radiation from its host star has caused its atmosphere to puff up like a balloon. Because it is tidally locked to its star—as the moon is to Earth—the day side of the planet is perpetually bombarded by stellar radiation and, as a result, it is so hot that molecules such as water, carbon dioxide and methane can't form there.

The discovery is described this week in a paper titled "A giant planet undergoing extreme-ultraviolet irradiation by its hot massive-star host" published by the journal Nature and in a presentation at the spring meeting of American Astronomical Society in Austin, Texas.

Phys.Org Read more at: https://phys.org/news/2017-06-extreme-exoplanet-astronomers-alien-world.html#jCp

nature.com https://www.nature.com/articles/nature22392

Clips, images credit: ESA, ESO, HUBBLE NASA