Hottest Planet Ever Found Is Boiling Off Its Own Atmosphere


The hottest planet ever discovered by astronomers has temperatures so high, it is boiling off its own atmosphere and feeding it off to its host star.

Astronomers at the Max Planck Institute for Astronomy in Heidelberg, Germany say the future is not so bright for exoplanet KELT-9b.

As the superheated planet travels in orbit around a star that has temperatures nearly twice that of the sun, its puffy atmosphere made of hydrogen gas evaporates rapidly.

Exoplanet Just 650 Light-Years Away From Earth

In a paper published in Nature Astronomy, researchers Fei Yan and Thomas Henning say that the atmosphere of exoplanet KELT-9b is being heated to extremes by its host star KELT-9.

In 2017, a team of astronomers at the Ohio State University led by B. Scott Gaudi discovered exoplanet KELT-9b using the Kilodegree Extremely Little Telescope at the Winner Observatory near Sonoita, Arizona.

The goal of KELT is to find new exoplanets using the transit method. This is done by finding temporary dips in the brightness of a star, suggesting that an object has just moved in orbit in front of it.

Kelt-9b was found through this method toward the direction of the Cygnus constellation just 650 light-years from Earth, which is not far, according to astronomical standards.

KELT-9B Is A Superhot Jupiter

The planet, which is three times as heavy as Jupiter and almost two times as large, is in a very short orbit around its host star, which reaches temperatures of 17,500 degrees Fahrenheit. This is almost twice the temperature of the sun, which is around 9,900 degrees Fahrenheit.

The planet itself sits close to its host star, which is three times bigger than the sun. A trip around the star takes only 1.5 Earth days to complete. That is around 10 times smaller than Mercury's own orbit or a mere 3 percent of the diameter of the Earth's own orbit.

Planet KELT-9b's closeness to its star means it is tidally locked. The same side is always the dayside. On this side of the planet, temperatures can reach up to a searing 7,800 degrees Fahrenheit. This is hotter than most stars, according to experts.

"This planet reminds me of the mythical Icarus, who came close to the Sun and crashed," says Thomas Henning, co-author, and MPIA director. "Our planet will not crash, but it will certainly lose an essential part of itself, namely its atmosphere."

A Case Of Interplanetary Theft

Using the CARMENES spectrograph of the 3.5-meter telescope at the Calar Alto Observatory in Spain, the researchers have found that KELT-9 is not only blistering the exoplanet's atmosphere, it is also using its strong gravitational force to pull the planet's hydrogen towards itself.

The atmosphere is surprisingly large. It has, in fact, reached up to more than half the radius of the planet itself. Computer models simulating how the super-heated star siphons off hydrogen from the planet show the atmosphere is close to reaching its maximum size.

At this rate, the researchers say the planet is losing more than 100,000 tons of hydrogen per second. If the leeching off of hydrogen continues, experts believe the planet will lose its entire atmosphere and will be stripped down to its naked, rocky core.

In two Earth centuries, KELT-9 will have eaten up so much of the planet's atmosphere that it will grow to a point where it touches the planet's surface. All in all, the prospects are not good for the hottest exoplanet ever known to man.

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