Astronomers discovered the hottest known exoplanet, KELT-9b, which is a gas giant located 650 light-years from Earth.

Temperatures on KELT-9b can reach 4,300 degrees Celsius or 7,700 degrees Fahrenheit during the day. That temperature is about 1,300 degrees Celsius cooler than the surface of our sun.

Astronomers discovered the hottest known exoplanet, KELT-9. Image credit: ScienceNews
Astronomers discovered the hottest known exoplanet, KELT-9. Image credit: ScienceNews

Venus, the planet in our solar system where temperatures are usually the hottest, averages a high of around 460 degrees Celsius at ground level.

KELT-9b is the hottest exoplanet ever discovered

On Monday, Scott Gaudi, a professor of astronomy at Ohio State University, published the findings in the journal Nature. Gaudi and his co-authors believe that KELT-9b outstanding heat is the result of its unusually close relationship with its unusually hot star.

“KELT-9b is one of the strangest exoplanets I’ve ever seen,” said Gaudi, who has been looking for exoplanets for the past two decades, according to The Washington Post.

The data gathered from observations of the exoplanet were so odd that Gaudi and another scientist made a bet –involving a bottle of single-malt scotch- on whether KELT-9b was, in fact, a planet. Gaudi won the bet.

Drake Deming, an astronomer at the University of Maryland who was not involved in the study, said that KELT-9b is a hybrid between a star and a planet, although he noted that calling the exoplanet a star-planet hybrid was “somewhat of an oversimplification.” KELT-9b is as hot as a regular star, even warmer than most, but unlike a star, the planet does not possess a nuclear core that fuses hydrogen into helium.

KELT-9b is a hybrid between a star and a planet. Image credit: Equilibrioinformativo.
KELT-9b is a hybrid between a star and a planet. Image credit:

Astronomers found the planet three years ago, using instruments named the Kilodegree Extremely Little Telescopes, or KELT. They noticed that as the exoplanet moved in front of the star, the star’s brightness dimmed. These dips occurred every 36 hours, said the researchers. The astronomers realized that KELT-9b is so close to its sun that it completed a yearly orbit in 1.5 Earth days.

KELT-9b is so hot that molecules are scarce on the exoplanet

Researchers believe KELT-9b is a strange planet. In our solar system, all the planets orbit the sun’s equator, but KELT-9b orbits around the poles of its sun. The hot exoplanet is tidally locked too, which means KELT-9b does not appear to spin on its axis as it orbits the star, in the manner that the same face of the moon always faces Earth. The hottest temperatures are recorded in KELT-9b’s dayside atmosphere, while the half of the planet is facing its star.

It’s not the first time astronomers find extremely hot planets, as they had previously discovered “hot Jupiter” planets, called after the planet because of their extreme temperatures and gas giant nature. However, all of those planets fell about a thousand degrees Celsius short of KELT-9b.

According to Jonathan Fortney, a University of California at Santa Cruz professor, KELT-9b is at the extreme end of the population of known gassy, hot giants. Fortney creates computer models to determine what’s in an exoplanet atmosphere. He was asked to model KELT-9b’s atmosphere, but the professor declined the request. He told the researchers that he couldn’t possibly do that, as the planet is way too hot.

A planet’s atmosphere is usually made up of molecules, which in return are made up of atoms bound together. Molecular hydrogen gas is common on Jupiter, for example, as are water vapor and other gases. However, KELT-9b’s dayside is an exception, as the extreme temperatures break molecules into its constituent atoms.

“Almost all the elements are in atoms, not in molecules,” said Fortney, according to The Washington Post. “It’s essentially too hot for molecules to exist.”

Hottest exoplanet discovered may have a tail like a comet’s

Gaudi and his team believe that KELT-9b may have a tail, like a comet, as the massive star blasts away at the exoplanet; it could expose bare rock and leave behind something like Mercury. Deming stressed that this hypothesis was unproven. He noted that they don’t know enough to suggest that radiation is stripping KELT-9b’s atmosphere.

Researchers noted that every planet’s days are numbered, but it appears as if KELT-9b is particularly precarious. As the KELT-9b star keeps running out of hydrogen, it will swell and cool to three times its current size, according to Gaudi.

“It will actually eat the planet. And then what happens – who knows?” noted Gaudi, according to The Washington Post.

However, researchers believe they have a lot of time to study KELT-9b. Gaudi said that he expects to study “everything” about the exoplanet’s system. Astronomers are lobbying to use other instruments to look at the exoplanet, such as the Hubble telescope, to discover whether it has a tail like a comet or not. If they succeed in pointing the Hubble telescope at the hot exoplanet, they expect to discern more precisely what makes up KELT-9b’s atmosphere.

Source: The Washington Post