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Astronomers discovered a Jupiter-like planet, and it’s hotter than most stars

Astronomers just discovered a sizzling hot planet with a temperature higher than most stars. The  KELT-9b has a daytime temperature that reaches 7,800 degrees Fahrenheit.

Astronomers discovered the hottest planet in the known Universe. The KELT-9b planet was found using one of the two telescopes called KELT, or Kilodegree Extremely Little Telescope.

In late May and early June 2016, astronomers using the KELT-North telescope at Winer Observatory in Arizona noticed a tiny drop in the star’s brightness, only about half of one percent, which indicated that a planet may have passed in front of the star. The brightness dipped once every 1.5 days, which means the planet completes a “yearly” circuit around its star every 1.5 days.


Called KELT-9b, the Jupiter-like planet has a daytime temperature reaching 7,800 degrees Fahrenheit, making it hotter than most stars. According to NASA, the temperatures are probably unraveling the gas giant through evaporation.

“This is the hottest gas giant planet that has ever been discovered,” said Scott Gaudi, astronomy professor at The Ohio State University in Columbus, who led a study on the topic. He worked on this study while on sabbatical at NASA’s Jet Propulsion Laboratory, Pasadena, California. The unusual planet is described in the journal Nature and at a presentation at the American Astronomical Society summer meeting this week in Austin, Texas.

KELT-9b is actually almost three times more massive than Jupiter but only half as dense. And according to scientists, the extreme radiation from its host star has caused the planet’s atmosphere to puff up like a balloon.

Another interesting feature of the hellish planet is that it is tidally locked to its star, just as the moon is to Earth. This means that one side of the planet is always facing its star while the other side is forever covered in darkness.

Due to the increased ultraviolet radiation, molecules such as water, carbon dioxide and methane can’t form on the day side. Constantly blasted with high levels of ultraviolet radiation, the planet may even be shedding a tail of evaporated planetary material, just like a comet. In time, it could completely evaporate the entire planet, scientists surmise.

“KELT-9 radiates so much ultraviolet radiation that it may completely evaporate the planet,” said Keivan Stassun, a professor of physics and astronomy at Vanderbilt University, Nashville, Tennessee, who directed the study with Gaudi.

Scientists say that the properties of the nightside are still mysterious with molecules being able to form there only temporarily.


“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,” Gaudi said.

The KELT-9 star is only 300 million years old, which is young in star time. It is more than twice as large, and nearly twice as hot, as our own sun. And if the star grows, it could engulf the planet, before it evaporates.

“KELT-9 will swell to become a red giant star in a few hundred million years,” said Stassun. “The long-term prospects for life, or real estate for that matter, on KELT-9b are not looking good.”

The planet is also unusual in that it orbits perpendicular to the spin axis of the star. That would be analogous to the planet orbiting perpendicular to the plane of our solar system. One “year” on this planet is less than two days.

KELT-9b is a disappointment for those looking for new planets in the hope of finding extraterrestrial life. But for scientists, this remarkable world could provide important insights into how planetary systems form around massive stars.

“As has been highlighted by the recent discoveries from the MEarth collaboration, the planet around Proxima Centauri, and the astonishing system discovered around TRAPPIST-1, the astronomical community is clearly focused on finding Earthlike planets around small, cooler stars like our sun. They are easy targets and there’s a lot that can be learned about potentially habitable planets orbiting very low-mass stars in general. On the other hand, because KELT-9b’s host star is bigger and hotter than the sun, it complements those efforts and provides a kind of touchstone for understanding how planetary systems form around hot, massive stars,” Gaudi said.

The astronomers hope to take a closer look at KELT-9b with other telescopes, including NASA’s Spitzer and Hubble space telescopes, and eventually the James Webb Space Telescope, which is scheduled to launch in 2018.

Observations with Hubble would enable them to see if the planet really does have a cometary tail, and allow them to determine how much longer that planet will survive its current hellish condition.

“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. Such observations will allow us to get as complete a view of its atmosphere as is possible for a planet outside our solar system,” said Knicole Colon, paper co-author who was based at NASA Ames Research Center in California’s Silicon Valley during the time of this study.

Sylvia Jacob