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June 6, 2017

Newfound exoplanet is hotter than most stars

A newly-discovered planet is undergoing such extreme irradiation from its sun that it is hotter than most stars and has a giant glowing gas tail similar to those that form on comets, according to a new study published online Monday in the journal Nature.

The research, which was also presented at the 2017 spring meeting of American Astronomical Society (AAS)  in Texas, was led by astronomers at Vanderbilt and Ohio State universities and resulted in the discovery of the new world around a massive star located 650 light years away.

The planet is believed to be orbit a star identified as KELT-9 in the constellation Cygnus, and is purportedly a Jupiter-like planet that only takes 1.5 days to complete one trip around its sun, the study authors explained in a statement.

As a result, its day-side temperature exceeds 7,800 degrees Fahrenheit (4,600 Kelvin), making it just 2,000 degrees Fahrenheit (1,200 Kelvin) cooler than our sun and hotter than most other stars. Furthermore, the researchers believe that the intense radiation it is experiencing could be causing it to literally evaporate away, producing the aforementioned comet-like tail.

“It’s a planet by any of the typical definitions based on mass,” OSU astronomy professor Scott Gaudi, co-lead author of the study, explained “but its atmosphere is almost certainly unlike any other planet we’ve ever seen just because of the temperature of its day side.”

Chances of finding life on the new planet are ‘not...good’

Despite being nearly three times as massive as Jupiter, the new planet (KELT-9b) is only half as dense as the gas giant, as the radiation from its host star has caused its atmosphere to expand, the authors said. It is also tidally locked to its sun, meaning that its day side is constantly exposed to stellar radiation and its surface temperature is too hot for water and CO2 molecules to form.

KELT-9, the star around which this new planet orbits, is more than twice as large and nearly twice as hot as our sun, explained co-lead author and Vanderbilt physics and astronomy professor Keivan Stassun. As a result, the star “radiates so much ultraviolet radiation that it may completely evaporate the planet. Or, if gas giant planets like KELT-9b possess solid rocky cores as some theories suggest, the planet may be boiled down to a barren rock, like Mercury.”

Another possibility is that the planet will be swallowed up by KELT-9, should the star begin to expand to become a red giant – something that Stassun believes could happen “in about a billion years.” Either way, he added, “the long-term prospects for life... are not looking good.”

KELT-9b has an extremely short orbital period, a near-polar orbit and travels around a star that is oblate, not spherical, co-author Karen Collins, a post-doctoral fellow at Vanderbilt, noted. Based on her team’s calculations, the planet’s orbital precession will carry it out of view in around 150 years, and it will not reappear for another 3,500 years, she added, meaning that they were “pretty lucky to catch the planet while its orbit transits the face of the star.”

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Image credit: NASA JPL