Newly-discovered extremely hot planet may have comet-like tail

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Scientists have discovered an incredibly hot planet orbiting a blue star approximately 650 light-years from Earth.

The star's tumultuous radiation could be heating up and stripping away KELT-9b's atmospheric hydrogen and helium and flinging it into a tail like a comet's, Gaudi said. It's the first time astronomers have detected a planet near a star this hot, and it's different from anything they've seen before.

In this week's issue of the journal Nature and at a presentation at the American Astronomical Society spring meeting, an global research team led by astronomers at The Ohio State University and Vanderbilt University describes a planet with some very unusual features. The constant stream of radiation might eventually evaporate the planet's atmosphere, whittling the planet down to its core - or causing it to completely disappear. Its night side would be very dark red.

"It's a planet by any of the typical definitions based on mass, but its atmosphere is nearly certainly unlike any other planet we've ever seen just because of the temperature of its day side", said study author Scott Gaudi of Ohio State University in a statement.

Hannah Jang-Condell, a UW assistant professor of physics and astronomy, contributed data to a paper, titled "A Giant Planet Undergoing Extreme Ultraviolet Irradiation By its Hot Massive-Star Host", that appears in the June 5 issue (today) of Nature.

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"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", Stassun says.

The extreme ultraviolet radiation bombarding KELT-9b is causing its atmosphere to bleed into space, and it probably has a glowing gas tail reminiscent of a comet.

"Finding a wider range of these planets, especially ones that are amenable to further study like this one, is really important to trying to understand these types of worlds", says Gaudi.

"The astronomical community is clearly focused on finding Earthlike planets around small, cooler stars like our sun".

The planet is also unusual in that it orbits perpendicular to the spin axis of the star.

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Gaudi also said that the researchers relied on the help of a network of amateur astronomers to locate the planet. Deming also thinks the find has opened the door for a new approach to exoplanets.

To date, astronomers have documented thousands of exoplanets, but only six (including KELT-9b) have ever been found to orbit a so-called A-type star-a scorchingly hot brand of stellar object with temperatures between 7,300 and 10,000 Kelvin. Because of its close proximity, it's tidally locked to its star, with a distinct "day side" that is always facing the extreme heat source.

Subsequent observations confirmed the signal to be due to a planet, and revealed it to be what astronomers call a "hot Jupiter" - the kind of planet the KELT telescopes are created to spot.

KELT is short for "Kilodegree Extremely Little Telescope". Kelt-9b's orbit precesses, or wanders about, due to the fact that its star is somewhat egg-shaped, bulging out at the poles due to rotational forces. This results in the planet's day side being bathed with a glow that can split molecules.

It's a low-priced means of planet hunting, using mostly off-the-shelf technology: whereas a traditional astronomical telescope costs millions of dollars to build, the hardware for a KELT telescope runs less than $75,000. They used the Tillinghast Reflector Echelle Spectrograph at the Fred Lawrence Whipple Observatory in Arizona, which is operated by the Smithsonian Astrophysical Observatory.

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The astronomers aim to observe KELT-9b with other instruments, including NASA's Hubble and Spitzer space telescopes and the agency's $8.9 billion James Webb Space Telescope, which is scheduled to launch in late 2018.