Scorching alien planet is most extreme world ever discovered

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A hellish alien Jupiter-like world that is hotter than most stars and glows like a comet has been discovered by an international team of astronomers.

The most extreme world ever discovered is so hot it’s likely that molecules break apart and atmosphere evaporates.

However, the young giant planet, dubbed KELT-9b, may already be heading towards a fiery death as it orbits so close to its “unevolved” host star that it is likely to be consumed as the young star ages.

The discovery by the team, which included amateur astronomers from Australia, opens up the possibility of furthering our understanding of how planetary systems evolve from birth to death.

The planet orbits a star called KELT-9, located 650 light-years away from Earth in the constellation of Cygnus, once every 36 hours, the team report today in the journal Nature.

Co-author Professor Scott Gaudi, at Ohio State University, said with a temperature of 10,200 degrees kelvin (9,926 degrees Celsius) KELT-9 is the hottest, most massive and most luminous star known.

By comparison our Sun’s temperature is about 5,800 degrees kelvin (5,526C), he added.

“The planet, KELT-9b, itself is about 4,600 degrees kelvin, which is about 1,200 degrees kelvin cooler than the Sun,” Professor Gaudi said.

One side of the planet continually faces its Sun so it is perpetually bombarded by radiation.

“The dayside of this planet is being heated up by the radiation from its star to a temperature that is hotter than the surface temperature of most stars we know about,” Professor Gaudi said.

“We don’t really know what the surface of this planet would be like [but] we think the dayside of the planet is so hot you can’t have any molecules there; no water vapour, no methane, no carbon dioxide.”

He said it was likely the heavy elements, sodium and potassium, were also present and along with hydrogen and helium the main components of the atmosphere.

Going out in a blaze of fire

However, the planet’s future was not looking bright, he said.

Intense heat from its host star was causing the planet to lose its atmosphere at the rate of between 10 billion and 10 trillion grams per second.

“The planet is evaporating and leaving behind a fair amount of hydrogen and helium in some sort of comet-like tail as it orbits the star,” Professor Gaudi said.

He said the most likely future for KELT-9b was that it would be swallowed in about 300 million years by its star as KELT-9 ran out of hydrogen and began to expand.

“When KELT-9 gets to be about three times the size it is it is now it will encroach on the orbit of the planet and swallow it … resulting in a transient flash of light and maybe in a giant star,” he said.

An alternative scenario would see the planet evaporated down to its core by the time KELT-9 ran out of hydrogen “and then the star will swallow the core whole and it will sink to the centre of the star”.

Citizen scientists help verify results

The initial discovery was made using the Kilodegree Extremely Little Telescope (KELT) North, a robotic telescope located in Arizona.

However, Professor Gaudi said the confirmation of transiting planets required extensive verification to ensure the signals were not false positives — systems that mimicked a transit signal but were not transiting exoplanets.

“The relatively low precision [of the signal] means we require a network of astronomers all over the world so they can follow up the signals to confirm the shape and size is what we would expect in a planet,” Professor Gaudi said.

The discovery included observations made by three Australian amateur astronomers Thiam-Guan Tran from Perth, Ivan Curtis in Adelaide and Chris Stockdale from Hazelwood in Victoria.

Professor Gaudi said KELT-9b would be studied for “decades to come”.

“It will give us important insights because we don’t have any analogues of these planets in our solar system and it can show us the properties of these planets and how these systems behave,” he said.

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