KELT-9b is a planet hotter than most stars

Artist's concept of the star KELT-9 and the planet KELT-9b (Image NASA/JPL-Caltech)
Artist’s concept of the star KELT-9 and the planet KELT-9b (Image NASA/JPL-Caltech)

An article published in the journal “Nature” describes the study of the planet KELT-9b. This is an extreme case of hot Jupiter, a gas giant planet like Jupiter so close to its star to be considerably heated up. KELT-9b has an estimated surface temperature in the area exposed to its star that can exceed 4,600 Kelvin, so much that its atmosphere is likely to be dissipating in space and may have a tail similar to that of comets.

In 2014, the KELT-9b planet was discovered thanks to the observations of the KELT-North telescope, one of the two used by a collaboration run by the Ohio University, which aims to identify planets orbiting bright stars. Called Kilodegree Extremely Little Telescopes (KELT), they’re low budget instruments built to conduct bright star surveys covering a large area of ​​the sky.

The star KELT-9 is young in astronomical terms, with an estimated age of about three hundred million years. About twice as big and hot as the Sun, has still a relatively short life as it’s quickly consuming its hydrogen. Due to its characteristics, it’s withing the KELT collaboration’s parameters, with the consequent discovery of the planet called KELT-9b thanks to the fact that it passed periodically in front of its star.

After its discovery, the existence of the KELT-9b planet was confirmed by a number of other observatories. The astronomers quickly realized that it was a planet out of the ordinary: its year lasts only 36 hours so it must be very close to its star. The data indicate that this is a hot Jupiter but is an extreme case that according to Professor Scott Gaudi, the article’s lead author, challenges the typical definitions of planets.

The planet KELT-9b always shows the same face to its star, like the Moon with Earth, and that face has a higher temperature than most stars with its 4,600 Kelvin. In that area ultraviolet radiation is so intense that it prevents the formation of many otherwise common molecules. Its mass is about 2.8 times of Jupiter’s but its density is about half of Jupiter’s. The cause is its star, which heats it so much that it inflated it like a balloon.

The KELT-9b planet is interesting for its strange characteristics and thanks to its alignment with the Earth and its star is a good target for further observations. Space telescopes such as Hubble could help to understand if this exoplanet really has a tail formed by the gas that is getting lost. The astronomers would also like to estimate KELT-9b’s life expectancy: perhaps it will completely evaporate or will be destroyed by its star when it turns into a red giant in less than a billion years.

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