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Scientists find distant planet that’s so hot iron would evaporate there

Europe’s CHEOPS satellite, launched in December last year, has uncovered details about its first exoplanet: An extreme world that is one of the hottest planets ever studied, where even metals like iron would evaporate and turn into gas.

The planet, named WASP-189 b, is of a type called an ultra-hot Jupiter, because it is a gas giant like Jupiter and it is (you guessed it) ultra-hot.

The planet orbits 20 times closer to its star than Earth does to the sun, zipping around in a year which lasts just 2.7 days. Not only does it orbit extremely close to its star, but that star itself is also incredibly hot, being over 2,000 degrees Celsius hotter than the sun. In fact, the star is so hot that it would appear to glow blue.

It was the extreme brightness of the star which allows astronomers to spot the planet, as lead author Monika Lendl of the University of Geneva, Switzerland explained: “As the planet is so bright, there is actually a noticeable dip in the light we see coming from the system as it briefly slips out of view. We used this to measure the planet’s brightness and constrain its temperature to a scorching 3,200 degrees C.”

Artist impression of WASP-189
Artist impression of exoplanet WASP-189b orbiting its host star. The system was observed by ESA’s exoplanet mission Cheops to determine key characteristics. For example, the host star is larger and more than 2000 degrees hotter than our own Sun, and so appears to glow blue. ESA

The whole system is hot, bright, and unusual. “Only a handful of planets are known to exist around stars this hot, and this system is by far the brightest,” Lendl said. “WASP-189b is also the brightest hot Jupiter that we can observe as it passes in front of or behind its star, making the whole system really intriguing.”

As well as the hot planet, the star in this system has some interesting properties which grabbed the researchers’ attention. “We also saw that the star itself is interesting — it’s not perfectly round, but larger and cooler at its equator than at the poles, making the poles of the star appear brighter,” Lendl said. “It’s spinning around so fast that it’s being pulled outwards at its equator! Adding to this asymmetry is the fact that WASP-189 b’s orbit is inclined; it doesn’t travel around the equator, but passes close to the star’s poles.”

The information about the tilted orbit of the planet was of particular interest as it suggests that at some point in its history, it was influenced by other planets or another star, pushing it into its position closer to its star. This could help to unravel the mystery of how these extremely hot gas giants form.

The findings are published in the journal Astronomy & Astrophysics.

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