Exoplanet WASP-189b is one of the most extreme planets in the universe

CHEOPS keeps its promise.


Using data from CHEOPS, scientists have recently carried out a detailed study of the exoplanet WASP-189b. WASP-189b is an exoplanet that orbits around the star HD 133112, one of the hottest stars known to have a planetary system.

Located around 322 light-years away in constellation Libra (the weighing scales), WASP-189b is more than one and a half times as massive as Jupiter, the largest planet of the Solar system. The planet is especially interesting because it is a gas giant that orbits very close to its host star. It takes less than three days to circle its star, and it is 20 times closer to it than Earth is to the Sun.

Monika Lendl further explains that planetary objects like WASP-189b are very exotic: “They have a permanent dayside, which is always exposed to the light of the star, and, accordingly, a permanent night side. This means that its climate is completely different from that of thpiter and Saturn’s gas giants in our solar system. Based on the observations using CHEOPS, we estimate the temperature of WASP-189b to be 3,200 degrees Celsius. Planets like WASP-189b are called “ultra-hot Jupiters.” Iron melts at such a high temperature, and even becomes gaseous. This object is one of the most extreme planets we know so far.”

CHEOPS uses highly precise brightness measurements: When a planet passes in front of its star as seen from Earth, the star seems fainter for a short time. This phenomenon is called a transit.

Monika Lendl explains, “Because the exoplanet WASP-189b is so close to its star, its dayside is so bright that we can even measure the ‘missing’ light when the planet passes behind its star; this is called an occultation. We have observed several such occultations of WASP-189b with CHEOPS. It appears that the planet does not reflect a lot of starlight. Instead, most of the starlight gets absorbed by the planet, heating it and making it shine.”

Scientists believe that the planet is not very reflective because there are no clouds present on its dayside: This is not surprising, as theoretical models tell us that clouds cannot form at such high temperatures.

Willy Benz, professor of astrophysics at the University of Bern, said, “We also found that the transit of the gas giant in front of its star is asymmetrical. This happens when the star possesses brighter and darker zones on its surface. Thanks to CHEOPS data, we can conclude that the star itself rotates so quickly that its shape is no longer spherical; but ellipsoidal. The star is being pulled outwards at its equator.”

Monika Lendl says, “The star around which WASP-189b orbits is very different from the Sun. The star is considerably larger and more than two thousand degrees Celsius hotter than our Sun. Because it is so hot, the star appears blue and not yellow-white like the Sun. Only a handful of planets are known to orbit such hot stars, and this system is the brightest by far.” As a consequence, it forms a benchmark for further studies.”

In conclusion, Willy Benz explains“We are expecting further spectacular findings on exoplanets thanks to observations with CHEOPS.” 

The results have just been accepted for publication in the journal Astronomy & Astrophysics.


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