Planet circles it’s sun in less than 3 days.
Using data from the European Space Agency CHEOPS space telescope, astronomers from the University of Bern studied the orbit, size and temperature of WASP-189b.
The planet, 322 light years from Earth, was first discovered orbiting its bright host star HD 133112 by the Wide Angle Search for Planets (WASP) project in 2018.
CHEOPS was launched by ESA eight months ago to characterise known exoplanets and WASP-189b is the first planet examined by the orbiting spaceship.
The gas giant planet is one and a half times the size of Jupiter and has a surface temperature of 5,792 degrees Fahrenheit – it takes just three days to orbit its star.
The star, named HD 133112, is the hottest star known to have a planetary system, according to the Swiss astronomers behind the CHEOPS discovery.
Monika Lendl, lead author of the study from the University of Geneva said WASP-189b was particularly interesting as it is a close orbiting gas giant.
It orbits its star 20 times closer than the Earth orbits the Sun and is ‘very exotic’ as it has a permanent day side always exposed to the light of its ‘very bright’ host star.
Its climate is completely different from that of the gas giants Jupiter and Saturn in our solar system which have different sides facing the Sun as they rotate.
‘Based on the observations using CHEOPS, we estimate the temperature of WASP-189b to be 3,200 degrees Celsius [5792 F].
In comparison, Jupiter has an average temperature of -234 degrees Fahrenheit.
‘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,’ says Lendl.
The planet itself is too close to the host star for any direct detection methods – so other techniques were needed to study it in more detail, the team explained.
As the planet is so close to its host star the dayside is so bright the team were able to measure the ‘missing light’ as it passes behind the star – called an occultation.
‘We observed several such occultations of WASP-189b with CHEOPS,’ Lendl says.
‘It appears that the planet does not reflect a lot of starlight. Instead, most of the starlight gets absorbed by the planet, heating it up and making it shine.’
The researchers 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,’ said Willy Benz, study co-author from the University of Bern.
‘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.’
It is a partnership between ESA and Switzerland, with a dedicated Consortium led by the University of Bern, and with important contributions from 10 other ESA Member States.
The first planet studied by CHEOPS was WASP-189b – an ultra hot Jupiter planet orbiting its star every three days.
‘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.’ continues Benz.
The star around which WASP-189b orbits is very different from our Sun – it is considerably larger and more than 3,600 degrees Fahrenheit hotter.
Because it is so hot, the star appears blue and not yellow-white like the sun.
Willy Benz said: ‘Only a handful of planets are known to orbit such hot stars, and this system is the brightest by far.’
‘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,’ says Lendl.
‘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.’
This tilted orbit adds to the existing mystery of how hot Jupiters form – for a planet to have such an inclined orbit it must have formed further out and been pushed inwards towards the star, the astronomers explained.