A “hot Jupiter” exoplanet with a surface temperature hot enough to vaporize iron has been called by astronomers “one of the most extreme planets in the universe.”
Using data from the European Space Agency’s CHEOPS space telescope, astronomers at the University of Bern have studied the orbit, size and temperature of WASP-189b.
The planet, 322 light years from Earth, was first discovered orbiting its bright guest star HD 133112 by the Wide Angle Search for Planets (WASP) project in 2018.
CHEOPS was launched eight months ago by ESA to characterize known exoplanets and WASP-189b is the first planet to be explored 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.
This is an artist’s impression of WASP-189b orbiting its extremely hot “blue” star. The planet orbits the star every three days and has a permanent day and night side
This is an earlier artist impression of HD133112 and WASP-189b shared by NASA before the full extent of the ultra-hot surface was known
The star, named HD 133112, is the hottest star known to have a planetary system, according to Swiss astronomers behind the CHEOPS discovery.
Monika Lendl, lead author of the study from the University of Geneva, said WASP-189b was particularly interesting because it is a gas giant orbiting Earth close by.
It orbits 20 times closer to its star than Earth is to the Sun and is “very exotic” because it has a permanent day side that is always exposed to the light of its “very bright” host star.
The climate is completely different from that of the gas giants Jupiter and Saturn in our solar system, which have different sides facing the sun during their rotation.
Based on the observations with CHEOPS, we estimate the temperature of WASP-189b at 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 known to date, ”says Lendl.
The planet itself is too close to the host star for direct detection methods – so other techniques were needed to study it in more detail, the team explained.
Because the planet is so close to its host star, the day side is so bright that the team was able to measure the ‘missing light’ as it passes behind the star – a so-called occultation.
“We have observed several such coatings of WASP-189b with CHEOPS,” says Lendl.
It seems the planet doesn’t reflect much starlight. Instead, most of the starlight is absorbed by the planet, causing it to heat up and shine. ‘
The researchers think the planet is not very reflective because no clouds are present on the day side.
The system with WASP-189b is “very exotic” according to astronomers. The star is very hot – 3,600 F hotter than the sun – and the planet orbits the star every three days
“This is not surprising, as theoretical models tell us that clouds cannot form at such high temperatures,” said Willy Benz, co-author of the study at the University of Bern.
‘We also found that the gas giant’s transit for its star is asymmetrical. This happens when the star has brighter and darker zones on its surface. ‘
CHEOPS: A MISSION TO CHARACTER FAMOUS EXOPLANETS
CHEOPS is the shortened name for ESA’s signature ExOPlanet Satellite mission.
It is the first mission to study bright nearby stars already known to harbor exoplanets.
It will make very accurate observations of the size of the planet as it passes in front of its host star.
It will focus on planets in the size range from super-Earth to Neptune, with its data to infer the bulk density of the planets.
Cheops is the first small or S-class mission in ESA’s science program.
It is a partnership between ESA and Switzerland, with a dedicated consortium led by the University of Bern, and with significant contributions from 10 other ESA member states.
The first planet studied by CHEOPS was WASP-189b – an ultra-hot Jupiter planet that orbits its star every three days.
“Thanks to CHEOPS data, we can conclude that the star itself is spinning so fast that its shape is no longer spherical; but elliptical. The star is pulled out on its equator. Benz continues.
The star that WASP-189b orbits is very different from our Sun – it is significantly larger and more than 3,600 degrees Fahrenheit hotter.
Because it is so hot, the star appears blue and not yellowish white like the sun.
Willy Benz said, “Only a handful of planets are known to orbit such hot stars, and this system is by far the brightest.”
“The star itself is interesting – it’s not perfectly round, but it’s bigger and cooler at the equator than at the poles, making the star’s poles appear brighter,” says Lendl.
‘It spins so fast it is pulled out at its equator! Adding to this asymmetry is the fact that the path of WASP-189 b is sloped; it does not travel around the equator, but passes close to the poles of the star. ‘
This tilted orbit adds to the existing mystery of how hot Jupiters are formed – for a planet to have such an inclined orbit, it must have formed further out and pushed inward towards the star, the astronomers explained from.
This is believed to happen when multiple planets within a system compete for their position, or when an outside influence – say another star – disrupts the system and pushes gas giants towards their star and in very short orbits that are highly tilted.
“Because we measured such a slope with CHEOPS, it suggests that WASP-189 b has undergone such interactions in the past,” adds Lendl.
As a result, it sets a benchmark for further studies, the team explained – saying they expect further spectacular findings on exoplanets from CHEOPS.
The CHEOPS mission was launched in 2019 as a ‘follow-up tool’ to study known exoplanets in more detail and to characterize their orbits and temperature
CHEOPS uses two methods to study exoplanets: Transit – detecting the dimming of a star when a planet passes in front of it, and Occultation – when a planet passes behind a star and the light reflected from the planet is obscured
“This first result from Cheops is extremely exciting: it is an early final proof that the mission is living up to its promise in terms of precision and performance,” says Kate Isaak, Cheops project scientist at ESA.
Thousands of exoplanets have been discovered since 1995, and many more are expected to be found in the years to come – from space and ground missions.
“Cheops has a unique ‘follow-up’ role to play in studying such exoplanets,” explains Isaak, adding that it will look for transits of planets discovered on the ground and measure their dimensions more accurately.
“By following exoplanets in their orbits with Cheops, we can characterize a first step in their atmospheres and determine the presence and properties of clouds present,” added Isaac.
The research is published in the journal of Astronomy and Astrophysics.
Scientists are studying the atmosphere of distant exoplanets with the help of enormous space satellites such as Hubble
Distant stars and their orbiting planets often have conditions unlike anything we see in our atmosphere.
To understand this new world and what it is made of, scientists need to be able to detect what their atmosphere consists of.
They often do this by using a telescope similar to Nasa’s Hubble telescope.
These massive satellites scan the sky and target exoplanets that Nasa believes may be of interest.
Here the sensors on board perform various forms of analysis.
One of the most important and useful is absorption spectroscopy.
This form of analysis measures the light coming from a planet’s atmosphere.
Each gas absorbs light of a slightly different wavelength, and when this happens, a black line appears on a full spectrum.
These lines correspond to a very specific molecule, indicating that it is present on the planet.
They are often referred to as Fraunhofer lines, after the German astronomer and physicist who first discovered them in 1814.
By combining all of the different wavelengths of light, scientists can determine all of the chemicals that make up a planet’s atmosphere.
The key is what is missing provides the clues to find out what is there.
It is vital that this is done by space telescopes, as the Earth’s atmosphere then interferes.
Absorption by chemicals in our atmosphere would skew the sample, so it is important to study the light before it has had a chance to reach Earth.
This is often used to search for helium, sodium, and even oxygen in alien atmospheres.
This diagram shows how light passing from a star through an exoplanet’s atmosphere produces Fraunhofer lines that indicate the presence of important compounds such as sodium or helium.