And not only the exoplanet – WASP-189b – is extreme; his mother star also turns out to be quite special.
The brand new planet hunter CHEOPS has now been in space for several months. CHEOPS’s job is to reveal more information about mysterious worlds already discovered. And the planet hunter certainly does not fall short in this. Because now, during its very first, real mission, CHEOPS has managed to unmask the secrets of a very special exoplanet.
Although scientists have long speculated about the existence of exoplanets, the first was not discovered until 1995. In the meantime, the counter has already reached at least 4000 exoplanets, mainly due to the great achievements of planet hunter Kepler. We now know that the universe is home to a very wide range of exoplanets, ranging from gaseous worlds larger than Jupiter to smaller, rocky planets. And now it’s up to CHEOPS to learn more about these mysterious worlds. The satellite will therefore not start looking for exoplanets itself, but will instead continue research into already discovered planets. The detection of an exoplanet is just the beginning. What Kepler – and other planet hunters like the recently launched TESS – are telling us is where the exoplanets are, how long it takes them to complete a circle around their star, and their approximate size. But it often ends there. Other specialized tools are needed to uncover the secrets of these exoplanets. What are they made of? Do they have an atmosphere? Are they livable? These are just some of the questions that astronomers hope to find answers to in the near future. And ESA’s CHEOPS, launched in December 2019, can help.–
CHEOPS has set its sights on – as it turns out – one of the most extreme exoplanets ever. The planet hunter was staring at the 2018 exoplanet WASP-189b orbiting the hot star HD 133112. And that resulted in some very interesting discoveries. For example, WASP 189b is much larger than expected with nearly 1.6 times the radius of Jupiter from our own solar system. Moreover, the planet is a real ‘ultra-hot Jupiter’. Hot Jupiters are, as the name suggests, giant gas planets that look a bit like Jupiter. However, they rotate much closer to their host star and are thus heated to extreme temperatures. The researchers think that WASP-189b is about 20 times closer to its star than Earth is to the sun. The planet orbits its parent star in just 2.7 days.
Extreme hitte
It means that the temperatures on the planet can get quite high. To determine how hot it could get, the researchers used CHEOPS to observe WASP-189b as it passed behind its host star. “Because the planet is so bright, there is actually a noticeable dip in light that we see coming out of the system when it disappears from view for a moment,” explains lead author Monika Lendl. “We used this to measure the brightness of the planet and keep its temperature down to a scorching 3,200 degrees Celsius.” This makes WASP-189 b one of the hottest and most extreme planets known to us. Moreover, the planet is completely different from the planets from our own familiar solar system. At the measured high temperatures, even metals such as iron melt and turn into gas. And that makes WASP-189b – unsurprisingly – clearly uninhabitable.
The discovered characteristics of the WASP-189b system. Image: ESA
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But not only WASP-189b is extreme. His mother star also turns out to be quite special. HD 133112 is larger and more than 2000 degrees hotter than our sun and also appears to glow blue. “Only a handful of planets are known to orbit such hot stars,” says Lendl. “And this system is by far the clearest. WASP-189b is also the brightest hot Jupiter we can observe when it is in front of or behind its star, making the whole system fascinating. ” In addition, the star is not perfectly round, but larger and cooler at the equator than at the poles. “This makes the poles of the star appear brighter,” says Monika. In addition, the star spins very quickly, which even pulls it out at its equator. “In addition, the WASP-189b trajectory has a ramp angle,” says Monika. “It does not move around the equator, but passes close to the poles of the star.”
Tilted track
The discovery of such a tilted orbit adds to the existing mystery of how hot Jupiters form. For a planet to have such an oblique orbit, it must have formed further out and then pushed inward. This is thought to happen when multiple planets within a system ‘compete’ for position. It can also arise when an external influence – for example another star – disrupts the system, pushing gas giants towards their star. As a result, they end up in very short, highly tilted orbits. “Because we’ve now measured such a tilt with CHEOPS, we believe WASP-189b has undergone such interactions in the past,” adds Monika.
Above expectations
Not only does the study reveal beautiful details about bizarre and distant exoplanets, it also reveals the unprecedented potential of CHEOPS. The planet hunter opened its eyes last January and then began routine scientific operations in April. First the satellite peered at a series of stars with known properties to determine how well CHEOPS is performing. And the planet hunter turned out to exceed all expectations. In recent months, CHEOPS has been working to expand our understanding of exoplanets and the nearby cosmos. “This first CHEOPS result is very exciting,” says Kate Isaak, Cheops project scientist at ESA. “It is early and definitive proof that the mission delivers on its promise of precision and performance.”
Over the next few years, Cheops will observe hundreds of known planets orbiting bright stars, building on what has been done here for WASP-189b. So we can count on many more interesting and special discoveries. “CHEOPS will not only deepen our understanding of exoplanets,” says Kate. “But also that of our own planet, our solar system and the wider cosmic environment.”
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