Last December, the the European Space Agency’s (ESA) CHEOPS space telescope was carried into orbit 435 miles above Earth’s atmosphere with a mission to hunt for planets outside our Solar System (exoplanets.) It’s recently done precisely that—spotting an extreme world called WASP-198.
Imagine if you inflated Jupiter one and a half times its size and moved it between Mercury and the sun. Also imagine that said sun was blue because it’s 2,000 degrees hotter than our sun, and that our giant Jupiter—which contains vaporized iron in its atmosphere—traveled around it in a year equaling just three days. That would give you an idea of WASP-198. (It would also give us one heck of a star to see at night!)
“(It has) a permanent day side, which is always exposed to the light of the star, and, accordingly, a permanent night side,” said lead author Monika Lendl from the University of Geneva. “Based on the observations using CHEOPS, we estimate the temperature of WASP-189b to be 3,200 degrees Celsius (5792°F). 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.”
The fact that we know so much about this extreme planet located 322 light-years away is a testament to the success of the CHEOPS mission. As with other exoplanet observations, the CHEOPS data was obtained by noting how WASP-198 changes its sun’s light as it passes in front of it. But, because the planet is so large, hot, and close to its sun, the astronomers were also able to make observations about it when it was behind its sun.
“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,” said Lendl. “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 up and making it shine.”
CHEOPS also revealed another strange aspect of WASP-189b: it’s not even round.
“We also found that the transit of the gas giant in front of its star is asymmetrical,” said Willy Benz, professor of astrophysics at the University of Bern and head of the CHEOPS consortium. “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.”