WASP-121b, also known as Tylos, is a giant, ultra-hot, gaseous planet located 858 light years from Earth. It’s hot because it sits so close to its sister star. In fact, it takes just over a day, or 30 hours, for the giant to orbit its star.
WASP is an exoplanet, or extrasolar planet, meaning that it’s found outside of our Solar System. And while we’ve known about it since 2016, the James Webb Space Telescope (JWST), — which launched four years ago — has helped us to gain a number of new insights about this gassy giant.
How Hot is WASP-121B?
“It’s so hot that basically any element, including things like iron and silicates, which are essentially rocks, will be vaporized and in the gas phase,” says Thomas Evans-Soma, an astronomer with the University of Newcastle in Australia. He recently led a study published in Nature Astronomy documenting the finding.
WASP is what’s called a “hot Jupiter,” or a category of exoplanets that are extremely hot. These are gas planets that are also huge and often brighter and easier to detect than some of the other exoplanets. WASP is also about 1.8 times the radius of Jupiter.
It orbits very close to a star that’s hotter than the sun. This is true of all hot Jupiters, which orbit their stars much closer than Mercury, the closest planet to the sun. And like WASP, most hot Jupiters orbit their host star quickly because of their location.
“If it was any closer to the star, then the gravitational tidal forces would be so great that it would be physically torn apart,” says Evans-Soma.
Read More: Exoplanet Winds Expose a World Out of Science Fiction
A Closer Look with JWST
While astronomers have observed the planet quite a bit with the Hubble Space Telescope, the new, much more powerful JWST has given scientists a closer look at its makeup.
“We were able to observe it at longer wavelengths than we had been able to before,” says Evans-Soma.
This means that they were able to observe WASP completing a full orbit around its host star, as well as noting the thermal emissions from the planet. In all, astronomers observed the planet for around 40 hours. The JWST is “ultra stable,” which means that it allows researchers to see that variations come from the planet and aren’t just the product of a shaky telescope.
And perhaps most importantly, JWST allowed researchers to detect new molecules in the planet that haven’t been detected before, like methane, carbon monoxide, and silicon monoxide.
The methane, in particular, was surprising because it had been commonly thought to be found on cooler planets like Uranus and Neptune. It was also found to be a carbon-rich planet.
What This Tells Us About the WASP’s Formation
The makeup of the gases suggests that WASP had to have formed far away and then traveled a great distance to be close to the star that it now orbits.
WASP came together as a result of little pebbles of gas, and then, in the heat, vaporized and eventually formed the planet. Because it has a carbon-rich environment, it likely formed in an area where methane-rich pebbles vaporized and released ample carbon into the atmosphere. Researchers were able to infer where the planet formed based on its composition, says Evans-Soma.
In the end, this study helps us to paint a picture of hot Jupiter formations in a way that we haven’t been able to before.
“It helps us to explain these hot [Jupiter] planets, which have been a mystery because we didn’t expect to find them so close to their host stars,” says Evans-Soma.
Read More: James Webb Space Telescope Captures Smallest Exoplanet Ever Seen in Historic First
Article Sources
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Sara Novak is a science journalist based in South Carolina. In addition to writing for Discover, her work appears in Scientific American, Popular Science, New Scientist, Sierra Magazine, Astronomy Magazine, and many more. She graduated with a bachelor’s degree in Journalism from the Grady School of Journalism at the University of Georgia. She’s also a candidate for a master’s degree in science writing from Johns Hopkins University (expected graduation 2023).
