Around a star 880 light-years from Earth orbits one of the wildest, most extreme exoplanets we’ve found to date.
Its name is Tylos (WASP-121b), a world so scorchingly close to its sun that its atmosphere is thick with clouds of vaporized metal, and it rains liquid sapphires and rubies. Now, scientists have managed to reconstruct its tempestuous atmosphere in three dimensions, shattering a recently-set record for fastest known winds while revealing a climate unlike anything seen in our Solar System.
And it’s an absolute corker. Powerful jetstream currents blow clouds of iron and titanium faster than the exoplanet can rotate as vertical circulation patterns transport energy deep below.
“This planet’s atmosphere behaves in ways that challenge our understanding of how weather works – not just on Earth, but on all planets,” says astrophysicist Julia Victoria Seidel of the European Southern Observatory. “It feels like something out of science fiction.”
Of the nearly 6,000 confirmed exoplanets in the Milky Way, Tylos has one of the most-studied atmospheres out there. It’s what we call a hot Jupiter – a world comparable in size to our own gas giants, but so close to its star that its temperature is significantly hotter than some stars.
In fact, Tylos is one of the prototypical ultra-hot Jupiters. It’s around 1.74 times the radius and 1.16 times the mass of Jupiter; and it orbits its star so closely that its year lasts about 30 hours, leading to an equilibrium temperature of around 2,360 Kelvin (2,087 Celsius or 3,788 Fahrenheit). Between the heat and gravity, Tylos’ atmosphere is leaking out into space; the exoplanet is literally evaporating.
Hot Jupiters are fun to study for a few reasons. Any light that filters through the planet’s puffed-up atmosphere as they pass between us and their star can pick up clues on the elements and compounds likely to be floating around in there. It’s through this method that previous efforts have determined the different metals in Tylos’ atmosphere.
To study the planet in greater detail, Seidel and her colleagues brought to bear all four telescope units of the ESO’s Very Large Telescope, combining their might to determine not just what the atmosphere is made of, but the complex layers it comprises.
“What we found was surprising: a jet stream rotates material around the planet’s equator, while a separate flow at lower levels of the atmosphere moves gas from the hot side to the cooler side. This kind of climate has never been seen before on any planet,” Seidel says. “Even the strongest hurricanes in the Solar System seem calm in comparison.”
Because Tylos is so close to its host star, a yellow-white F-type star called Dilmun, it’s what we call tidally locked: its rotational period is the same as its orbital period. This means the same side is always facing the star, getting the full brunt of its scorching heat.
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The result of this is an extreme temperature gradient between the day side and the night side of its exoplanet, which stirs up powerful winds that can reach supersonic speeds. The researchers observed a jet stream that covers half the exoplanet that accelerates and churns up the atmosphere to high altitudes as it blows through the day side.
In the morning, its speed was measured at 13.7 kilometers (8.5 miles) per second. In the evening, that speed had almost doubled to 26.8 kilometers (16.7 miles) per second. That makes it the fastest atmospheric jet stream ever recorded.
A temperature difference of around 950 Kelvin between morning and evening on the exoplanet also shows that the jet stream is being heated as it flows.
At the bottommost atmospheric layer, winds blow clouds of iron at super-rotational speeds. That’s faster than the speed of the exoplanet’s rotation. Above that sits a layer of sodium, and above that a layer of hydrogen that’s leaking out into space.
And, underneath it all, for the first time, the researchers detected titanium in the exoplanet’s atmosphere. Previous censuses of its atmospheric contents found titanium lacking; now we know that it’s there, but buried deep under other layers. That discovery was published in a second, companion paper.
Hopefully, the team’s findings represent a bold surge forward for exoplanet research.
“It’s truly mind-blowing that we’re able to study details like the chemical makeup and weather patterns of a planet at such a vast distance,” says astrophysicist Bibiana Prinoth of Lund University in Sweden. “This experience makes me feel like we’re on the verge of uncovering incredible things we can only dream about now.”
The research has been published in Nature.
