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This Hell Planet Has Metal Clouds, Astronomers Say

A football-shaped hot Jupiter has a seriously hardcore climate.

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An artist's illustration of the hot Jupiter as a redd-ish orange world, with its host star at right.
An artist’s illustration of the hot Jupiter with a wacky weather pattern.
Illustration: Engine House VFX

New observations of the football-shaped exoplanet known as WASP-121b have revealed clues to its atmosphere and weather. Astronomers say it may have metal clouds made up of iron, corundum, and titanium.

WASP-121b orbits a star 850 light-years from Earth and is twice as large as our Jupiter. (It’s classified as a hot Jupiter, meaning its a gas giant that orbits relatively close to its star.) WASP-121b completes a revolution in just 30 hours—only slightly longer than an Earth day. It also has a bizarrely oblong shape, which is due to the intense gravitational forces the planet is subject to.


But the really surprising element of the latest findings are the details of the planet’s climate; how its temperatures plummet at night and change throughout the atmosphere. The team observed the hot Jupiter using the Hubble Space Telescope, and their study is published this week in Nature Astronomy.

“Hot Jupiters are famous for having very bright day sides, but the night side is a different beast,” said Tansu Daylan, an astrophysicist at MIT and a co-author of the paper, in an institute release. “WASP-121b’s night side is about 10 times fainter than its day side.”


The vastly different temperatures on either side of the planet make a dynamic environment for the various molecules floating around the atmosphere. In the daytime, water gets ripped apart by the nearly 5,000° Fahrenheit heat and blown to the night side of the planet by 11,000-mile-per-hour winds. “These winds are much faster than our jet stream, and can probably move clouds across the entire planet in about 20 hours,” Daylan said.

On the night side, the hydrogen and oxygen atoms recombine, only to whip around back to the dayside to get split again. It’s much more volatile than Earth’s water cycle of evaporating, condensing, and raining, even when our world is at its most violent.

What’s more, the planet’s night side is cold enough that it may foster clouds made of metal. Hot temperatures on the planet’s warm side may vaporize iron, corundum, and titanium, which may cause rains of heavy metal back on the cold side when the gaseous clouds whip around. Previously, another hot Jupiter—WASP 76b—showed signs of a similar phenomenon.

Following up on the recent Hubble observations, the team has reserved observation time on the newly launched Webb Space Telescope, which is set to begin its scientific work this summer. (Currently, Webb is still getting set up.) They want to map the planet’s carbon monoxide, which lead author Thomas Mikal-Evans, an astrophysicist at MIT, said could help the researchers understand how hot Jupiters form.


In millions of years, the tidal forces WASP121-b endures will tear the planet apart. Until then, the planet will continue its extraordinary dance of day and night.

More: Encouraging Webb Telescope Image Shows a Single Star in a Familiar Pattern