Imma Perfetto
Cosmos science journalist
Astronomers have peered into the atmosphere of an exoplanet some 900 light-years away and found powerful weather patterns that make the most severe storms in the Solar System seem like a calm breeze.
“It feels like something out of science fiction,” says Julia Victoria Seidel, a researcher at the European Southern Observatory (ESO) in Chile and lead author of a paper, published in Nature.
“This planet’s atmosphere behaves in ways that challenge our understanding of how weather works – not just on Earth, but on all planets.”
The researchers mapped the 3D structure of its atmosphere, revealing winds made of hydrogen, sodium, and iron, which course around the planet in separate layers.
The exoplanet, WASP-121b, is an ultra-hot Jupiter – a gas giant that orbits its star so every 30 hours. It is tidally locked with one side forever facing its star, while the other remains in perpetual nighttime.
“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,” says Seidel.
“This kind of climate has never been seen before on any planet.”
The deepest layer is composed of the iron winds, which blow away from WASP-121b’s day side.
Above this is the extremely fast-moving sodium jet stream, which accelerates as it moves from the planet’s morning side (the transition from night to day) to the evening side (the transition from day to night).
Finally, there is an upper layer of hydrogen wind blowing outwards.
“Even the strongest hurricanes in the Solar System seem calm in comparison,” says Seidel.
The winds on WASP-121b reach speeds of up to 19km/s. For comparison, the fastest winds in the Solar System, on the planet Neptune, are only about 600m/s.
The observations were made by the ESPRESSO instrument on ESO’s Very Large Telescope (VLT), which measures the specific wavelengths of light absorbed by the atoms in the planet’s atmosphere as it passes in front of its host star.
“The VLT enabled us to probe three different layers of the exoplanet’s atmosphere in one fell swoop,” says study co-author Leonardo A. dos Santos, an assistant astronomer at the Space Telescope Science Institute in the US.
“It’s the kind of observation that is very challenging to do with space telescopes, highlighting the importance of ground-based observations of exoplanets.”
The observations also revealed the presence of titanium just below the jet stream, which is described in companion study in Astronomy and Astrophysics.
“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 Bibiana Prinoth, a PhD student at Lund University, Sweden, and ESO, who led the companion study and is a co-author of the Nature paper.
