For the first time, NASA scientists have strong evidence of a polar cyclone on Uranus. By examining the radio waves emitted by the ice giant, they discovered a phenomenon at the north pole of the planet.
The findings confirm a broad truth about all planets with substantial atmospheres in our solar system: Whether planets are composed mostly of rock or gas, their atmospheres show signs of a swirling vortex at the poles.
Scientists have long known that the south pole of Uranus has a swirling feature. Imaging of methane cloud tops by NASA’s Voyager 2 probe showed that the wind in the polar center rotates faster than over the rest of the pole. Voyager’s infrared measurements did not observe any temperature changes, but new findings published in Geophysical Research Letters did.
Using the Very Large Array antennas in New Mexico, they peered beneath the ice giant’s clouds and found that the circulating air at the North Pole appeared to be warmer and drier — signs of a powerful cyclone. Observations collected in 2015, 2021 and 2022 went deeper into Uranus’ atmosphere than ever before.
“These observations will tell us much more about the story of Uranus.” It’s a much more dynamic world than you might think,” said lead author Alex Akins of NASA’s Jet Propulsion Laboratory in Southern California. “It’s not just an ordinary blue ball of gas. There’s a lot going on under the hood.”
Uranus is showing off more these days thanks to the planet’s position in orbit. It’s a long way around the solar system for this outer planet, taking 84 years to complete a full circle, and the poles have not been facing Earth for the past few decades. Since about 2015, scientists have had a better view and could look deeper into the polar atmosphere.
Ingredients for Cyclone
Compact in shape with warm, dry air at its core, the cyclone on Uranus is very similar to those observed by NASA’s Cassini probe on Saturn. Thanks to the new findings, cyclones (which rotate in the same direction as their planet) or anticyclones (which rotate in the opposite direction) have now been identified at the poles on every planet in our solar system except Mercury, which has no substantial atmosphere.
But unlike hurricanes on Earth, cyclones on Uranus and Saturn do not form over water (neither planet is known to have liquid water) and do not drift; they are locked at the poles. Scientists will be watching closely how this newly discovered Uranian cyclone develops in the coming years.
“Is the warm core we observed the same high-velocity circulation seen by Voyager?” Akins asked. “Or are there stacked cyclones in the atmosphere of Uranus? The fact that we’re still finding out such simple things about how Uranus’ atmosphere works makes me really excited to learn more about this mysterious planet.”
The National Academies Decadal Survey of Planetary Sciences and Astrobiology in 2023 prioritized exploration of Uranus. In preparation for such a mission, planetary scientists are focusing on increasing their knowledge of the mysterious ice giant’s system.
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