Astronomers using the Karl G. Jansky Very Large Array in New Mexico have observed a bright, compact spot centered at Uranus’ north pole at several wavelengths. This feature likely indicates the presence of a polar cyclone and shows similarities to polar features observed on other giant planets in our Solar System.
Akins et al. used microwave observations to spot the first polar cyclone on Uranus, seen here as a light-colored dot to the right of center in each image of the planet. The images use wavelength bands K, Ka, and Q, from left. Image credit: NASA / JPL-Caltech / VLA.
Scientists have long known that Uranus’ south pole has a swirling feature.
NASA’s Voyager 2 imaging of methane cloud tops there showed winds at the polar center spinning faster than over the rest of the pole.
Voyager’s infrared measurements observed no temperature changes, but the new findings do.
Using huge radio antenna dishes of the Very Large Array in New Mexico, Dr. Alex Akins from NASA’s Jet Propulsion Laboratory and colleagues peered below the ice giant’s clouds, determining that the circulating air at the Uranian north pole seems to be warmer and drier.
Collected in 2015, 2021, and 2022, the observations went deeper into Uranus’ atmosphere than any before.
“These observations tell us a lot more about the story of Uranus,” Dr. Akins said.
“It’s a much more dynamic world than you might think.”
“It isn’t just a plain blue ball of gas. There’s a lot happening under the hood.”
Uranus is showing off more these days, thanks to the planet’s position in orbit.
It’s a long haul around the solar system for this outer planet, taking 84 years to complete a full lap, and for the last few decades the poles weren’t pointed toward Earth.
Since about 2015, astronomers have had a better view and have been able to look deeper into the polar atmosphere.
The cyclone on Uranus, compactly shaped with warm and dry air at its core, is much like those spotted by NASA’s Cassini at Saturn.
With the new findings, cyclones (which rotate in the same direction their planet rotates) or anti-cyclones (which rotate in the opposite direction) have now been identified at the poles on every planet in our solar system except for Mercury, which has no substantial atmosphere.
But unlike hurricanes on Earth, cyclones on Uranus and Saturn aren’t formed over water (neither planet is known to have liquid water), and they don’t drift; they’re locked at the poles.
The astronomers will be watching closely to see how this newly discovered Uranus cyclone evolves in the coming years.
“Does the warm core we observed represent the same high-speed circulation seen by Voyager?” Dr. Akins said.
“Or are there stacked cyclones in Uranus’ atmosphere? The fact that we’re still finding out such simple things about how Uranus’ atmosphere works really gets me excited to find out more about this mysterious planet.”
The findings appear today in the journal Geophysical Research Letters.
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Alex Akins et al. 2023. Evidence of a Polar Cyclone on Uranus From VLA Observations. Geophysical Research Letters 50 (10): e2023GL102872; doi: 10.1029/2023GL102872
