NASA’s observation confirms presence of polar cyclone on Uranus

“These observations tell us a lot more about the story of Uranus. 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,” said Alex Akins of NASA’s Jet Propulsion Laboratory in Southern California, and the lead author of this story, in an official statement. 

NASA’s Voyager 2 first spotted this unusual swirling feature on the polar region of Uranus. It imaged a methane cloud with signs of high-speed winds spinning at the polar center as compared to the surroundings. However, the infrared measurements taken by the spacecraft were not able to reveal temperature variations that could be indicative of the cyclone. 

And even for ground-based telescopes, it was difficult to determine the planet's atmospheric dynamics due to the unusual orbit of this outer planet of our solar system.

But in this study, scientists got the view of the planet better than ever due to its current position in its long orbit around the Sun. Since about 2015, the planet has offered a better view to the ground-based telescope, and thus, scientists were able to peer into the polar regions of Uranus. NASA highlights that it will take at least 84 years to complete a full lap. 

Scientists note that the cyclone on Uranus forms a compact shape, which is similar to those spotted on Saturn by the Cassini spacecraft. Like Saturn, Uranus also has warm, dry air at its core than surroundings. 

“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,” said Akins. 

With these latest findings, cyclones or anti-cyclones have now been spotted at the poles of every planet in our solar system — apart from Mercury as it virtually has no atmosphere.

The results have been published in the journal Geophysical Research Letters.

Study abstract:

We present observations of Uranus in northern spring with the Very Large Array from 0.7 to 5 cm. These observations reveal details in thermal emission from Uranus' north pole at 10s of bars, including a dark collar near 80°N and a bright spot at the polar center. The bright central spot resembles observations of polar emission on Saturn and Neptune at shallower pressures. We constrain the variations in temperature and NH3/H2S abundances which could explain these features. We find that the brightness temperature of the polar spot can be recreated through 5 K temperature gradients and/or 10× depletion of NH3 or H2S vapor between 10 and 20 bars, both consistent with the presence of a cyclonic polar vortex. The contrast of the polar spot may have increased since 2015, which would suggest seasonal evolution of Uranus' polar circulation at depth.