The north pole of Uranus has a stormy vortex and we've just seen it for the 1st time (photo)

Three views of Uranus showing its newly discovered bright polar cap, which looks white, green and blue in these processed images taken in microwave light. (Image credit: NASA/JPL-Caltech/VLA)

A vortex of relatively warm air has been detected swirling beneath Uranus' clouds, providing strong evidence for the existence of a cyclone anchored at the planet's north pole. 

The findings add fuel to the fire that Uranus is not as atmospherically inert as it initially seemed when NASA's Voyager 2 spacecraft flew past the "ice giant" in January 1986.

The discovery of a northern vortex on Uranus was made through the detection of thermal emission in the form of radio waves picked up by astronomers using the Very Large Array (VLA) of radio telescopes in New Mexico.

Related: Photos of Uranus, the tilted giant planet

Polar vortices seem to be a common trait of all planets with atmospheres, at least in our solar system – they have been previously observed on Venus, Earth, Mars, Jupiter, Saturn, Uranus (at its south pole) and Neptune. High-altitude atmospheric jet streams are thought to be responsible for the formation of these vortices, although the details differ on each planet.

When Voyager 2 encountered Uranus, it detected changes in wind speeds, which can reach 560 mph (900 kph), at the planet's south pole and which are consistent with the existence of a polar vortex there. However, Voyager 2 did not get a view of the planet's north pole to see if there was a vortex there, too. Compounding this lack of up-close data, observing either of Uranus' poles from Earth has been difficult until recently. This is because Uranus orbits the sun tipped over onto its side by 97.8 degrees. In essence, it is "rolling" around the sun, which meant that for a long time we could only see the planet's equatorial region from our point of view. 

Since 2015, however, Uranus has rolled around the sun enough for us to begin to get a clearer view of its north pole as the planet enters northern spring. In 2018 and 2022, the Hubble Space Telescope observed a bright, smoggy cap over Uranus' north pole — the first evidence for a polar cyclone.

Now, observations of Uranus by the VLA, in 2015, 2021 and 2022, have measured the atmospheric circulation and temperature change in this polar cap. The VLA detected a "dark collar" ringing the planet at 80 degrees latitude, mirroring a bright collar observed by Voyager 2 around its southern pole, which is understood to be a denser part of the atmosphere. Inside this dark collar, the VLA detected a bright spot, indicating temperatures several degrees warmer in the center of the vortex than outside it (where temperatures can drop to minus 370 degrees Fahrenheit (minus 224 degrees Celsius). A bright, warmer spot like this is a very typical characteristic of a cyclone.

Uranus' bright polar cap, imaged by the Hubble Space Telescope in 2022. (Image credit: NASA/ESA/STScI/A. Simon (NASA-GSFC)/M. H. Wong (UC Berkeley)/J. DePasquale (STScI))

"These observations tell us a lot more about the story of Uranus," Alex Atkins of NASA's Jet Propulsion Laboratory in Southern California, who led the observations, said in a statement. "It's a much more dynamic world than you might think."

Unlike Earth's cyclones, Uranus polar vortex is not formed of water vapor but of ices of methane, ammonia and hydrogen sulfide. Nor does the storm drift, instead remaining rooted to the pole. Little else is known about it at this time.

"Does the warm core we observed represent the same high-speed circulation seen by Voyager? Or are there stacked cyclones in Uranus' atmosphere?" wondered Atkins.

In the recent Planetary Science and Astrobiology Decadal Survey issued by the U.S. National Academies, Uranus was highlighted as a priority for a new space mission. To support this goal, planetary scientists are doubling their efforts to study Uranus to help inform the scientific goals of any future mission. 

Observing and better understanding Uranus' polar cyclones is a key scientific aim, and Atkins and his colleagues hope to continue studying the north polar vortex for many years to come to observe if and how it might change over time. Already, there are indications that the warm core has begun to brighten as northern spring has progressed.

The results of the VLA observations were published Tuesday (May 23) in the journal Geophysical Research Letters.

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Keith Cooper
Contributing writer

Keith Cooper is a freelance science journalist and editor in the United Kingdom, and has a degree in physics and astrophysics from the University of Manchester. He's the author of "The Contact Paradox: Challenging Our Assumptions in the Search for Extraterrestrial Intelligence" (Bloomsbury Sigma, 2020) and has written articles on astronomy, space, physics and astrobiology for a multitude of magazines and websites.

  • jpdemers
    With the planet on its side, how did anybody decide which pole was "North"?
    Reply
  • billslugg
    Looking down on the Solar System from above (North) it can be seen that the Sun and all the planets except Uranus rotate counter clockwise. All planets also revolve counter clockwise around the Sun. On Uranus we look for the pole that is rotating counter clockwise and we find that pole tilted 98° to the Solar System. This likely happened because of a collision with another large planet very long ago.
    Reply
  • Meteoric Marmot
    Venus also rotates "clockwise" (retrograde).

    I find it curious that we acknowledge that Venus rotates retrograde while we say "Uranus orbits the sun tipped over onto its side by 97.8 degrees."

    To me it makes more sense to say that Uranus rotates retrograde with an 82.2-degree axial tilt.

    Anyone have a good explanation for this or is it "Just because"?
    Reply
  • billslugg
    Yes, you are correct, Venus is also retrograde. And yes, Uranus is "retrograde with an 82.2° axial tilt" but Joe Sixpack would not understand that. He can deal with "tipped on its side" though.
    Reply
  • jpdemers
    There are two conflicting definitions. One applies a "right-hand rule": if the fingers of your right hand indicate the direction of rotation, your thumb points north. The other is the International Astronomers Union (IAU) convention: the hemisphere of a planet that is mostly above the "invariable plane" (basically, the ecliptic plane) is the "northern" hemisphere. ("Above", by yet another convention, is the side where Earth's northern hemisphere is found.) Saying that Uranus has a "97.8° tilt" puts the (right-hand rule) "north" pole on the southern side of the ecliptic, contravening the IAU convention. (Which apparently does apply to Venus.)
    Joe Sixpack couldn't care less, but you'd think astronomers would have come to an agreement.

    I see a reference to the "North pole of Europa" in another Space.com article, which makes me look forward to designating the poles of Uranus' moons. :oops:
    Reply
  • Classical Motion
    There is a right hand rule and a left hand rule. The right hand rule is for "positive" charge and the left hand rule is for "negative" charge. Electrical charge is not positive and negative, it is left handed and right handed.

    This handedness gives charge an asymmetric state. The right handed charge resides in a charged state, and the left handed charge resides in discharged state. Once in a while these states can be temporarily inverted........giving science the mystery of anti-matter.
    Reply
  • Atilla De Bum
    Meteoric Marmot said:
    Venus also rotates "clockwise" (retrograde).

    I find it curious that we acknowledge that Venus rotates retrograde while we say "Uranus orbits the sun tipped over onto its side by 97.8 degrees."

    To me it makes more sense to say that Uranus rotates retrograde with an 82.2-degree axial tilt.

    Anyone have a good explanation for this or is it "Just because"?
    Uranus must be a Captured planet, already rotating from its initial orbit around a sun that went supernova and kicked it loose.
    Reply
  • Atilla De Bum
    Sun spot activity has hit Uranus with a large CME, causing the effects we see now.
    Reply
  • Classical Motion
    How dense, would a CME be?............by the time it reached Uranus?
    Reply