Scientists identify polar cyclone on mysterious Uranus – 05/26/2023 – Science

It is a world shrouded in mystery. Seventh planet from the Sun, Uranus was seen up close only once nearly 40 years ago by a NASA probe that passed by and still carefully guards its secrets.

But new observations from a telescope based in New Mexico are offering a more complete understanding of its atmosphere, including the detection of a polar cyclone whose center measures a quarter the diameter of Earth, rotating close to its north pole.

Scientists were able to look deeper than ever into the atmosphere of Uranus – a planet classified as an ice giant, as well as its planetary neighbor Neptune. The discoveries painted a picture of a more dynamic planet than previously known.

“Although the overall composition of its atmosphere and interior is similar to that of Neptune — as far as we know — Uranus has some pretty unique characteristics,” said planetary scientist Alex Akins of NASA’s Jet Propulsion Laboratory in California, lead author. of research published in the journal Geophysical Research Letters.

“It rotates on its side. And yet its magnetic field is still misaligned with the axis of rotation. Atmospheric circulation and internal heat release appear weaker than Neptune’s, but there are still a number of dynamic features and storms that have been observed,” added Acres.

Blue-green in color due to the methane contained in its atmosphere composed mainly of hydrogen and helium, Uranus is the third largest planet in our solar system. It has an approximate diameter of 50,700 km and is large enough to accommodate 63 Earths within it. Uranus orbits the sun at a distance of about 2.9 billion kilometers, nearly 20 times farther than Earth. One orbit of it lasts 84 years.

Its unusual tilt makes Uranus appear to orbit the sun like a rolling ball.

The researchers, using the Very Large Array telescope in New Mexico (southwestern United States) to see below the clouds at the top of the atmosphere, found circulating air at the north pole that was warmer and drier, evidence of a strong cyclone. They were able to estimate the size of the storm’s center, but not the diameter of the entire cyclone, although it could potentially be larger than Earth.

The research confirmed that polar cyclones are present on every body in our solar system with a substantial atmosphere — every planet except Mercury, and even Saturn’s moon Titan.

“Polar cyclones are regions of strong winds that move in a direction determined by the planet’s rotation — clockwise on Venus and Uranus and counterclockwise on others — with different air properties between the interior and exterior,” said Akins. .

“The way they form is different on each planet,” he added. “On Earth, their strength is modulated by season due to the amount of sunlight. We’re not yet sure how they form on Uranus. It’s different from other cyclones in that it usually lasts longer and probably forms from an equilibrium. different from atmospheric processes and therefore a more typical (long-lasting) feature of the atmosphere. It is different from hurricanes, which form, move and dissipate over relatively short timescales.”

Most of Uranus’s mass is a dense fluid of icy materials—water, methane, and ammonia. Uranus is surrounded by two sets of faint rings and orbited by 27 small moons. Its atmosphere is the coldest of any of the eight planets, including the outermost, Neptune.

Its only close encounter with a spacecraft occurred during the Voyager 2 flight in 1986.

“There are a lot of unknowns,” Akins said. “How did it become tilted on its side? Is its interior really ‘colder’ than the gas giants (Jupiter and Saturn)? Why do we see atmospheric banding features that don’t line up with measured wind speeds? Why is the pole so drier than the equator? Are its satellites (moons) ocean worlds?”

^{Translated by Luiz Roberto M. Gonçalves}