Jupiter’s gigantic super polar cyclones are here to stay
Scientists at the Weizmann Institute reveal how massive cyclones remain stable at both Jupiterpoles.
Until recently, before ">NasaThe Juno space probe entered orbit around the planet Jupiter, no one knew that powerful cyclones, approximately the size of Australia, were raging in its polar regions. Jupiter’s storms, unlike their terrestrial variety, do not disperse, barely change, and clearly not associated with flying roofs and wet weather reporters. In an article published recently in Geosciences of nature, researchers at the Weizmann Institute of Science are revealing the mysteries of Jupiter’s cyclones: what forces are at work to fix these gargantuan thunderstorms at their polar locations, and why their numbers and locations remain more or less constant over time.
“We can think of Jupiter as an ideal climate laboratory,” says Professor Yohai Kaspi of Weizmann’s Department of Earth and Planetary Sciences. The Earth is a complex and multivariable system: it has oceans and an atmosphere, continents, biology – and of course, human activity. Jupiter, on the other hand, the largest planet in our solar system, is made up of gas and therefore is a much easier system to study, a system for which we can make predictions and test hypotheses. The data necessary for these predictions and hypotheses are collected by Juno, a research probe launched by NASA in 2011 and which entered Jupiter’s orbit in mid-2016. Kaspi, NASA’s co-investigator on the Juno mission, witnessed one of his most exciting discoveries: cyclonic storms swirling around the poles of the planet.
“If we look at older images of Jupiter taken before 2016,” Kaspi says, “we see that the poles were generally represented as large gray areas because no one then knew what they actually looked like. The reason is that the solar system is organized on the same plane, which is very close to the plane of Jupiter’s equator. Therefore, past observations of the planet that have been made from Earth, or on previous space missions, could for the most part only capture the low latitudes of Jupiter. Thus, one of the notable innovations of the Juno mission is its polar orbit, which allowed researchers to observe in detail for the first time the tumultuous poles of Jupiter. This is exactly how the cyclones were displayed, surprisingly organized and resembling a round tray of cinnamon buns, along latitude 84 ° N and S. Additionally, data collected from Juno’s many orbits around Jupiter indicate that the number of cyclones remains fixed – eight are active around the north pole and five around the south. “This discovery was very surprising at the time,” Kaspi explains, “because we expected the poles to be more or less symmetrical.” In a previous study, Kaspi used the lack of symmetry of Jupiter’s gravitational field to determine the depth of the strong east-west wind belts characteristic of the planet’s atmosphere.
Kaspi: “The poles of Jupiter and the other gaseous planets are perhaps the last points in the solar system that still have to be explored”
On Earth, tropical cyclonic storms form in areas where the water temperature exceeds 26 degrees Celsius – usually in the center of the Atlantic and Pacific Oceans – and they drift in a circular motion towards the poles, due to traction resulting from the rotation of the planet. On Jupiter, on the other hand, strong jet currents prevent these storms from forming below 60º latitude – only above are the currents weak enough to allow cyclones to rage. What causes these particular storms on Jupiter to settle at 84 ° latitude? Jupiter’s cyclones are indeed attracted to the poles, according to the new study, but the polar storm in the center of the cyclone ring pushes them back, preventing them from reaching the pole itself.
“As long as cyclones stay away from the pole, they are attracted to it. But the closer they get, the more strongly they are repelled, ”explains doctoral student Nimrod Gavriel from the Kaspi research group, whose thesis focuses on elucidating this phenomenon. “The question is whether the repulsion effect is strong enough to resist the pull of the pole. Latitude 84º is where these forces intensify. Gavriel and Kaspi propose a mathematical model that considers the diameter of the polar cyclone (which is larger at the south pole than at the north), the minimum possible distance between each cyclone, the area around latitude 84º and the size of the cyclones and their size. rotation, and which accurately predicts the presence of eight cyclones across the North Pole. As for the South Pole, according to their calculations, the number of cyclones should be 5.62. This number is consistent with the data collected by Juno: in reality this number cannot exist, but the five southern storms often separate into six storms, as observed during the eighteenth and thirty-fourth orbits of the spacecraft around Jupiter. . The proposed model also explains why this phenomenon is absent on the neighboring planet closest to Jupiter – Saturn.
“We are trying to understand large-scale atmospheric dynamics, and providing a successful explanation of Jupiter’s polar cyclone phenomenon gives us the assurance that we really know what’s going on there,” Kaspi said. This confidence may be paramount to us here on Earth, as a better understanding of cyclones could help meteorologists predict, for example, how the warming of our planet will affect the movement of storms through it – a challenge humanity will be very much about. probably faced. in the near future. But Kaspi’s fascination with exploring Jupiter is simpler: “There are no new islands to discover in the Pacific, and most of the planetary bodies in the solar system have already been mapped. The poles of Jupiter and the other gaseous planets are perhaps the last points in the solar system that have yet to be explored.
The diameter of each of Jupiter’s cyclones is approximately 4,000 to 5,000 kilometers, and they rotate at speeds of up to 360 kilometers per hour.
“We expect more valuable data to arrive from Juno over the next two years,” Kaspi adds, following the recent extension of the Juno mission to 2025. “Due to incremental changes in the polar orbit of the spacecraft, it is now approaching and closer to the north pole of Jupiter, allowing us to obtain information on this polar region from several specialized instruments, ”he concludes.
Reference: “The Number and Location of Jupiter’s Circumpolar Cyclones Explained by Vortex Dynamics” by Nimrod Gavriel and Yohai Kaspi, July 19, 2021, Geosciences of nature.
DOI: 10.1038 / s41561-021-00781-6
Professor Yohai Kaspi is the director of the Helen Kimmel Center for Planetary Science.