Saturn's Bizarre Hexagon Vortex Just Got Even Weirder

An international team of scientists has revealed an intriguing new feature at Saturn's northern pole using data collected by the now defunct Cassini spacecraft, according to a study published in the journal Nature Communications.

The paper describes a hexagonal-shaped vortex which appears at the north pole near summertime high up in the gas giant's atmosphere, far above the clouds, in a layer known as the stratosphere.

The findings suggest two possibilities: The first is that the previously known hexagonal vortex seen much lower down in Saturn's clouds is actually a towering structure that extends far higher than previously thought, possibly spanning a vertical distance of hundreds of miles. The second is that two identical hexagonal vortices have spawned independently at different altitudes.

"The current study is surprising, because it shows that something we thought was only present in the cloud tops can actually persist to very high altitude," Leigh Fletcher, lead author of the study from the University of Leicester, U.K., told Newsweek.

Saturn's clouds are home to most of the planet's weather, including the previously known hexagonal vortex at the north pole.

This mysterious and iconic feature was first discovered by the Voyager spacecraft in 1981, "but it took some years for the discovery to come to light, as it required the stitching together of multiple images to make a complete map of Saturn's north pole," Fletcher said. "It's since been viewed by Hubble and from the ground but was then characterized in great detail by Cassini."

The hexagon is essentially a swirling system of air currents and turbulent weather which has lasted for decades and shows no sign of abating.

"It only looks like a hexagon when viewed from above, from high over the pole," Fletcher said. "The whole Earth would fit along one side of the hexagon, to give you an idea of its size. We think that it's a naturally-forming wave pattern, like the meandering of the jet streams that we see here on Earth, but it takes on this "perfect" six-sided shape because there's no topography—mountains, valleys, coastlines—to get in the way of the pure fluid flows."

"We haven't seen anything quite like it elsewhere, although the polar regions of all the planets often host surprises, from Jupiter's crown of circumpolar cyclones, to Venus's dipolar vortex."

Even though Cassini conducted extensive investigations of the hexagonal vortex deep in Saturn's north polar clouds, the spacecraft's infrared instruments were not able to reliably gather information in the northern stratosphere because temperatures there were too cold, meaning this region remained relatively unexplored for many years.

This, coupled with the fact that a Saturnian year is equivalent to roughly 30 Earth years, explains why the new high-altitude hexagonal vortex has only now come to light.

"Saturn only began to emerge from the depths of northern winter in 2009, and gradually warmed up as the northern hemisphere approached summertime," co-author Sandrine Guerlet from the Laboratoire de Météorologie Dynamique, France, said in a statement.

From 2014 onwards, however, researchers were able to use Cassini's infrared instruments to study the northern stratosphere for the first time as the atmosphere warmed.

It is now clear that Saturn's poles behave very differently. Data collected by Cassini early in its mission during the long southern summer showed that the south pole has a vortex both lower down in the clouds and at high-altitudes, although neither are hexagonal in nature. The southern vortex is also warmer and much more mature than the northern vortex. Consequently, both poles display very different dynamics.

According to Fletcher, this indicates either that there is a fundamental asymmetry between the poles which is not well understood, or that the north polar vortex was still developing in the last observations taken by Cassini before its demise.

Operators brought the mission to a dramatic end in September 2017, when the spacecraft took a controlled "death dive" into Saturn's atmosphere, disintegrating on entry. The probe beamed data back to Earth right until the very end—the analysis of which will continue for many years to come, no doubt providing us with more fascinating insights into the gas giant.

The existence of a hexagonal vortex high up in Saturn's stratosphere indicates that there is still much to understand about the workings of the planet's atmosphere. In Fletcher's view though, the findings suggest that there is a connection between the processes taking place at different altitudes.

"From my perspective, this shows that phenomena deep down in Saturn's weather layer can have a strong influence on the structure of the upper atmosphere—there's a connection between these two domains, so that they're not completely independent of one another," he said.

"It shows that giant planet atmospheres are complex and intricate systems evolving over vast spans of time, and that long-term datasets, like those acquired by Cassini, are absolutely necessary to understand them."