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Unravelling the Mystery of Saturn’s Massive Hexagonal Storm

Hexagonal storm in black and white on Saturn
NASA/JPL-Caltech/Space Science Institute

In Saturn’s hydrogen and helium-rich atmosphere, a hexagonally shaped hurricane has been raging at the north pole. First observed in 1980, the storm measures about 20,000 miles across, at least 600 miles deep, and has winds reaching 300 miles per hour. But what causes its odd shape? Researchers think they may know.

Interplanetary Storm Chasing

The oddly shaped storm was first spotted by the Voyager spacecraft in 1981 and revisited by the Cassini-Huygens mission in 2006. It has puzzled astronomers for decades, although several theories have been put forth over the years. Research in 2015 postulated that the storm gets its shape from a jet stream flowing east in the planet’s atmosphere, which essentially flattens the typical circular pattern of such a weather phenomenon. In 2018, after analyzing data from the Cassini mission, researchers spotted a high-altitude vortex that matched the storm’s lower altitude vortex, which led to the idea that the storm might be tower-shaped.

Now, building on that previous research, two scientists out of Harvard University have tossed another theory into the ring regarding the hurricane.

In computer simulations, they’ve been able to show how a multi-sided monster storm could be formed when small vortices, or cyclones, form closer to the surface of Saturn and then rise and merge with the jet stream, which already contains its own share of storms, creating a pinching effect that shapes the storm.

“This jet is going around and around the planet, and it has to coexist with these localized [smaller] storms,” said research associate Rakesh K. Yadav, who works in Bloxham’s lab in Harvard’s Department of Earth and Planetary Sciences and is the study’s lead author.

Rubber Band Ball

“Think of it like this,” he continued. “Imagine we have a rubber band, and we place a bunch of smaller rubber bands around it, and then we just squeeze the entire thing from the outside. That central ring is going to be compressed by some inches and form some weird shape with a certain number of edges. That’s basically the physics of what’s happening. We have these smaller storms, and they’re basically pinching the larger storms at the polar region, and since they have to coexist, they have to somehow find a space to basically house each system. By doing that, they end up making this polygonal shape.”

While the simulation the researchers ran for a month produced nine-sided storms instead of six, they believe it still serves as proof of concept for how such a storm could form. Their work also leads them to agree with past research that says the storm is actually thousands—rather than hundreds—of miles deep. This would explain the effects of convection upwelling from deep in the planet’s atmosphere, creating vortices, and keeping the storm energized.

30-Year-Long Year

“The hexagonal flow pattern on Saturn is a striking example of turbulent self-organization,” the researchers wrote in their paper. “Our model simultaneously and self-consistently produces alternating zonal jets, the polar cyclone, and hexagon-like polygonal structures similar to those observed on Saturn.”

While researchers will no doubt continue to close in on how Saturn’s mysterious storm, they will mostly have to rely on data from Voyager and Cassini. That’s because direct telescopic observations are limited by Saturn’s weather and lengthy seasonal patterns. The planet takes a full 30 years to orbit our sun, half of which time the north pole is in darkness. Even when it is in full sun, the cloud cover can make it hard to see into the deep atmosphere.

The work has been published in the peer-reviewed journal, PNAS.