Science & Technology

Why Does Saturn Have a Hexagon-Shaped Hurricane?

Windy weather can be the stuff of nightmares — just ask any fan of the "Sharknado" movies. And Earth isn't the only planet with tornadoes and hurricanes. Jupiter's Great Red Spot, for example, is a massive storm that's been churning for more than a century. And Saturn has a weird hexagon-shaped hurricane at its north pole. That's right: a storm with six equal sides. And new data shows this is a bigger storm than we thought, towering hundreds of miles in height.

A Vexing Hex

Clearly, this Saturn hurricane isn't the circle we're used to on Earth. It's got straight lines. Angles, even. That's really strange because we don't see a lot of straight lines in natural settings. (Unless we're talking about crystals, but that's another conversation.)

Scientists first uncovered Saturn's hexagon in 1988 after reviewing old data from two spacecraft called Voyager 1 and Voyager 2 that did quick flybys of the planet in 1980 and 1981. (In other words, this storm is at least 38 years old, which is weird in itself.)

Sending spacecraft to Saturn is a long and expensive process, so it wasn't until the Cassini mission arrived there in 2004 that we could confirm the hexagon really exists. And wow, did we learn a lot about it. Cassini stuck around at Saturn for 13 years and flew over the storm several times.

The hexagon is truly bizarre, and huge to boot. The structure (which includes a storm at the center) is roughly 20,000 miles (32,000 kilometers) wide, so big that you could plop down two Earth-sized planets inside and still have plenty of width to spare.

But for all our studies, we still don't know some of the basics — such as why this storm has straight sides to it, while on Earth our storms are more circular. Maybe it's the shape that resulted when two fluid bodies in the atmosphere, spinning at different speeds, met up with each other. Or maybe it has to do with wind jet speed and direction. Unfortunately, we have no spacecraft at Saturn anymore. But even though spacecraft die, their data live on.

Winter Is Fading

A new study based on old spacecraft data may help us move — or spin? — in the right direction to better understand the hexagon. Before, scientists thought the hexagon was buried down in the lower atmosphere, but the new study shows this weird storm actually extends 180 miles (290 kilometers) above the troposphere, reaching up into the stratosphere.

Here's where things get interesting. The data is based on information that flowed from Cassini during its entire mission, but Cassini could only get a really good look at the hexagon in the stratosphere starting in 2014. That's because some of its infrared (heat-seeking) instruments couldn't "see" the stratosphere during the northern winter when the temperatures were low. As the north warmed up, however, the hexagon started to show up in infrared wavelengths.

Seeing the same shape at a higher altitude completely floored the scientists. Here's the moment of realization as described by study co-author Sandrine Guerlet of the Laboratoire de Météorologie Dynamique in France: "As the polar vortex became more and more visible [in the stratosphere], we noticed it had hexagonal edges, and realized that we were seeing the pre-existing hexagon at much higher altitudes than previously thought," she said in a statement from the European Space Agency.

But why the hexagon? Scientists are still puzzled. They did see a storm in the warm southern hemisphere when Cassini first began its mission, but it sure wasn't a hexagon shape. There might be some kind of "fundamental asymmetry" between the north and south poles that explains the difference, the scientists say, but learning what that difference is may require another mission. To read more about the study, which was led by Leigh Fletcher of the University of Leicester, you can see the original Nature Communications paper here.

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For more up-close-and-personal views of the ringed planet, check out NASA's vivid book, "The Saturn System Through The Eyes Of Cassini." We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Elizabeth Howell September 10, 2018

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