For a while we’ve known Saturn has a bizarre hexagonal storm at its north pole – but now we’ve discovered it’s even weirder than we thought.
Published in Nature Communications, scientists led by Leigh Fletcher from the University of Leicester in the UK used data from the Cassini spacecraft to study Saturn’s northern hemisphere. Here they found that a giant vortex sits high above the hexagonal storm – and it’s also a hexagon.
"The edges of this newly-found vortex appear to be hexagonal, precisely matching a famous and bizarre hexagonal cloud pattern we see deeper down in Saturn's atmosphere," Fletcher said in a statement.
The vortex sits about 290 kilometers (180 miles) above Saturn’s clouds, in a region of the upper atmosphere known as the stratosphere. The vortex appeared during the Cassini mission in 2014 as the northern hemisphere moved into its summer; a similar (but not hexagonal) vortex had previously been seen during the southern hemisphere’s summer.
Scientists were able to see this feature at the north pole for the first time with the Composite Infrared Spectrometer (CIRS) once the temperatures increased. And, as it came into view, they started to see how it closely matched the famous hexagonal storm.
"As the polar vortex became more and more visible, we noticed it had hexagonal edges, and realised that we were seeing the pre-existing hexagon at much higher altitudes than previously thought," co-author Sandrine Guerlet from the Laboratoire de Météorologie Dynamique in France said in the statement.
While interesting, this throws up a whole bunch of new questions. First and foremost is why jet streams on Saturn produce these hexagonal shapes, although there are some ideas. We don’t see them anywhere else, be that Earth or other planets, so what’s so special about Saturn?
The other question is whether this new hexagonal vortex is part of the storm below, or if it’s sitting on top. If the former, that means the entire structure is hundreds of kilometers in height. While this seems unlikely as wind conditions change a lot at different altitudes, a process known as “evanescence” may mean patterns like this could be maintained throughout the atmosphere.
"One way that wave 'information' can leak upwards is via a process called evanescence, where the strength of a wave decays with height but is just about strong enough to still persist up into the stratosphere," said Fletcher.
Unfortunately, answers to these questions might be hard to come by. The Cassini mission came to an end in September 2017, and Fletcher noted it was “frustrating” they’d only spotted this feature towards the end of the mission.
What is clear, though, is that Saturn is super weird. Cassini might be gone, but we’re still finding out some rather amazing things about the ringed planet thanks to its data.