Future Technology
A ten sided shape has appeared at Saturn's south pole
Key takeaways
- Saturn's north pole has a long lived hexagonal jet stream, first imaged by Voyager and tracked closely by Cassini.
- A ten sided polygonal structure has now been identified at the south pole, where no stable polygon was previously established.
- Polygonal jets form when a fast circumpolar wind goes unstable in a regular, repeating way. The number of sides depends on the wind profile.
- Nobody observed the transition, because there has been no orbiter at Saturn since Cassini ended in 2017.
Saturn's north pole has a hexagon. It is one of the strangest stable features in the solar system: a six sided jet stream roughly 30,000 kilometres across that has held its shape since Voyager photographed it in 1981 and that Cassini mapped in detail for thirteen years.
The south pole never had a clean equivalent. It had a hurricane like vortex and a mess of fast moving cloud bands. Now analysis points to a ten sided structure there, a decagon, circling the southern pole. If it holds up, Saturn has two polygonal jets with different numbers of sides at the same time.
Why a planet grows corners
Nothing is bending the atmosphere into a shape on purpose. A polygonal jet is what happens when a fast ring of wind circling a pole becomes unstable and the instability repeats at regular intervals around the circle. The wave pattern locks in, and the meandering jet traces out straight looking segments with corners between them.
The number of sides is set by the physics of the jet: its speed, its width, and how sharply wind speed changes with latitude. Laboratory tanks of spinning fluid reproduce this readily, and you can change the polygon from a triangle to a nonagon just by changing the rotation rate. A hexagon in the north and a decagon in the south implies meaningfully different circumpolar wind profiles at the two poles, which is interesting, because Saturn receives very similar sunlight at both over a full orbit.
Season is the obvious suspect. A Saturn year is about 29.5 Earth years, so each pole spends roughly fifteen years in summer and fifteen in winter. Cassini arrived in 2004 with the southern hemisphere in summer and left in 2017 with the north lit. Whatever reorganised the southern jet may simply be the second half of a cycle nobody has watched all the way through.
The uncomfortable part
There has been no spacecraft at Saturn since Cassini's deliberate plunge into the atmosphere in September 2017. Everything since comes from Earth based and space based telescopes looking at a planet a billion kilometres away. A structure that large appearing unnoticed is a reminder that our continuous record of the outer solar system ended nine years ago and has not restarted.
Dragonfly is heading to Titan later this decade, which will put hardware back in the Saturn system, though it is a Titan mission and not a Saturn atmospheric one. Proposals for a Saturn orbiter or atmospheric probe keep being written and keep losing budget fights to Mars and the ice giants.
Seeing Saturn yourself
You will not see the decagon from a back garden. It sits almost directly over a pole, and resolving polar detail needs either a large telescope and excellent conditions or a spacecraft. The rings and the four brightest moons are a different matter, and they are genuinely striking in modest optics.
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A steady pair of wide aperture binoculars will show Titan as a clear point beside the planet on any decent night. The Celestron Cometron 7x50 is the cheapest honest way in, and the 50mm front glass matters far more than magnification for this.
The broader point stands regardless of kit. A gas giant quietly rearranged a polar jet stream the size of several Earths, and the first anyone knew of it was an analysis pass years later. The solar system does not wait for us to be looking.
