Enormous towering hexagon on Saturn baffles astronomers

A bizarre hexagon has appeared high in Saturn's atmosphere, and astronomers can't figure out how it got there.

It's much bigger than the one first spotted lower in the atmosphere in the 1980s, and could be a tower hundreds of kilometres tall.

The hexagon from above.
The hexagon from above. Photo credit: ESA

"While we did expect to see a vortex of some kind at Saturn's north pole as it grew warmer, its shape is really surprising," said Leigh Fletcher of the University of Leicester, studying data sent back to Earth by the Cassini-Huygens probe.

"Either a hexagon has spawned spontaneously and identically at two different altitudes, one lower in the clouds and one high in the stratosphere, or the hexagon is in fact a towering structure spanning a vertical range of several hundred kilometres."

Saturn's northern hemisphere is at the height of summer, after a decade in winter. It's believed the changing temperatures have something to do with the stratospheric clouds' strange shape, but something doesn't add up for astronomers studying it.

"A single, towering hexagonal structure that stretches up through the atmosphere would be unlikely given that wind conditions change considerably with altitude," the Cassini-Huygens team said in a statement.

"Waves like the hexagon should be unable to propagate upwards - they should remain trapped in the cloud-tops."

But the alternatives is equally baffling.

"Either a hexagon has spawned spontaneously and identically at two different altitudes, one lower in the clouds and one high in the stratosphere, or the hexagon is in fact a towering structure spanning a vertical range of several hundred kilometres."

Just as strange is no similar vortex has been seen at Saturn's southern pole - it's just a circle.

"This could mean that there's a fundamental asymmetry between Saturn's poles that we're yet to understand," said Dr Fletcher.

Why the shape is a hexagon and why it changes colours remains a mystery. Each of its sides is 14,500km long - nearly 2000km longer than the Earth is wide.

The Cassini-Huygens probe was in orbit around Saturn for 13 years - not quite half a Saturnine year.

The latest findings were published in journal Nature Communications.

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