polar hexagon, Saturn

One year on Saturn is the equivalent of 30 years on Earth, so when it’s winter there, it’s a very long one. When the spacecraft Cassini first entered the Saturnian system in 2004, the planet’s northern hemisphere was locked in one of these winters, with temperatures at about -158 °C. It was far too cold for the probe to venture out. However, in 2014, Cassini became able to explore the northern stratosphere for the first time — a voyage that, according to a new study published in Nature Communications, revealed a spectacular vortex of air.

The finding is a result of a long-term study that comes nearly a year after Cassini was plunged into the planet it was surveying. In it, an international team of scientists announce that a warming, high-altitude vortex with a hexagonal shape lies hundreds of miles over Saturn’s northern pole during the planet’s summertime. Scientists were able to observe it via data obtained by the spacecraft’s Composite Infrared Spectrometer — but with Cassini now retired, what the vortex will do next is up to speculation.

“The mystery and extent of the hexagon continue to grow, even after Cassini’s 13 years in orbit around Saturn,” Cassini project scientist Linda Spilker, Ph.D. announced Monday. “I look forward to seeing other new discoveries that remain to be found in the Cassini data.”

Cassini
Cassini mission was a collaboration between NASA, the European Space Agency, and the Italian Space Agency.

This is not the first mysterious vortex observed floating above Saturn. Using data from Cassini, scientists previously pinpointed a vortex lurking above the southern pole during the planet’s warmer months. The edges of the two vortexes appear to precisely match, each sporting a hexagonal cloud pattern. But the northern vortex is smaller, cooler, and appears to display different dynamics.

“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,” study lead author and University of Leicester research fellow Leigh Fletcher, D.Phil., explained Monday. “Either a hexagon has spawned spontaneously and identically at two different altitudes, one lower in the clouds in the stratosphere or the hexagon is in fact a towering structure spanning a vertical range of several hundred kilometers.”

The scientists express frustration that they found the stratospheric hexagon at the end of Cassini’s lifespan because without more data, it’s hard to say what’s going on here for sure. Meanwhile, on Saturn, the weather continues to change, albeit extremely slowly — the autumn equinox won’t arrive until 2024.