Saturn’s hexagon may tower to the stratosphere
New findings based on Cassini data paint a stunning picture of the planet. Andrew Masterson reports.
An enormous hexagonal high altitude vortex above Saturn’s northern pole – captured by the international Cassini mission – might tower hundreds of kilometres above the planet’s clouds, researchers suggest.
When Cassini first reached Saturn in 2004 it recorded a high altitude vortex above the planet’s southern pole – then in the midst of summer – but nothing in the north. But now a fresh long-term study has identified a vortex structure forming as the northern hemisphere moves into its warmest season.
The vortex sits in the planet’s stratosphere, a long way above the clouds.
“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,” says Leigh Fletcher of the University of Leicester, UK, lead author of the new study.
Fletcher says that although he and colleagues expected to see some type of northern vortex, the shape came as a surprise.
“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,” he says.
Because of the extremely cold temperatures of the Saturnalian winter – reaching around minus-158 degrees Celsius at peak – Cassini’s infrared spectrometer was unable to make any observations of the planet’s north pole until spring arrived in 2014. A year on Saturn takes about 30 years.
"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,” says co-author Sandrine Guerlet from Laboratoire de Météorologie Dynamique, France.
The new findings are published in the journal Nature Communications, and are testament to the legacy of the Cassini mission.
“The Cassini spacecraft continued to provide new insights and discoveries right up to the very end,” says Nicolas Altobelli, ESA Project Scientist for the Cassini-Huygens mission.
“Without a capable spacecraft like Cassini, these mysteries would have remained unexplored. It shows just what can be accomplished by an international team sending a sophisticated robotic explorer to a previously unexplored destination – with results that keep flowing even when the mission itself has ended.”