The weird hexagon swirling around Saturn’s north pole is much taller than scientists had thought, a new study suggests.
Researchers have generally regarded the 20,000-mile-wide (32,000 kilometers) hexagon — a jet stream composed of air moving at about 200 mph (320 km/h) — as a lower-atmosphere phenomenon, restricted to the clouds of Saturn’s troposphere.
By Mike Wall
But the bizarre structure actually extends about 180 miles (300 km) above those cloud tops, up into the stratosphere, at least during the northern spring and summer, a new study suggests. [Stunning Photos: Saturn’s Weird Hexagon Vortex Storms]
The hexagon, which surrounds a smaller circular vortex situated at the north pole, has existed for at least 38 years; NASA’s Voyager 1 and Voyager 2 spacecraft spotted the sharp-cornered feature when they flew by Saturn in 1980 and 1981, respectively.
Scientists started to get much more detailed looks at the hexagon in 2004, when NASA’s Cassini spacecraft began orbiting the ringed planet. But Cassini’s hexagon observations were pretty much confined to the troposphere for a decade after its arrival; springtime didn’t come to Saturn’s north until 2009, and low temperatures in the stratosphere continued to compromise measurements by the probe’s Composite Infrared Spectrometer (CIRS) instrument for another five years.
“We were able to use the CIRS instrument to explore the northern stratosphere for the first time from 2014 onwards,” study co-author Sandrine Guerlet of the Laboratoire de Météorologie Dynamique in France, said in a statement from the European Space Agency (ESA).
Those observations have now been newly analyzed. And they revealed a surprise: the presence of a familiar shape high above the clouds.
“As the polar vortex became more and more visible, we noticed it had hexagonal edges, and realized that we were seeing the pre-existing hexagon at much higher altitudes than previously thought,” Guerlet added.
The formation of a stratospheric hexagon appears to be tied to the warming brought on by the change of seasons, the research team wrote in the new study. Indeed, Cassini spied a vortex high above the south pole during its early years at Saturn, when that hemisphere was enjoying summer. (Saturn takes 30 Earth years to orbit the sun, so seasons on the ringed planet last about 7.5 years apiece.)
But the southern stratospheric vortex wasn’t hexagonal. And neither, for that matter, is the vortex that spins around the south pole lower down, in the tropospheric clouds, the researchers said.
“This could mean that there’s a fundamental asymmetry between Saturn’s poles that we’re yet to understand, or it could mean that the north polar vortex was still developing in our last observations and kept doing so after Cassini’s demise,” study lead author Leigh Fletcher, of the University of Leicester in England, said in the same statement.
The new study was published online Monday (Sept. 3) in the journal Nature Communications.