Image credit: NASA
The Cassini probe detected this hexagonal-shaped vortex, very similar to the one discovered in the 1980s by the Voyager mission, shortly before it was destroyed.
Back in the 1980s, the American space probe Voyager discovered a cloud pattern located in the atmosphere of Saturn’s north pole which, given its shape, they named the Hexagon of Saturn and which could be linked to the rotation of this planet. Each of its six sides measures around 13,800 kilometers in length – a distance that, to give us an idea, exceeds 12,742 km in diameter of our Earth.
Now it has just been revealed that there is a second hexagon, a warm vortex with characteristics very similar to the first: it is also at the north pole of Saturn, although higher, in the stratosphere. The one in charge of detecting it was the international Cassini probe, which was part of a joint project of NASA, ESA and the Italian Space Agency (ASI) whose mission was to study Saturn and its moons. This discovery was made shortly before it was destroyed in September 2017 after entering the planet’s atmosphere.
The question that now arises for experts is the relationship that may exist between these two hexagons: are they completely independent of each other or could it be the same imposing structure that would span hundreds of kilometers in height?
By the time Cassini entered orbit around Saturn in December 2004, the southern hemisphere was enjoying summer, while the northern hemisphere was in the middle of winter, and no wide, warm high-altitude vortex was then detected here. As a Saturnian year spans about 30 Earth years, on Earth we had to wait until 2014 to observe that summer was beginning to timidly approach the northern hemisphere (the summer solstice did not arrive until May 2017).
Summer is coming
At last the conditions were beginning to be met for the different instruments with which Cassini was equipped to go to work. Before, it had not been possible due to the temperatures of 158 ° C below zero in the northern stratosphere, about 20 ° C below those required, for example, by one of those instruments designed to explore the area: the so-called Composite Infrared Spectrometer (CIRS, for its acronym in English), which measures infrared energy from the surfaces, atmospheres and rings of Saturn, as well as its moons, to study their temperature and composition. Since 2014, scientists have been able to use this tool to collect data.
And now, a long-term study, based on the CIRS observations, has discovered the first flashes of a vortex at the north pole forming above the atmosphere as the summer period rolled in.
The lead author of the research, Leigh Fletcher, from the University of Leicester (United Kingdom), explains that “the edges of this newly discovered vortex appear to be hexagonal, coinciding with the famous and strange pattern of hexagonal clouds that we see below, in the atmosphere of Saturn ”. “Although we expected to see a vortex of some kind at the planet’s north pole as it warmed up, its shape is really amazing,” she adds.
Faced with this singular discovery, the experts consider two possibilities: “Either a hexagon has been generated, spontaneously and in an identical way, at two different altitudes – one lower in the clouds and one higher in the stratosphere – or the hexagon is in fact a tall structure that spans a vertical range of several hundred kilometers, ”reveals Fletcher, who acknowledges that“ it is quite frustrating that this stratospheric hexagon was discovered just at the end of Cassini’s life, ”and not before.
Since the northern hemisphere passed the summer solstice in 2017 and the autumnal equinox won’t arrive until 2024, the researchers expect the north pole region to continue to develop in the years to come.