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Nearly a year after diving into Saturn's atmosphere and ending its mission, NASA's Cassini spacecraft continues to provide new and intriguing information about the ringed planet. A few months ago, the captured data gave a glimpse of the Saturnian moon Titan, and now we are looking at a strange feature on the North Pole of the gas giant.
The characteristic referred to is a vortex – a rapidly moving stream of air – that swirls nearly 300 kilometers above the clouds of the summit of Saturn in an atmospheric layer called the stratosphere.
When Cassini arrived in the vicinity of Saturn in 2004, he closely examined the North and South poles of the planet. During these observations, the spacecraft discovered a high-altitude vortex in the southern hemisphere, which was experiencing the summer, but could not find similar signs in the colder regions of the north.
The latest discovery changes this observation and confirms the presence of a hot vortex 20,000 miles wide on the North Pole. These data come from when the North Pole closed during the summer season. However, what is interesting is that the vortex seen has a strange hexagonal shape, something that looks a lot like a cloud model seen at much lower altitudes in an atmospheric layer called the troposphere.
"While we were expecting to see some vortex at Saturn's North Pole as it warmed up, its shape is really surprising," said Leigh Fletcher, lead discovery scientist, in a statement. "Either a hexagon appeared spontaneously and identically at two different altitudes, one lower in the clouds and the other in the stratosphere, or the hexagon is actually an imposing structure covering a vertical extent of several hundred kilometers.
The hexagon present at the cloud level was first observed by the Voyager missions in the 1980s and was then analyzed in detail by Cassini. Scientists, who observed the phenomenon, confirmed its connection with Saturn's rotation, but for a long time, Cassini's observation techniques were limited to the lower atmosphere. The upper region or stratosphere had temperatures around -158 degrees Celsius, which was far too cold for its instruments to produce reliable results.
"A Saturnian year covers about 30 terrestrial years, so the winters are long," said co-author Sandrine Guerlet of the Laboratory of Dynamic Meteorology of France, in the same release. "Saturn did not begin to emerge from the depths of winter in the north until 2009 and gradually warmed as the northern hemisphere approached."
At that time, the researchers had the opportunity to take infrared observations of the stratospheric region, which revealed the presence of the same hexagonal swirl – much higher.
"[When] the polar vortex was becoming more and more visible, we noticed that it had hexagonal edges and we realized that we were seeing the pre-existing hex at much higher altitudes than previously thought Added Guerlet.
Researchers believe that vortices at both poles behave very differently from one another. The whirlwind of the South Pole does not have hexagonal ridges, while those in the north have a weird shape and are much cooler in comparison, indicating that it is still not as mature as its siblings.
"This could mean that there is a fundamental asymmetry between the poles of Saturn that we have not yet understood, or that the northern polar vortex has continued to develop in our last observations and continued after the disappearance of Cassini" , concluded Fletcher. Further analysis of the Cassini data could provide more information on two vortices, including the reason for the strange hexagonal shape.
The study entitled "A hexagon in the northern stratosphere of Saturn surrounding the emerging summer polar vortex" was published on September 3 in the journal Nature Communications.
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