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The Cassini probe used its wide-angle camera to capture this image of the ringed planet Saturn on April 2, 2014. You can see hexagon – a strange feature with six sides – surrounding its circular northern polar vortex. Image via NASA.
Space scientists have been fascinated by the hexagonal nature of the north pole of Saturn since the Voyager mission first discovered it in 1981. It was thought that the hexagon – a jet into the atmosphere of Saturn at 320 km / h – was a feature of Saturn's lower atmosphere, or troposphere, only. Now, however, over the seasons of Saturn, this bizarre hexagon – wider than two Earths – seems to have changed. Writing in the peer-reviewed journal Nature Communications On September 3, 2018, scientists said they now have proof that the hexagon extends up to 300 km above Saturn's clouds, to the stratosphere of this world, at least during the spring and the summer of Saturn.
The new work is a long-term study, utilizing data from the Cassini spacecraft, which arrived at Saturn in 2004 and began observing the hexagon in 2006. Cassini's mission to Saturn has been completed. in 2017. to be for the coming years). Leigh Fletcher of the University of Leicester, UK, lead author of the new study, said:
The edges of this new swirl seem to be hexagonal, exactly matching a famous and bizarre hexagonal cloud that we see deeper into the atmosphere of Saturn.
While we were expecting to see some vortex at Saturn's north pole as it warmed up, its shape is truly surprising. Either a hex 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 that extends over several hundred kilometers.
Cassini captured images in 2012 that were used to create this animation of the Nordic polar hexagon of Saturn. Image via NASA / JPL-Caltech / SSI / Hampton / ESA University.
When Cassini arrived at Saturn in 2004, it was summer in the southern hemisphere of this world and winter in the northern half of the globe. Cassini saw a hot, wide, high-altitude vortex at the south pole of Saturn, but none at the North Pole of the planet.
In the years following Cassini's arrival at Saturn, the seasons moved to Saturn, whose orbit around the sun and whose seasonal cycle lasts 30 years. In recent years at Saturn, as summer approached the northern hemisphere, scientists saw a polar vortex at the North Pole of Saturn. The new work suggests that this vortex is also formed in the atmosphere, also hundreds of kilometers above the clouds, in the Saturn stratosphere.
Layers in the atmosphere of Saturn, via KHadley.com.
Just like on Earth, Saturn's troposphere – a lower layer of the atmosphere – is home to most of the planet's weather. It was thought that the northern polar hex was in the Saturn troposphere and was essentially a weather feature. A statement from the European Space Agency (ESA) explains:
This device was discovered by NASA's Voyager spacecraft in the 1980s and has been studied for decades. It is a long wave potentially related to the rotation of Saturn, a type of phenomenon also observed on Earth in structures such as the polar jet.
Its properties have been revealed in detail by Cassini, who has observed it in multiple wavelengths – from ultraviolet to infrared – using instruments, including its composite infrared spectrometer (CIRS). However, at the beginning of the mission, this instrument could not move higher in the northern stratosphere, which had temperatures around -158 degrees Celsius, or 20 degrees too cold for reliable IRS infrared observations. years.
Co-author Sandrine Guerlet of the Dynamic Meteorology Laboratory, France added:
A Saturnian year covers about 30 Earth years, so the winters are long.
Saturn only began to emerge from the depths of the northern winter in 2009 and has gradually warmed up when the northern hemisphere came close to summer.
As temperatures warmed around the north pole of Saturn, Fletcher and his colleagues were able to study the polar vortex in infrared light. Guerlet said:
We were able to use the CIRS instrument to explore the northern stratosphere for the first time from 2014. As the polar vortex became more and more visible, we noticed that it had edges We realized that we were seeing the preexisting hex at much higher altitudes than we previously thought.
Luminosity maps of the hexagonal stratospheric vortex at the north pole of Saturn via NASA / JPL-Caltech / University of Leicester / GSFC / L.N. Fletcher et al. 2018.
Scientists are fascinated by the differences between the two poles of Saturn. They said that there was no hexagon at the South Pole, nor at the top of the clouds, nor above, when it was observed at the beginning of the Cassini mission during the southern summer. The northern vortex is also not nearly as mature as the southern vortex because it is cooler and has a different dynamic from that of its southern counterpart. Fletcher said:
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 was still developing in our last observations and continued to do so after the disappearance of Cassini.
Cassini's long-standing mission was completed in September 2017.
These scientists also stated that:
… Understanding how and why the north polar vortex of Saturn has taken a hexagonal form will illuminate how deeper phenomena in the atmosphere can influence the environment above, which is of particular interest to scientists trying to understand how energy is transported in planetary atmospheres.
The northern hemisphere of Saturn spent its summer solstice in May 2017, shortly before Cassini plunged into the atmosphere of Saturn, thus ending her mission. The northern polar region is expected to continue to grow as the northern hemisphere moves to its fall equinox in 2024.
However, there is no spacecraft at Saturn now to get close observations of any subsequent changes in Saturn 's atmosphere. In this way, as in so many others, Cassini is missed.
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The hexagon of Saturn, in grayscale. Image via NASA / JPL-Caltech / Institute for Space Science. Learn more about this image.
Conclusion: It was thought that the hexagon at the North Pole of Saturn – a water jet-like element – was in a lower layer of the atmosphere, the troposphere, where most of Saturn's weather conditions occur. Exploring data from the Cassini spacecraft, European scientists have discovered that the hexagon extends up to 300 km above the clouds of Saturn to the stratosphere of this world.
Source: A hexagon in the northern stratosphere of Saturn surrounding the summer polar vortex
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