Please pay! – Saturn Hexagon: 29,000 kilometer wide mysterious hexagon
The data and images from the Voyager probes continue to provide many insights today, but they raised even more questions, especially in the early days. One of them was revealed by Voyager 2 during its flyby of Saturn in 1981: When NASA scientist David Godfrey evaluated the photos in 1987, he noticed a huge polar vortex at the planet’s north pole – with a uniform hexagonal structure.
Polar vortices are actually not uncommon in the solar system – but a vortex with a symmetrical, hexagonal structure is. Was this a postcard from aliens, as conspiracy theorists were gloating, or was it just a natural phenomenon? The mystery of the Saturn hexagon was born.
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Almost 30,000 kilometers wide
The polar vortex is uniform and geometrically quite precise, with six sides approximately 14,500 kilometers long. With a diameter of 29,000 kilometers, it is more than twice the diameter of the Earth. The cloud pattern is something special: it moves at around 320 km/h, so that one rotation is completed in 10 hours, 39 minutes and 24 seconds.
The 1981 Voyager composite image stunned scientists. The hexagonal vortex can be clearly seen.
In the middle is a kind of eye of the storm, which is about 50 times larger than, on average, the already not exactly small terrestrial cyclones, which are otherwise only comparable visually. The cause of this geometric shape was initially completely unclear and fascinated scientists. However, since the Voyager probes were only in transit, the phenomenon could not be investigated in more detail.
Cassini probe provides more images
In 1997, the Saturn space probe Cassini-Huygens was launched, which was intended to further explore Saturn and, among other things, the North Pole hexagon. In 2004, the NASA probe entered Saturn’s orbit and began its work, but was not yet able to explore the hexagon: At that time, it was in the shadow on the side of Saturn facing away from the sun and could therefore only be explored to a limited extent.
The fairly exact hexagon-shaped vortex formation on Saturn’s north pole, captured here by Cassini.
(Image: NASA, JPL)
Since Saturn is much further away from the Sun than Earth, a Saturn year lasts 29 Earth years. A Saturn winter in which the hexagon was located lasts about seven years. In August 2009 the time had come: With the beginning of spring on the north side, Cassini was finally able to examine the North Pole optically.
After almost 20 years, the researchers asked themselves the following questions: What is the cause of the huge hexagon? Is the hexagon still the same as it was in the days of Voyager? Apart from the hexagonal shape, the polar storm is similar in structure to terrestrial cyclones, even if these form completely differently. Is such a hexagonal cyclone not possible here either?
Similar structure to terrestrial hurricanes
Kevin Baines, a scientist at NASA’s Jet Propulsion Laboratory involved in the Cassini program, described the polar vortex as having “at least the structure of a hurricane – it’s what we call the classic vortex structure.” However, there are crucial differences. Earth cyclones require the water and heat of the earth’s surface to form, which is not possible on a gas planet like Saturn. Due to its shorter distance, Earth also receives around 100 times more sunlight than Saturn.
The hexagonal vortex over time: on the left it was recorded by Cassini in 2013, on the right in 2017. The color changes are noticeable.
(Image: NASA, JPL)
Other differences such as the completely different day-night structure, the comparatively shallow atmosphere and the surface properties may prevent a similar phenomenon on Earth. However, the jet streams, the dynamic strong wind fields of the upper troposphere, have a similar hexagonal-like pattern, although not as uniform. On Saturn, these surface obstacles do not exist, which makes such perfect symmetry possible. And yet there are still many questions unanswered. For Baines, the polar vortex is “one of the greatest mysteries of Saturn’s dynamics.”
Another mini hexagon discovered
As if that wasn’t a mystery enough, in 2018, scientist Leigh Fletcher from the University of Leicester discovered a second hexagonal vortex in the Cassini data, which formed hundreds of kilometers above the well-known vortex from 2014 onwards. The researchers are wondering whether it may have been created because of Saturn’s summer. They also asked themselves whether it formed independently of the original hexagonal polar storm or whether there was a connection, which actually hardly seems possible. The color of the storm also changed over time.
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A team of researchers provided an explanation for hexagonal vortices back in 2010 by recreating such a natural phenomenon in the laboratory. In 2020, Rakesh Yadav and Jeremy Bloxham from Harvard University in Cambridge provided an explanation for vortices at Saturn’s north pole in simulations. Because the planet rotates more slowly at the pole than at the planetary equator, jet streams are created that move towards the poles. They have to share the surface with storms. “We have these smaller storms that basically crowd the larger storms in the polar region, and because they have to coexist, they have to somehow find a place to accommodate each system. That’s how you get this polygonal shape,” Yadaf said.
This makes the not-so-unique Saturn hexagon less mysterious, but certainly no less fascinating to look at.
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