Three great storms | Day 9

We, the inhabitants of Earth, are living in rather cushy weather conditions. While storms do emerge on our planet fairly often, even the most massive ones are still puny (and short) compared to the impressive weather that some of our nearby planets experience. Today I look at some remarkable storms on three of the gas giants in the outer reaches of our solar neighbourhood.

Jupiter’s Great Red Spot

Likely the most famous storm in the Solar System is the gigantic one raging on our biggest planet, Jupiter. Observations of the Great Red Spot go back to as far as the 17th century, so it appears that this anticyclonic marvel of a hurricane has been tearing about for at least 300 years.

The anti-clockwise rotation of this storm takes six Earth days to complete, and its diameter is so huge that you could easily fit several Earth-size planets in there. Furthermore, the winds around the edges of the storm reach 432 km/h, although that is only somewhat impressive, as you’ll see further on.

The spot is definitely a signature feature of the hydrogen-helium giant as we know it, however it is also shrinking. In the decade between 1996 and 2006 Jupiter’s storm lost 15 per cent of its diameter. It is not yet clear whether the storm will one day dissipate completely, or whether the shrinking is just part of regular fluctuations.

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Swirling clouds close-up from Voyager 1 | NASA/JPL
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Jupiter’s portrait from Cassini | NASA/JPL/Space Science Institute

Neptune’s Great Dark Spot

Akin to Jupiter’s massive blemish, the gorgeous methane-blue Neptune has similar occurrences on its hazy surface. Every few years or so an elliptical, dark spot emerges about the size of Earth.

We first saw evidence of this phenomenon in 1989 when images from the Voyager 2 space probe arrived. That storm has since dissipated, but according to further research from Hubble, it appears that Neptune has one of these spots more than half of its time. Astronomers believe that these massive anticyclones are caused by a temperature difference between the frigid clouds in the atmosphere and the heat-producing rocky core of the planet.

Despite the serial nature of this event, humans have named this storm series the Great Dark Spot. However, by far the most impressive thing about this storm is the wind speed — it has been measured at as much as 2,400 km/h. That’s way faster than anywhere else in the Solar System.

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Neptune’s storms | NASA/Voyager 2 Team
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Neptune whole planet portrait from Voyager 2 | NASA Planetary Photojournal

Saturn’s Hexagon

It’s no surprise that most of what we know about the far reaches of our solar system comes from the Voyager missions. In 1981 Voyager 1 space probe passed Saturn for the first time, and sent back some astonishing footage of a strange vortex encompassing the planet’s north pole. Never before had we observed such a neatly geometrical object anywhere else in the Solar System.

This cloud pattern, shaped like a hexagon, is enclosed by a jet stream and extremely stable in its movement, while inside it there are winds of over 400 km/h tearing about. Each side of the hexagon is roughly 13,800 kilometres long; for contrast, Earth’s whole diameter is only 12,742 km.

Nobody knows how long the hexagon has been there, but there are some clues to how it could have formed in the winds of the hydrogen gas giant. Humans have been able to replicate similar shapes in a laboratory when rotating a round tank of water with a base split into circular sections. When the liquid was rotated at increasingly different speeds at the centre and edges — the geometric shape emerged on the turbulent boundary between the two rotating bodies of water. Furthermore, experimenting with various speed differences they were also able to create other shapes, such as triangles and septagons. Of course, the original vortex is still more spectacular than anything we can create in a tiny laboratory.

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Saturn’s north pole view from Cassini | NASA/JPL-Caltech/Space Science Institute
Hexagon in natural colour | NASA/JPL-Caltech/Space Science Institute
Hexagon in natural colour | NASA/JPL-Caltech/Space Science Institute

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