Jupiter’s spectacular surface is further embellished by a vast cosmic wonder, a signature feature that wonderfully complements the planet’s majestically colourful layers. The largest known storm in the Solar System, Jupiter’s Giant Red Spot has always been exceedingly fascinating since its discovery in 1655 by Italian astronomer Giovanni Cassini. Located below Jupiter’s southern equatorial belt, it is Jupiter’s only permanent storm, persisting for 350 years. It has been changing appearance, however, every now and then, yielding varyingly contrasting colours in the process. In the 70s, it was quite large and was a deep red tinge. By the 80s, however, it had become a light pinkish hue before changing to gray and receding to red once more and then finally turning into salmon-like orange. It is a very intriguing structure particularly with regards to how it changes in appearance, size, and position and also with regards to the violent disturbances that it so intriguingly subsumes.

Jupiter’s Turbulent Nature and Raging Storms 

Jupiter’s atmosphere is a particularly turbulent one, exhibiting rapid jet streams, intricate circulation patterns, and various rotating structures.  The causes of Jupiter’s Great Red Spot remain contested. It was first proposed in the 60’s that the red spot could be the result of a vortex possibly brought about by the presence of some sort of an elevated feature (solid hydrogen tableland) on Jupiter’s surface that rotates with the planet and disrupts atmospheric currents flowing over it. However, the fact that the red spot wanders continuously in longitude is suggestive of the idea that it could in fact be floating in Jupiter’s cloud-rich atmosphere. The relative conspicuity of the spot would then be dependent upon how the spot changes in depth, as determined by whether the spot rises above or sinks below the clouds layers, which would also explain the apparent variety of colours elicited.   The spot appears to constitute vortex-like winds spinning around a relatively stable area. It is thought that the spot could be powered by some internal heat source from Jupiter. Intriguingly, the region located to the left of the red spot is a region of immense cloud formation activity and ammonia ice composition, whose turbulent nature is a most likely the resultant of powerful convection. The convective activity therein is suggested to transport internal heat up through the cloud layers. The Great Red Spot itself is nested within jet streams to the north and south of the region, which adds energy to the spot and keeps it in persistent operation. It is an anti-cyclone that spins in a counterclockwise fashion with a high pressure centre. Although Jupiter also harbors cyclones, anti-cyclones are the predominant rotating structures. The planet is replete with constant interactions between high pressure and low pressure systems that lead to lots of other thunderstorms all over the surface.

Quite intriguingly, the great red spot does slowly move and rotate around the surface of Jupiter, currently at 0.4 degrees per month. In the past century, it has performed about 3 circuits around the planet.

Although the causes of the red spot cannot be ascertained definitely, recent experiments by NASA JPL scientists have shed light on a quite possible scenario. The researchers mimicked the same cloud conditions in Jupiter’s atmosphere by creating clouds of ammonia and acetylene gases and sparking them with ultraviolet light in order to simulate the possible effects of the sun on Jupiter’s upper atmosphere. The mixture produced a reddish hue, comparable to that of the red spot, as observed by Cassini’s Infrared Mapping Spectrometer. This, combined with the suggestion of contrastingly lighter cloud layers below the reddish upper ones at the top, seem to call into question the hypothesis that the reddish hue of the red spot is due to chemicals being upwelled from below. Such a hypothesis posits that the colour of the spot comes from compounds like phosphorus or sulphur being upwelled from below.

The Not-So Red Spot

The great red spot has been varying its colour, quite remarkably indeed. Sometimes, it would manifest itself in a dark red colour. At other times later on, it would recede to a light pinkish hue or even camouflage itself inconspicuously with the Jovian surface. But the deep red colour, first prominent in 1880s, is no more at the moment. Since 1997, the spot has been rather faint and has reportedly been taking on the colour of a salmon-like orange hue.

The Not-So Great Spot 

The great red spot has been shrinking since the 1930’s. But, in 2012, the rate of shrinkage sharply increased in a pronounced manner, receding by 932 kilometres a year. In 2014, the Hubble Space Telescope captured a photo of Jupiter, which showed the red spot downsizing in an immense manner. The spot was once so large you could fit three Earths in it. In 2014, it had receded such that you could only fit one Earth in it. This is a marked decrease from its size in the 1800s, when it measured at 41000 kilometres across. It is now less than half that size.

New Hubble footage has shown that the spot is shrinking still further but at an albeit smaller rate and that it is now just the size of an orange pimple. It has shrunk to be 240 kilometres smaller than it was in 2014. The new footage also shows that the centre of the spot has developed a fine streamer distorted by winds moving at 150 metres per second.

At the current rate of reduction, it is predicted that by 2040, the red spot will become circular rather than oval, although this cannot be uttered with certainty.

It is not known definitely what could have possibly caused the red spot to recede in size, as demonstrated by Hubble’s latest findings. But, further footage/missions may shed light on this immense cosmic wonder.

Notwithstanding Jupiter’s magnificently resplendent appearance, it is undoubtedly an incredibly turbulent world, full of vast wonders yet to be explored. A weather forecast of Earth would most likely excite my suspicions but I would have absolutely no reason to doubt a Jovian weather forecast that says: “windy” 🙂

Featured image courtesy of: NASA/Björn Jónsson. Image from Voyager 1 spacecraft, taken in 1979.