Jupiter’s Great Red Spot is shrinking! But why?

Why is Jupiter’s Great Red Spot shrinking?

Astronomers have watched Jupiter’s Great Red Spot through their telescopes for hundreds of years. This giant storm was once the size of three Earths, but its size has shrunk, particularly over the last 50 years. Astronomers said on July 18, 2024, that the shrinking may be due to a lack of smaller storms to feed it.

Caleb Keaveney of Yale University led the research that used 3D simulations of interactions between the Great Red Spot and smaller storms. They found that nearby storms would strengthen the Great Red Spot, increasing its size. So the current shrinking spot may be due to a lack of smaller storms in its diet.

Notably, this interplay is similar to how heat domes work on Earth. These persistent high-pressure regions – like the Great Red Spot – can maintain their presence with the help of smaller weather systems nearby. Keaveney said:

Interactions with nearby weather systems have been shown to sustain and amplify heat domes, which motivated our hypothesis that similar interactions on Jupiter could sustain the Great Red Spot. In validating that hypothesis, we provide additional support to this understanding of heat domes on Earth.

The journal Icarus will publish the peer-reviewed paper on Jupiter’s Great Red Spot in its September 2024 issue.

More about the Great Red Spot

Jupiter is a gas giant planet with an atmosphere that teems with whorls and bands. The most famous feature on Jupiter is its stormy Great Red Spot, which has raged on the planet for hundreds of years. It’s a counterclockwise-moving storm – an anticyclone – with winds as high as 300 miles (480 km) per hour.

So, why has the Great Red Spot lasted so long? Well, without surface features, the storms on Jupiter don’t encounter friction like on Earth. Anyone who lives by a mountain knows that such features can cause storms to dump rain on one side and then dry up by the time they reach the other side. There are no such influences on Jupiter’s storms, so they rage for decades and centuries.

But the Great Red Spot is shrinking. Indeed, the storm we see today is smaller and rounder than what observers photographed and sketched in the past. And now, new research suggests the Great Red Spot we see now may not be the same one astronomers drew hundreds of years ago.

Images of Jupiter’s iconic storm from hundreds of years ago

We don’t know exactly how long people have seen the Great Red Spot. Robert Hooke may have spotted it in 1664. However, some people believe he was looking at a different storm. Also, the Great Red Spot we see today may be different from the storm observers saw in the 1600s. Below is a painting from 1711 showing the first depiction of the Great Red Spot as red.

From 1831 to 1879, there are 60 recorded observations of Jupiter’s Great Red Spot. From then on, observers have been continuously monitoring it. As an illustration, below is a sketch from 1881, showing how large and oblong it was at that time.

More recent observations

Here are more comparisons of the Great Red Spot – then and now – from photographic evidence. From an observation at Lick Observatory in 1891 (in Damian Peach’s post), to the Pioneer 10 and Voyager flybys of the 1970s, you can see for yourself that the storm has shrunk and taken on a rounder appearance over the years.

The Pioneer 10 images of Jupiter's Great Red Spot in 1973 were dramatic, since the storm was LARGE, and RED, surrounded by whitish clouds. The GRS today is still the largest storm in the Solar system, but it is now a shadow of its former glory. https://t.co/mTkoONz2GS pic.twitter.com/F0gYlZVWLv

— Dr Heidi B. Hammel (@hbhammel) November 24, 2023

From our EarthSky community

Here’s a wonderful shot of Jupiter with its Great Red Spot from our EarthSky global community. Do you have a photo of Jupiter to share? Send it to us!

Bottom line: Jupiter’s Great Red Spot is shrinking! A new study suggests the giant vortex has been eating fewer smaller storms, and this lack of fuel is causing it to decrease in size.

Source: Effect of transient vortex interactions on the size and strength of Jupiter’s Great Red Spot

Via Yale