As storms go, you don't get much bigger than the Great Red Spot raging across the surface of Jupiter.
This NASA handout image shows the Great Red Spot on Jupiter taken by the Juno Spacecraft on its flyby over the storm. Photo: AFP
The roiling clouds of the largest storm in the solar system could swallow Earth whole.
And the winds swirling around the outer edge are around twice as intense as a Category 5 cyclone.
Over the past decade, these winds have been picking up, according to new research published in the Journal of Geophysical Research.
And the spot is changing shape.
"It is becoming less cigar-shaped and more circular," said the study's lead author, astrophysicist Mike Wong of the University of California, Berkeley.
"If that trend just continues... then by 2035 to 2039 we may see it become fully circular."
The antics of Jupiter's weather systems have intrigued scientists and amateur astronomers for at least 150 years.
"I like that Jupiter's storms change all the time," said amateur astronomer Andy Casely, who takes photos of the giant planet from his backyard in Sydney.
"It really has weather in every sense of the word.
"The storms all move in relation to each other and new ones will pop up, the belts will change from month to month, year to year."
Although Jupiter's Great Red Spot has stayed roughly in the same latitude since it was first spotted in 1870, it has halved in size. And it's recently been through some turbulent times.
In 2016-17, another giant storm appeared nearby. Then in 2019, Dr Casely and a network of amateur astronomers around the world captured fragments of the spot flaking off.
"The red spot is normally just this round spot, [but we saw] it was misshapen," Dr Casely said.
"When we processed up the images, it was really obvious there were bits coming off it.
"We haven't really seen anything like that before, or since."
Finding 'a bit of a surprise'
To figure out what was going on, Dr Wong and his colleagues turned to the Hubble Space Telescope.
They analysed the movement of cloud features taken one Jupiter day - 10 Earth hours - apart in a series of high-resolution images taken between 2009 and 2020.
The observations showed the east-west width of the spot was shrinking by 1900km a year.
At the same time, wind speeds outside the red spot had picked up by 8 per cent over this time to about 370km/h.
Meanwhile, winds in the innermost ring were more akin to a breeze.
"[The finding] was a bit of a surprise," Dr Wong said.
Helen Maynard-Casely, a planetary scientist from the Australian Nuclear Science and Technology Organisation (ANSTO) who was not involved in the research, says the new study may help us understand why the spot is shrinking and whether the flaking event had anything to do with this.
"The red spot is a window into the dynamics of the Jovian atmosphere," Dr Maynard-Casely said.
"If we can understand it, then we can perhaps understand what is happening deeper and more globally too."
An illustrated Jovian moon Io, seen against the backdrop of Jupiter's Great Red Spot. Photo: AFP
Jupiter's weather systems are generated by heat rising from the interior of the planet.
"We know that heat is driving the motion, but we are still figuring out all the details of what that looks like," Dr Wong said.
Looking for clues on Earth
Clues to what might be happening in the red spot may be found on Earth in a phenomenon called "meddies".
These pancake-shaped vortexes of salty water flow out of the Mediterranean Ocean into the Atlantic, where they can linger for long periods.
"One of these meddies shrank over the period of a year and also sped up so we wondered if there could be some common processes," Dr Wong said.
Unlike vortexes meandering through Earth's oceans, the Great Red Spot is trapped between two bands of storms, above and below, spinning in the opposite direction.
Dr Wong said it could be possible that when storms on Jupiter drift around, they mix up their surroundings.
This could explain what has been happening to the spot over the past few years.
"We can't prove that the [appearance of the new storm nearby in 2016-17] was related to changes in the winds in and around the Great Red Spot at the same time, but it is intriguing that it happened at the same time," Dr Wong said.
It is also in line with observations made by amateur astronomers, including Dr Casely, of the flaking event.
Initially, there was speculation the "flaking" of bits off the side indicated the spot was disintegrating.
But in research published in the Journal of Geophysical Letters earlier this year, scientists said the event was not a sign the spot was falling apart.
Instead, it was caused by a series of smaller storms drifting across the top of the red spot.
"The surface events on the spot weren't really threatening to break apart the [red spot], because it was much bigger and deeper and more organised than that," said Dr Casely, who was recognised in the paper.
"It's just amazing to collaborate with professionals, to be a relatively average person in a backyard and be able to do some very real science."
-ABC