Jupiter's Great Red Spot is a storm bigger than Earth, and it is shrinking.
Jupiter's famous red spot is a vast storm with winds up to about 500 km/h, watched continuously since 1878. A century ago it was around three times Earth's width. Now it is not much wider than our planet, and astronomers are arguing about whether it could fade away.
The Great Red Spot is a high-pressure storm, an anticyclone, sitting 22 degrees south of Jupiter's equator. It is the largest storm of its kind in the Solar System, spinning anticlockwise once every four and a half Earth days or so, with winds reaching around 496 kilometres per hour. Jupiter has no solid surface beneath its clouds, so there is nothing to create friction and slow the spin down, which helps explain how it has lasted so long.
Just how long is uncertain. Robert Hooke is often credited with spotting it in 1664, but he probably saw something else. Giovanni Cassini tracked a 'permanent spot' from 1665 to 1713, and if that was the same storm it would be at least 361 years old. But there is a gap of more than a century in the records, and a 2024 study concluded that Cassini's spot probably disappeared and today's formed later. The modern spot has been seen regularly since 1831 and continuously since 1878.
It is getting smaller. In the late 19th century it stretched about 40,000 kilometres; by 2017 it measured about 16,350 kilometres wide. In 2019 it seemed to shed fragments at its edge, prompting speculation that it could vanish within decades. Other astronomers argue that the visible clouds do not reflect the size of the vortex beneath, and that the flaking comes from encounters with smaller storms.
Its red-orange colour is put down to a kind of sunburn, as chemicals high in the storm are blasted by solar radiation. Spacecraft have given close views: Voyager 1 sent the first detailed image in 1979, and in 2017 the Juno probe flew about 8,000 kilometres above it. The storm also heats the air far above it, possibly through sound waves breaking in the upper atmosphere.
Source: Wikipedia — Great Red Spot · Text summarised from Wikipedia (CC BY-SA 4.0)
