Largest anticyclone in the Solar System

The largest anticyclone in the Solar System is the Great Red Spot (GRS), a storm that has been raging in Jupiter's southern hemisphere for at least 350 years. The most recent detailed images of the storm, taken on 4 September 2021 as part of the Hubble Space Telescope's Outer Planet Atmospheric Legacy (OPAL) program , found that the GRS was 14,893 km (9,254 mi) wide.

Wind speeds within the GRS are thought to reach as much as 435 km/h (270 mph). Data gathered by NASA's Juno spacecraft has revealed that the storm extends down through the cloud layers for around 350 km (220 mi).

The earliest detailed descriptions of the GRS date from the 1830s, but astronomers have been reporting sightings of a feature that may have been the GRS since the 17th century. Although it has been around for centuries, it is possible that we are witnessing the last phases of the storm's life. In 19th century descriptions, the GRS was estimated to measure around 40,000 km (24,800 miles) in width, but by the time the Voyager probes flew past the planet in 1979, it was only around 25,000 km (15,500 miles) wide. In recent years, the rate of decline appears to have accelerated. Data collected as part of the OPAL program in 2017 suggested it had shrunk to 16,350 km (10,159 miles), and this most recent measurement shows it has reduced in size even further. In May 2019, astronomers noticed long streamers of turbulent cloud extending thousands of kilometres downstream from the storm, suggesting that it may be beginning to break up. The storm is now only a little larger than Earth (which has a diameter of 12,742 km, or 7,917 mi).