Jupiter is well known for its Great Red Spot, a feature that was discovered by Galileo over 400 years ago! Astronomers have been tracking the size and shape of it for over a century but the most accurate measurements have come from the Hubble Space Telescope. Every time Earth and Jupiter are at their closest, Hubble takes a series of images and it's these images that have detected that the spot jiggles from day to day. Not only does it change size but length and width too leaving astronomers baffled.

Jupiter is the largest planet in the Solar System and, like the other outer planets, is a giant ball of gas. It's so large all the other planets in the Solar System can be fitted inside with plenty of room to spare. Composed mostly of hydrogen and helium, it can be seen as a colourful disk through amateur telescopes with belts, storms, and of course the Great Red Spot. The spot was first discovered by Galileo in around 1610 when he became the first person to turn a telescope on the distant planet.

The Great Red Spot is an astonishing storm that has been raging for over 400 years. It's large enough that Earth could easily fit inside more than once, operating as an anticyclone system similar to what we observe on Earth. This massive storm rotates in a counterclockwise direction with wind speeds reaching in excess of 640 km per hour. Compellingly, while it has generally decreased in size over the years, it has not diminished as swiftly as scientists once projected.

Recent imaging taken by the Hubble Space Telescope between December 2023 and March 2024 captured the Great Red Spot at a time when Jupiter was particularly close to Earth. These high-resolution cameras revealed that the storm exhibits a unique behavior, jiggling like a bowl of jelly. This suggests a dynamic instability that challenges our previous understanding of this longstanding atmospheric phenomenon (Simon et al., 2024).

Previous observations of the Great Red Spot primarily focused on its longitudinal movement; however, they provided no definitive evidence of changing size. The groundbreaking study led by Amy Simon at NASA's Goddard Space Flight Centre underscores the importance of real-time, high-frequency imaging in understanding this planetary phenomenon. According to Simon, "This is really the first time we've had the proper imaging cadence of the GRS. With Hubble's high resolution, we can say that the GRS is definitively squeezing in and out at the same time as it moves faster and slower. That was very unexpected, and at present, there are no hydrodynamic explanations" (Simon et al., 2024).

This observation challenges the static conception of the Great Red Spot, providing new data that may lead to a reassessment of how we understand such massive storms. It should be noted that this investigation was part of NASA's Outer Planet Atmospheres Legacy program (OPAL), which aims to gather a long time series of observations of the outer planets to enhance our understanding of their evolution and atmospheric dynamics. Although the recent observations were focused on the GRS, they represent significant progress in planetary atmospheric research.

Extrapolating from the current findings, researchers posit that the Great Red Spot will continue to shrink in size but eventually stabilize into a less elongated shape. At its current dimensions, it is notably wide in latitude. Once it diminishes in size, it is expected to stabilize, with the winds playing a crucial role in maintaining its structure. The future of the GRS is pivotal not only for our understanding of Jupiter but also for refining our knowledge of storm systems in general.

Such findings hold implications beyond the gas giant itself, potentially providing insights into Earth's own hurricane systems. Understanding the mechanisms behind the GRS could illuminate the forces driving storms on our home planet, helping scientists to predict severe weather events more accurately (Simon et al., 2024).