For over 150 years, astronomers have been keeping an eye on Jupiter’s iconic Great Red Spot (GRS), a massive anticyclone that could fit our planet inside it. Yet, new discoveries continue to emerge—especially with the Hubble Space Telescope providing detailed observations.
Recent data gathered by Hubble over a 90-day period from December 2023 to March 2024 has unveiled that the GRS is less stable than previously thought. The findings indicate that the GRS exhibits movement similar to a wobbly bowl of jelly. By merging images from Hubble, scientists have created a time-lapse video showcasing the GRS’s erratic motions.
Amy Simon from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the lead author of a paper published in The Planetary Science Journal, noted, “While we knew its motion varies a little longitudinally, the oscillation in size was unexpected. To our knowledge, this hasn’t been observed before. This is truly the first time we’ve had the right imaging frequency to capture the GRS. With the high resolution of Hubble, we can confirm that the GRS is simultaneously contracting and expanding while changing speeds—this was surprising, and currently, there are no hydrodynamic explanations for it.”
Through the Outer Planet Atmospheres Legacy program (OPAL), which Simon leads, Hubble monitors Jupiter along with other outer solar system planets annually, but these specific observations were part of a targeted study of the GRS. By analyzing the largest storms in the solar system, researchers aim to place Earth’s hurricane theory in a broader cosmic framework, potentially enhancing our understanding of meteorological phenomena on exoplanets.
Simon’s team utilized Hubble to closely examine the GRS’s dimensions, form, and slight color variations. “When we scrutinize the GRS, we notice many changes occurring day by day,” Simon stated. Ultraviolet observations revealed that the storm’s distinct core brightens when the GRS reaches its maximum size in its oscillation cycle, implying reduced haze absorption in the upper atmosphere.
Co-investigator Mike Wong from the University of California at Berkeley explained, “As the GRS speeds up and slows down, it’s pushing against the strong jet streams located to its north and south. This can be likened to a sandwich where the bread bulges outward due to an abundance of filling in the middle.” He also contrasted this behavior to Neptune, where dark spots can shift dramatically in latitude without the restraint of powerful jet streams. For the duration of Earth-based telescopic observations, Jupiter’s Great Red Spot has remained fixed at a southern latitude, confined between these jet streams.
The research team has been monitoring the GRS’s shrinking size since the OPAL program launched 10 years ago. They anticipate it will continue to shrink before transitioning to a more stable, less elongated form. “Currently, it’s overextending its latitude band in relation to the wind field. When it eventually shrinks within that band, the winds will likely maintain its position,” Simon explained. Although they believe the GRS’s size will stabilize eventually, so far, Hubble has only captured data for one complete oscillation cycle.
The researchers are hopeful that future high-resolution images from Hubble will help uncover other Jovian characteristics that could explain the cause of the GRS’s oscillation.
These findings are being shared at the 56th annual meeting of the American Astronomical Society Division for Planetary Sciences in Boise, Idaho.
