Jupiter’s Great Red Spot Shows Unexpected Size Changes

Astronomers have been observing Jupiter’s legendary Great Red Spot (GRS), an anticyclone large enough to engulf Earth, for at least 150 years. But there are always new surprises, especially when NASA’s Hubble Space Telescope observes it up close.

New Hubble observations of the famous Red Storm, collected over 90 days between December 2023 and March 2024, reveal that the GRS is not as stable as it appears. Recent data shows that the GRS is shaking like a bowl of gelatin. The combined Hubble images allowed astronomers to assemble a time-lapse movie of the GRS’s wavy behavior.

“Although we know that its movement varies slightly in longitude, we did not expect to see its size oscillate. As far as we know, it has not been identified before,” said Amy Simon of the Goddard Space Flight Center of NASA in Greenbelt, Maryland. main author of the article published in The Journal of Planetary Science.

“This is really the first time that we have had the proper imaging rate of the GRS. With the high resolution of Hubble, we can say that the GRS is definitely moving in and out as it moves further and further quickly. It was very unexpected, and at present, there is no hydrodynamic explanation.

Hubble monitors Jupiter and the other outer planets of the solar system annually through the Outer Planet Atmospheres Legacy (OPAL) program led by Simon, but these observations came from a dedicated GRS program. Understanding the mechanisms of the solar system’s largest storms puts the theory of hurricanes on Earth in a broader cosmic context, which could be applied to better understanding the meteorology of planets around other stars.

Simon’s team used Hubble to zoom in on the GRS to get a detailed look at its size, shape and any subtle color changes.

“When you look closely, you see that a lot of things change from day to day,” Simon said. This includes ultraviolet light observations showing that the storm’s distinct core becomes brightest when the GRS reaches its largest size in its oscillation cycle. This indicates less absorption of haze in the upper atmosphere.

“As it accelerates and decelerates, the GRS pushes against windy jet streams to the north and south,” said co-investigator Mike Wong of the University of California, Berkeley. “It’s like a sandwich where the slices of bread are forced to expand when there’s too much filling in the middle.”

Wong compared this to Neptune, where dark spots can drift wildly in latitude without powerful jets to hold them in place. Jupiter’s Great Red Spot was located at a southern latitude, trapped between jet streams, for the extent of telescopic observations bound for Earth.

The team has continued to observe the decline of GRS since the OPAL program began 10 years ago. They predict it will continue to shrink before taking on a stable, less elongated shape. “Right now, its latitude band is too full relative to the wind field. Once it narrows inside that band, the winds will really hold it in place,” Simon said. The team predicts that the size of the GRS will likely stabilize, but for now, Hubble has only observed it during one oscillation cycle.

The researchers hope that in the future, more high-resolution images from Hubble can identify other Jovian parameters indicating the underlying cause of the wobble.

The results are being presented at the 56th annual meeting of the Division of Planetary Sciences of the American Astronomical Society, in Boise, Idaho.