Jupiter’s Great Red Spot is Wobbling and Fluctuating in Size, Hubble Observations Show

Astronomers using the NASA/ESA Hubble Space Telescope observed Jupiter’s most distinctive feature, the Great Red Spot, with on eight dates over a single, 90-day oscillation cycle from December 2023 to March 2024.

“While we knew its motion varies slightly in its longitude, we didn’t expect to see the size oscillate,” said Dr. Amy Simon, an astronomer at NASA’s Goddard Space Flight Center.

“As far as we know, it’s not been identified before.”

“This is really the first time we’ve had the proper imaging cadence of the Great Red Spot.”

“With Hubble’s high resolution we can say that the Great Red Spot 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.”

Dr. Simon and colleagues used Hubble to zoom in on the Great Red Spot for a detailed look at its size, shape, and any subtle color changes.

“When we look closely, we see a lot of things are changing from day to day,” Dr. Simon said.

“This includes ultraviolet-light observations showing that the distinct core of the storm gets brightest when the Great Red Spot is at its largest size in its oscillation cycle.”

“This indicates less haze absorption in the upper atmosphere.”

“As it accelerates and decelerates, the Great Red Spot is pushing against the windy jet streams to the north and south of it,” said Dr. Mike Wong, an astronomer at the University of California at Berkeley.

“It’s similar to a sandwich where the slices of bread are forced to bulge out when there’s too much filling in the middle.”

The authors contrasted this to Neptune, where dark spots can drift wildly in latitude without strong jet streams to hold them in place.

The Great Red Spot has been held at a southern latitude, trapped between the jet streams, for the extent of Earth-bound telescopic observations.

The astronomers predict it will keep shrinking before taking on a stable, less-elongated, shape.

“Right now it’s over-filling its latitude band relative to the wind field,” Dr. Simon said.

“Once it shrinks inside that band the winds will really be holding it in place.”

“We predict that the Great Red Spot will probably stabilize in size, but for now Hubble only observed it for one oscillation cycle.”

The team’s results were published in the Planetary Science Journal.

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Amy A. Simon et al. 2024. A Detailed Study of Jupiter’s Great Red Spot over a 90-day Oscillation Cycle. Planet. Sci. J 5, 223; doi: 10.3847/PSJ/ad71d1