Jupiter’s Great Red Spot Shimmies to a Beat

By: Camille M. Carlisle October 10, 2024 1

Hubble observations reveal that the storm’s size and shape change in a cyclic pattern.

The Great Red Spot has a jiggle.

The iconic storm has marred Jupiter for generations. Over time, the spot has changed in color and size, shrinking dramatically to less than half the size it had a century ago. Currently, it’s roughly the width of Earth, making it a fairly small blemish on the gas giant’s face.

The Great Red Spot doesn’t move in lockstep with the atmosphere around it. It slowly drifts westward, rolling like a ball between the surrounding bands of alternating winds. It laps the planet over the course of a few years.

Eight images of the giant planet Jupiter spanning approximately 90 days between December 2023 and March 2024. The planet appears striped, with brown and white horizontal bands of clouds. — Using Hubble Space Telescope data spanning approximately 90 days (between December 2023 and March 2024) when the giant planet Jupiter was approximately 740 million kilometres from the Sun, astronomers measured the Great Red Spot’s size, shape, brightness, colour, and vorticity over a full oscillation cycle. The data reveal that the Great Red Spot is not as stable as it might look. It was observed going through an oscillation in its elliptical shape, jiggling like a bowl of gelatin. The cause of the 90-day oscillation is unknown. The observation is part of the Outer Planet Atmospheres Legacy program (OPAL).
*NASA, ESA, A. Simon (GSFC)*

But the storm doesn’t drift at a constant rate. Astronomers have long seen an intriguing oscillation in the Great Red Spot’s glide, with the spot regularly speeding up and slowing down over a 90-day period. It’s like the storm is easing on and off the gas pedal as it moves.

The Great Red Spot isn’t the only storm in the solar system to do this: Neptune’s dark spots also oscillate, and on the same 90-day cycle, Amy Simon (NASA Goddard Space Flight Center) said October 9th during a press conference at the Division for Planetary Sciences meeting in Boise, Idaho. But Neptune’s storms slosh around, changing their tilt and crossing latitudes. The Great Red Spot stays steady at the same longitude and angle, held in place by the jet streams (the horizontal “stripes” to its north and south).

This time-lapse movie is assembled from Hubble Space Telescope observations spanning approximately 90 days (between December 2023 and March 2024) when the giant planet Jupiter was approximately 740 million kilometres from the Sun. Astronomers measured the Great Red Spot’s size, shape, brightness, colour, and vorticity over a full oscillation cycle. The data reveal that the Great Red Spot is not as stable as it might look. It was observed going through an oscillation in its elliptical shape, jiggling like a bowl of gelatin. The cause of the 90-day oscillation is unknown.
NASA, ESA, A. Simon (GSFC)

To better understand the oscillation, Simon and her colleagues pointed the Hubble Space Telescope at the Great Red Spot for a full 90-day cycle. They found that the spot’s size and shape vary over this same time period: The spot is widest and most oval-shaped when it’s moving slowest, and it’s narrowest and most circular when it’s moving the fastest. They also saw changes in the storm’s color and its core.

Notably, the winds raging inside the storm didn’t follow the same pattern.

Astronomers don’t know why 90 days is the sweet spot, nor why this period would apply to both Jupiter and Neptune, Simon said. Jupiter is almost three times larger than Neptune. “So there’s some fundamental characteristic of the rotation and deep structure of these planets that’s setting that 90 days.”

The research also appears in the Planetary Science Journal.

About Camille M. Carlisle

Science Editor Camille M. Carlisle handles science features for Sky & Telescope. She specializes in black holes, Mars, and whatever she happens to be writing about at the time. Frolic with her through the delights of black holes in her blog, The Black Hole Files.

Comments

Anthony Barreiro

October 12, 2024 at 12:43 am

When you say the Great Red Spot moves westward relative to the cloud bands, does that mean westward on Jupiter's surface, to the left in these north-up images? Not celestial west, which would be in the opposite direction? Just trying to make sure I'm picturing it correctly. The Great Red Spot is a high-pressure system, a southern-hemisphere anticyclone, so it rotates counterclockwise.

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