Jupiter’s Great Red Spot Shimmies to a Beat

 

From - Sky & Telescope

By - Camille Carlisle

Edited by - Amal Udawatta

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)

(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.)

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.