Jupiter’s Great Red Spot moves Like the solar system’s biggest kickball

The Great Red Spot of Jupiter is one of the solar system’s most astonishing marvels. An elliptical storm with inky swirls of burnt orange and dulled copper, it is longer than the Earth is wide, and its winds screech through the tops of the planet’s clouds at 400 mph.

The spot may seem like an unchanging fixture from a distance. But scientists have now discovered that it is jiggling and changing shape, repeatedly elongating and then contracting as it circumnavigates Jupiter’s southern hemisphere like a bright red kickball bouncing through a schoolyard.

Astronomers say that the Great Red Spot hasn’t always looked as it does today. But finding that it was able to transform during a 90-day period of observation came as a shock. “We were very surprised,” said Amy Simon, a planetary astronomer at NASA’s Goddard Space Flight Center and an author of a study published this week in The Planetary Science Journal.

While it’s possible to see something ball-like in the locomotion of the Great Red Spot, some scientists see a living creature. The storm “behaves like a slug, contracting and stretching as it moves around the planet,” said James O’Donoghue, a planetary astronomer at the University of Reading in England who wasn’t involved with the study. “It’s a Great Red Slug.”

Whatever one thinks it mimics, astronomers have no clue as to why the spot is behaving this way. “It is a mystery how this process works in terms of the underlying physics,” O’Donoghue said.

The Great Red Spot, which rotates counterclockwise, has been continuously observed for the past 150 years. It probably hasn’t always been present on Jupiter, at least not in its current form, and its origins are not clear.

That the storm has been around so long probably has something to do with two potent jet streams sandwiching it in place, O’Donoghue said. They keep the spot’s edges spinning while also preventing the storm from wandering off toward the equator or poles, where atmospheric forces and the planet’s rotation could tear it apart.

But the storm isn’t rooted in place. It “drifts slowly westward, taking a few years to circle the planet,” Simon said. And as it migrates, it speeds up and slows down over a three-month cycle. This cycle, observed for decades, has yet to be explained.

Is the storm doing anything else strange as it repeatedly hits the gas, and then the brakes, during these 90-day increments? To find out, Simon and her team observed the Great Red Spot from December 2023 through March 2024 using the Hubble Space Telescope.

During that 90-day cycle, they were stunned to see the storm changing size. When it drifted at a more leisurely pace, the spot stretched out; when it moved more hastily across Jupiter, it squished back up and became more compact.

The fact that the spot changed form so periodically was certainly curious. But even if the team couldn’t explain why this was happening, it already knew the superstorm had shape-shifting abilities.

“Such an elongated shape is not very stable,” Simon said. In the late 1800s, the storm was more than three times wider than Earth, and it has been rapidly shrinking ever since. It could be that as nature’s forces push it to seek a more ideal shape, the Great Red Spot may vanish.

Ultimately, this close-up by the Hubble highlights that the Great Red Spot, like almost everything in the solar system, is ever-changing — a temporary display of beauty that we are fortunate to witness.

This article originally appeared in The New York Times.

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