The largest storm in our solar system is moving unexpectedly, scientists say

By Ashley Strickland, CNN

(CNN) — New observations of Jupiter’s Great Red Spot captured by the Hubble Space Telescope show that the 190-year-old storm wiggles like gelatin and shape-shifts like a squeezed stress ball.

The unexpected observations, which Hubble took over 90 days from December to March, show that the Great Red Spot isn’t as stable as it appears, according to astronomers.

The Great Red Spot, or GRS, is an anticyclone, or a large circulation of winds in Jupiter’s atmosphere that rotates around a central area of high pressure along the planet’s southern midlatitude cloud belt. And the long-lived storm is so large — the biggest in the solar system — that Earth could fit inside it.

Although storms are generally considered unstable, the Great Red Spot has persisted for nearly two centuries. But the observed changes in the storm appear related to its motion and size.

A time lapse of the images shows the vortex “jiggling” like gelatin and expanding and contracting over time.

Researchers described the observation in an analysis published in The Planetary Science Journal and presented Wednesday at the 56th annual meeting of the American Astronomical Society’s Division for Planetary Sciences in Boise, Idaho.

“While we knew its motion varies slightly in its longitude, we didn’t expect to see the size oscillate as well. As far as we know, it’s not been identified before,” said lead study author Amy Simon, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, in a statement.

“This is really the first time we’ve had the proper imaging cadence of the GRS,” Simon said. “With Hubble’s high resolution we can say that the GRS is definitively squeezing in and out at the same time as it moves faster and slower. That was very unexpected.”

A shifting extraterrestrial storm

Astronomers have observed the iconic crimson feature for at least 150 years, and sometimes, the observations result in surprises, including the latest revelation that the storm’s oval shape can change dimensions and look skinnier or fatter at times.

Recently, a separate team of astronomers peered into the heart of the Great Red Spot using the James Webb Space Telescope to capture new details in infrared light. The Hubble observations were made in visible and ultraviolet light.

The study, published September 27 in the Journal of Geophysical Research: Planets, revealed that the Great Red Spot is cold in the center, which causes ammonia and water to condense inside the vortex and create thick clouds. The research team also detected the gas phosphine within the storm, which could play “a role in generating those mysterious” red colors that make the Great Red Spot so iconic, said study coauthor Leigh Fletcher, a professor of planetary science at the UK’s University of Leicester, in a statement.

NASA scientists use Hubble’s sharp eye to track the storm’s behavior once a year through the Outer Planet Atmospheres Legacy, or OPAL, program, which Simon leads. Scientists use this program to observe the outer planets in our solar system and watch how they change over time.

But the new observations were taken separately through a program dedicated to studying the Great Red Spot in more detail by watching how the storm changed over a matter of months, rather than a singular, yearly snapshot.

“To the untrained eye, Jupiter’s striped clouds and famous red storm might appear to be static, stable, and long-lived over many years,” Fletcher said. “But closer inspection shows incredible variability, with chaotic weather patterns just as complex as anything we have here on Earth. Planetary scientists have been striving for years to see patterns in this variation, anything that might give us a handle on the physics underpinning this complex system.”

Fletcher was not involved with the new study.

The insights gathered through the program’s observations of the largest storms in our solar system can help scientists understand what weather may be like on exoplanets orbiting other stars. That knowledge can broaden their understanding of meteorological processes beyond ones we experience on Earth.

Simon’s team used Hubble’s high-resolution images to take a detailed look at the size, shape and color changes of the Great Red Spot.

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

The changes included a brightening of the storm’s core when the Great Red Spot is at its largest size as it oscillates.

“As it accelerates and decelerates, the GRS is pushing against the windy jet streams to the north and south of it,” said study coauthor Mike Wong, planetary scientist at the University of California, Berkeley, in a statement. “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.”

On Neptune, dark spots can drift across the planet since no strong jet streams are holding them in place, Wong said, while the Great Red Spot is trapped between jet streams at a southern latitude on Jupiter.

A shrinking spot

Astronomers have noticed the Great Red Spot shrinking since the OPAL program began a decade ago and predict that it will continue to shrink until it reaches a stable, less-elongated shape, which could reduce the wobble.

“Right now it’s over-filling its latitude band relative to the wind field. Once it shrinks inside that band the winds will really be holding it in place,” Simon said.

The new Hubble study fills in more pieces of the puzzle about the Great Red Spot, Fletcher said. While scientists have known that the westward drift of the storm has an unexplained 90-day oscillation, the accelerating and decelerating pattern doesn’t seem to change although the storm is shrinking, he said.

“By watching the GRS over a few months, Hubble has shown that the anticyclone itself is changing its shape along with this oscillation,” Fletcher said. “The shape change is important, as it may be affecting how the edge of the vortex interacts with other passing storms. Besides the gorgeous Hubble imagery, this study shows the power of observing atmospheric systems over long periods of time. You need that sort of monitoring to spot these patterns, and it’s clear that the longer you watch, the more structure you see in the chaotic weather.”

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