Observations from the 1800s indicated that Jupiter's spot was once more than four times the diameter of Earth.
Jupiter isn't losing its most famous feature anytime soon.
The planet's Great Red Spot — which appears as a prominent, flame-hued blemish on the gas giant — is a massive storm that has been churning on Jupiter for centuries. Despite observations over the past decade that suggest the storm's clouds are shrinking, researchers at the University of California, Berkeley, who have been studying the storm's behavior with computer simulations now say there is no evidence that the megastorm is dying.
"I would take all of that with a grain of salt," said Philip Marcus, a professor of mechanical engineering at Berkeley. "We feel confident that the sky is not falling."
Marcus and his colleagues presented their research Monday at the 72nd annual meeting of the American Physical Society's Division of Fluid Dynamics in Seattle.
The Great Red Spot's outlook was called into question after images from May and June showed huge red "flakes" sloughing off the storm. A 2018 NASA study also found that the megastorm, which currently measures more than 10,000 miles wide, has contracted since 1878, when continuous observations of the spot began.
Observations from the 1800s indicated that Jupiter's Great Red Spot was once more than four times the diameter of Earth, but now, the storm is just big enough to fit a little more than one Earth inside it, according to NASA. This prompted some scientists to wonder if the Great Red Spot was on the verge of disappearing.
But Marcus said changes in the dynamics of the storm's clouds likely betray the strength of the underlying vortex.
"I was skeptical that measuring clouds tells you about the underlying engine or vortex," he said. "If one were to study climate change on Earth, you want to take a look at the clouds because they're indicating something, but there's a lot more going on than what's in the clouds."
Though the storm's appearance has changed in the past decade, particularly in the movement of the spot's clouds, the researchers found no evidence that the underlying vortex's size or intensity has changed.
Marcus added that the flaking observed earlier this year by amateur astronomers can be explained by regular weather phenomena on the planet.
The Great Red Spot is known as an anticyclone, because the storm's winds swirl around a center of high atmospheric pressure that makes it rotate opposite to how hurricanes churn on Earth.
Marcus said the flakes that were seen peeling off the storm in the spring coincided with observations of the Great Red Spot merging with what were likely small anticyclones as well as a separate incident where the megastorm repelled and deflected a nearby cyclone.
As such, the flakes may have been "undigested lumps of merged anticyclones," he said.
It's thought that anticyclones merge with each other on Jupiter every few months, and close encounters between anticyclones and cyclones occur once every few years. Marcus said it's not common for these two events to occur at the same time, but maintained that when he and his team conducted simulations of these two events simultaneously, they were able to recreate the conditions on Jupiter.
Gordon Bjoraker, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, was not involved with the new research but agreed that it's unlikely that Jupiter's defining feature is facing any imminent threats.
The Great Red Spot is sometimes likened to a wedding cake, and Bjoraker, who has conducted extensive research on Jupiter's atmosphere, said images taken by amateur astronomers and the Hubble Space Telescope capture only the top and center layers.
"The Great Red Spot is massively thick," he said. "There are changes to the top of the cake, but the base is still huge."
And unlike shorter-lived storms on other planets, such as Neptune, wind currents on Jupiter keep the Great Red Spot drifting east to west, rather than pushing it north or south, where polar or equatorial wind jets could tear the storm apart.
"If it doesn't wander north or south, it's not going to disappear," Bjoraker said. "It's remarkably stable."