Jupiter’s Great Red Spot Is Behaving Strangely

For a time, it looked as though the planet’s defining feature might be on the verge of extinction.

Jupiter's Great Red Spot

If on a clear and starry night in mid-May you had trained a high-powered telescope on just the right part of Jupiter, you would have seen something very, very strange. The Great Red Spot, one of our solar system’s most famous features, would have appeared to be slowly unraveling. You would have seen the swirling storm system casting off ribbons of rose-colored gas like petals in the wind. It would have been beautiful.

Earlier this year, dozens of die-hard amateur astronomers across the globe began noticing that the Great Red Spot’s ordinarily ovoid figure looked distorted. By April, it seemed to be shedding red flakes. In May, that flaking grew so extreme that the spot looked as though it might disintegrate.

The amateur community, a tight-knit group that regularly communicates and shares photos over social media, was charged with excitement and anxiety. It had never seen anything like this before, and members worried what it might mean. On a warm Australian night in early May, the longtime amateur and software engineer Anthony Wesley was floored when his telescope captured an image of a bright streamer curling away from the spot. That, he thought, is not something you see every day.

Humans have been observing the Great Red Spot since the invention of the telescope in the 1600s, and at its peak, the storm was three times wider than the Earth. Since the late 19th century, though, it has been shrinking, slowly but steadily. In 2012, amateur astronomers noticed that its diminution had accelerated. And in May, when they saw it flaking, they feared that it might be on the verge of extinction.

“Are we seeing the ‘beginning of the end’? The GRS Death dance?” one astronomer wondered aloud in a Facebook group for Jupiter enthusiasts. “I was scared because if the Great Red Spot disappears … it’s like you go to New York and remove the Statue of Liberty,” another told me.

As it has shrunk, the storm has also grown darker, redder, and taller; this year, the color palette is more intense than ever, according to a NASA press release accompanying new photos of Jupiter taken by the Hubble Space Telescope. Through all those changes, though, the spot’s position has never shifted: Twin jet streams circle the planet in opposite directions and lock the storm in place. Moving at speeds approaching 400 miles an hour, the jets constantly bombard the spot with clouds and vortices; some incorporate themselves into its body, while others pass through unhindered. The whole system looks something like a wristwatch wrapped around the planet, with the jet streams for a band and the spot for a face.

In the months after they first recognized the spot’s unusual behavior, the amateurs around the world monitored it at virtually all hours of the day and sent their images to the scientists at NASA’s Outer Planet Atmospheres Legacy program. The storm looked to have undergone a sudden contraction (though more recent amateur data suggest it has since returned to its former size). But when the scientists analyzed its behavior using the amateur images along with the higher-resolution Hubble photos, they arrived at a very different story.

The Great Red Spot was not dying—at least not any faster than it had been before. To the amateurs, it had looked as though strands of the storm were tearing away. But according to Amy Simon, who leads the Outer Planet program, that impression resulted from the fundamental imprecision of visual measurements.

Recently, Simon told me, the program has started measuring the storm using its dynamics instead of its visual features. Tracking the storm’s velocity rather than its color revealed that much of the red gas that had seemed to be flowing out of the Great Red Spot was actually flowing in. This, she said, is nothing new.

“It’s always doing this,” Simon told me. The Great Red Spot “is always pulling stuff in and parts of it are flying off. That is not unusual at all.” The difference this time, she said, has to do with both the appearance and the behavior of those mysterious red flakes.

For starters, the material flowing into and around the red spot has taken on a reddish color more like the storm’s, creating the illusion of shedding. Simon told me that shift in color occurs before the material ever reaches the storm, while Glenn Orton, a scientist at the NASA Jet Propulsion Laboratory, thinks the shift happens later.

Either way, the material’s unusual movements have only enhanced the illusion. Typically, Simon explained, material from the jet streams either integrates into the storm or passes clean through. In recent months, though, it has been noncommittal at times, circling the periphery of the storm a few times before escaping its orbit, as though going for a quick carousel ride. That outer circuit, Orton says, has “gone from a two-lane country road … to a six-lane highway.” The ribbons of gas torn from the storm may never really have been part of it at all, more commuters than inhabitants.

Taken together, these findings offer a clear answer to the mystery of why the Great Red Spot is disintegrating: It isn’t. But with that simple answer comes a new mystery just as perplexing as the first: If it wasn’t disintegrating, why did it look like it was? As is often the case with the workings of the Great Red Spot, scientists don’t yet have an explanation.

For now, Simon told me, they must simply accept much of Jupiter’s behavior as random. By investigating the recent changes, though, some scientists hope to find clues to perhaps the planet’s greatest mystery of all: why the Great Red Spot is red in the first place.

Tim Dowling, an atmospheric-physics professor at the University of Louisville, views the recent disruptions as a chance to test scientific models explaining the spot’s color. Many of its observers have hypothesized that it may grow redder at higher altitudes, but the specific mechanics of what is turning red and how remain open to interpretation. Simon sees a few possible explanations. Dowling favors the crème brûlée model, so called because it posits that the spot’s color comes from a thin coating of solid particles atop a bed of clouds, just as the burnt crust of a crème brûlée sits atop the custard.

When I asked Anthony Wesley about Simon’s account of the Great Red Spot’s behavior, he was skeptical, though he freely acknowledged that, given the ambiguity, I might be better off taking Simon and her colleagues at their word. And yet he knew what he had seen with his own eyes—parts of the spot spinning out and away. Wesley’s way of looking at the cosmos is distinct from NASA’s, and the discrepancy in their accounts reflects that. Judging by the velocities Simon measured in her data, the storm system isn’t contracting any faster than it has been in recent years. And judging by the images Wesley and the other amateurs captured, the red oval we see when we look up at Jupiter through a telescope shrank considerably before returning to its former size.

If, somehow, the Great Red Spot faded from view but the storm spun on, would it still be the Great Red Spot? The underlying system, in Simon’s words, would be the same. But if Wesley awoke in the middle of the night to find that the cosmic phenomenon he’d spent more than 15 years photographing had vanished from sight, that fact might come as little consolation.