Why Jupiter's Red Spot Won't Die
Jupiter’s signature Great Red Spot is sort of the Doctor Who of storms: It just won’t die — even when it has been proven that it must die. And now, for the first time, some fluid dynamicists have finally hit on some of the secrets to the giant storm’s longevity.
“It’s the largest, most enduring storm in the solar system,” said Philip Marcus of University of California, Berkeley, in a presentation at the meeting of the American Physical Society’s fluid dynamics division in Pittsburgh on Monday.
The Red Spot is about 24,000 km across, east to west, 12,000 km from north to south, and a mere 40 km deep. Its wind are roaring around at about 225 miles per hour and this incredible monster has been observed from Earth almost continuously for at least 150 years, he said. But based on all the modeling that’s been done to try and explain the Red Spot, it just isn’t possible.
“It should have disappeared in about four years according to the models,” Marcus said. “So there’s a problem. How do you go from four years to 150 years?”
One of the possibilities that was explored is that the Red Spot gets its energy from eating up smaller vortices, which it has been observed to do on occasion. But the math on that doesn’t add up to enough to support the giant storm, Marcus said.
So what he and his colleague Pedram Hassanzadeh of Harvard University did was build a better model. Previous models ignored the third, vertical dimension of the storm because it is so tiny compared to the width and breadth (plus, it was easier to model that way). As a result, the earlier works had all treated the Red Spot as a flat, 2-dimensional phenomenon.
When Marcus and Hassanzadeh factored in the interactions of the thin storm with the layers of atmosphere below it, the sphericity of Jupiter, and the changing densities of the gases at different levels in the atmosphere, the modeled lifespan of the storm jumped dramatically. The secret source of power for the storm is energy that is moving vertically, not horizontally.
“What we found is that the spot can last 800 years,” said Hassanzadeh. The 150 years on record for the Red Spot is just a minimum, he explained.
The discovery of the causes of the Red Spot’s longevity could also help explain some other natural vortices that also last far longer they they ought to, said Marcus. One of them is large, long-lived oceanic eddies, he said. Another are what are called “zombie vortices” that play a role in the formation of stars and planets.
IMAGE: An iconic view of Jupiter’s Great Red Spot as seen by the Voyager 1 spacecraft in 1979. Credit: NASA