I have been intrigued by the Great Red Spot since 1979, when I viewed the Voyager images only days after NASA processed them. The beautiful structure of this extraordinary atmospheric intrigued me since my career was evolving from astrophysics to fluid dynamics – the study of how liquids and gases move. What better way to begin exploring the fundamental physics and math of fluid dynamics than to study the Great Red Spot?

Jupiter’s clouds and vortices

I believe that the Great Red Spot is in no danger of disappearing. By analyzing the cloud images with computer models that incorporate the physics of how fluids move, my research group at Berkeley was able to determine the area of the spot. We discovered that the area of the spot cloud is larger than its underlying vortex, the swirling gas that defines it. The question then becomes: Does a decrease in the area of the cloud mean that the vortex itself is shrinking?

It is difficult to determine the relationship between the cloud’s size and the vortex’s size or even how Jovian clouds form and dissipate. Therefore, to understand the health of the spot, planetary scientists need to study the health of its vortex and not its cloud; the cloud’s shrinkage is not a harbinger of death. Based on the spot’s interactions with other vortices my Berkeley group found there is no evidence that that vortex itself has changed its size or intensity.

Jupiter’s atmosphere contains vortices besides the Great Red Spot, some of which are useful for monitoring its health. Some, like this spot, are anticyclones that rotate in the opposite direction of the planet’s spin; others are cyclones that rotate in the same direction as the planet’s spin. Anticyclones appear as bright clouds and so are easily detectable, but cyclones (except at the poles) often have filamentary clouds or no clouds at all.

How do we know that Jovian cyclones exist when clouds are not visible? For more than a century astronomers documented the motions of cloud-covered anticyclones as they slowly drifted across Jupiter. Changes in their speeds were often abrupt and seemed to occur for no reason. However, by assuming that these observable vortices interact with cloud-free (and unobservable) cyclones, we can explain the abrupt changes.