November 14, 2013
Mystery On Jupiter: The Great Red Spot
[ Watch the Video: The Mystery Behind Jupiter's Long-lived Storm ]
Brett Smith for redOrbit.com – Your Universe Online
A new model being presented at the 66th Annual Division of Fluid Dynamics Meeting in Pittsburgh next week provides a possible explanation for why the turbulent red vortex has lasted so long.
"Based on current theories, the Great Red Spot should have disappeared after several decades. Instead, it has been there for hundreds of years," said study researcher Pedram Hassanzadeh, who is a post-doctoral planetary scientist at Harvard University.
There are many forces working against the Red Spot that the study team had to consider. Turbulence in and around the Red Spot can draw energy out of its winds. Two strong jet streams that pass the spot in opposite directions can reduce its rotational momentum. The vortex also loses energy by radiating heat.
One fluid dynamics theory says that a large vortex can survive for an extended period of time if it absorbs smaller, nearby vortices.
However, study researcher Philip Marcus, a professor of fluid dynamics at the University of California, Berkeley said, “This does not happen often enough to explain the Red Spot's longevity.”
To investigate this mystery, Hassanzadeh and Marcus developed a model that differed from other models by being completely three dimensional in nature and having a very high resolution.
"In the past, researchers either ignored the vertical flow because they thought it was not important, or they used simpler equations because it was so difficult to model," Hassanzadeh explained.
However, the study team found vertical factors are the key to the Great Red Spot's longevity. As the vortex expends energy, a vertical stream sends hot gases from above and cold gases from below into the vortex, restoring some of its lost energy.
The team’s model also predicts winds from the high-speed jet streams being drawn into the vortex, bringing in additional energy.
The researchers said the same vertical forces could explain why oceanic whirlpools, like those formed near the Straits of Gibraltar, can last for years. According to prevailing theories, vortices also play a role in the formation of stars and planets by pulling in interstellar dust and rocks into large masses.
While the study model being presented does not completely explain the Red Spot's longevity, the study team said the occasional assimilation of smaller vortices might supply the extra energy needed to extend the life of such a turbulent phenomenon. The study team noted they have begun to make adjustment to their computer model to test this theory.
Gian Domenico Cassini is thought to have given the earliest known description of the spot, sometime between 1665 and 1713. The spot is big enough to hold two or three planets the size of Earth. In early 2004, the Great Red Spot had about half the longitudinal extent it had a century ago. Some calculations say the spot could become circular by 2040. However, this is unlikely due to the distortive effect of the nearby jet.