Red Spot Offers Window Into Jupiter

Jan. 14, 2008 -- The mysterious Great Red Spot of Jupiter may be providing an opportunity to see how the giant planet works, say researchers.

Spacecraft observations of the way bands of high winds scream past the Red Spot show how the spot -- inaccurately described as a storm -- is actually far calmer than other parts of the Jovian atmosphere.

"The Red Spot is very quiet at its center," said Jupiter researcher Philip Marcus of the University of California at Berkeley.

The winds at the center are just 9 or 10 miles per hour, whereas around the perimeter they exceed 200 miles per hour.

Numerical modeling of the spot, as well as laboratory experiments trying to reproduce the dynamics of the Great Red Spot indicate there's more going on than meets the eye.

"One of the interesting things we've discovered about this is that when you try to recreate this in the lab, it's highly, highly unstable," Marcus told Discovery News. "It just literally rips itself to shreds."

Yet the real Giant Red Spot is one of the most stable features visible on Jupiter. So what gives?

"It's telling us something about Jupiter," said Marcus. "There must be something special about Jupiter's atmosphere that makes it different."

Marcus and his colleagues have published a paper on some of their insights into what the spot is telling us about Jupiter in a paper published in the December issue of the Journal of Atmospheric Sciences.

One thing that stands out about Jupiter's atmosphere is that it has a zig-zag pattern of twelve jet streams which make up its signature pastel-toned bands. Earth, by comparison, has only two jet streams. The Great Red Spot is sandwiched between two of these jets streams, forcing the winds that power those perimeter winds to deflect around the spot.

The location of the Red spot near the equator and the highest speed jet streams suggests that there is some critical speed at which the spot becomes a stable arrangement in the atmosphere.

Marcus compares it to the angle of the face of a sand dune -- the sand can pile up pretty steeply, but at some point the sand will become unstable and cascade. So the dune face maintains a tilt just short of the critical point.