Jupiter's Red Spot is Shrinking

By Larry O'Hanlon, Discovery News

Jan. 4 — Jupiter's giant Red Spot is shrinking, says a NASA researcher.

The most recognizable feature on our solar system's biggest planet has been changing shape and getting smaller, said Amy Simon-Miller, an astrophysicist at NASA's Goddard Space Flight Center.
Her study of the shrinking red spot will appear in a future edition of the journal Icarus and is summarized in Sky & Telescope magazine.

There is even a chance that the Red Spot could disappear altogether. "It's a distinct possibility," said Simon-Miller.

The trouble is, she said, no one can say for certain because no one is sure how the Red Spot — an Earth-sized gaseous whirlpool — was created or how it maintains itself.

Simon-Miller discovered the changes in the Red Spot's size by comparing modern spacecraft images of Jupiter with data on the red spot gathered by astronomers as far back as the 1880s. The 19th-century data suggest that the spot was once more than three times wider in the east-west direction than it is today.

The oblong, sausage-like shape came from the fact that the spot exists in a band of Jupiter's atmosphere that's sandwiched between two roaring jet streams, so there's no room for expansion in the north-south direction.

"It's kind of like a ball bearing between two sheets of metal (moving in opposite directions)," said planetary scientist Andrew Ingersoll of the California Institute of Technology.

Although the shrinking of the Red Spot may herald its eventual demise, agreed Ingersoll, there's also a chance that it might stabilize and survive on a steady diet of small white spots, something the Red Spot has shown an appetite for in images taken by the Galileo and Cassini spacecrafts.

Eating smaller spots that are rotating in the same direction as the Red Spot provides an energy boost that seems to work in computer models of the Red Spot, said Ingersoll. The same models indicate that the Red Spot itself is a very stable feature that wouldn't need a large diet of smaller spots to keep going, he said.

Even if you take the little spots into account, however, there are still a lot of unanswered questions, said Ingersoll, since no one knows what causes the smaller spots either.

For that matter, just what makes the spots red and white is still a complete mystery. Ingersoll hopes that still unanalyzed data gathered by the Cassini spacecraft when it swung past Jupiter en route to Saturn may someday provide answers.