Re: what is the composition of the great red spot on the planet Jupiter?

The short answer is, nobody really knows.

We do know that Jupiter is made up mostly of hydrogen and helium, with traces of other elements. Colors in the clouds are likely to be products of photochemistry involving the "trace elements," which include sulfur and phosphorus -- both of which form compounds which have colors similar to those seen in the Jovian atmosphere. (Now there's a misnomer; Jupiter is essentially all atmosphere!)

The Great Red Spot is a storm which has been whirling continuously for centuries. Probably there is an upwelling of colored molecules from lower parts of Jupiter, which give the Spot its color. What those molecules are, no one knows.

Not too much is known for certain about the chemistry of Jupiter, and what we've found out recently -- in particular from the Galileo Probe, but also from observations of the crash of Comet Shoemaker-Levy 9 -- tended to demolish a lot of what we thought we knew. With luck, we'll be able to get more information as we process data from the Galileo Orbiter.

                         Dan Berger
                         Bluffton College
                         http://cs.bluffton.edu/~berger/