THE SURFACE OF JUPITER

J upiter is thought to have formed by a the gravitational collapse of the primitive solar nebula. Dust particles condensed as the nebula cooled and coalesced into Jupiter's rocky core as a result. This rocky core became large enough that it pulled together surrounding gases from the nebula and eventually formed a planet. This is supported by Jupiter's make-up which is mostly hydrogen and helium. Since the climate of Jupiter is fairly warm no solid surface exists, instead there is only a gradual transition to liquid. About one-fourth of the way toward the center of the planet, the pressure and temperature are so high that the liquid becomes metallic (that is, the molecules are stripped of their outer electrons).

R otation and currents within the metallic hydrogen interior of Jupiter generate a magnetic field, much like the molten core of Earth does. Jupiter's magnetic field is very unique and changes as the planet rotates.

J upiter's atmosphere also contains trace amounts of water, ammonia, methane, and other organic (carbon) compounds. Astronomers theorize that three layers of clouds exist, separated by about 30 km (19 miles) in altitude. The lowest are made of water ice or droplets, the next are crystals of a compound of ammonia and hydrogen sulfide, and the highest are ammonia ice. Of the observed clouds, the blue ones are warmest and therefore at the lowest altitude. Browns, whites, and reds lie increasingly higher, in that order. These shades are believed to be caused by chemical disequilibrium, which allows sulfur, phosphorus, and organic compounds to color the clouds. This disequilibrium may be due to impact by charged particles, rapid vertical motion through changing temperature levels, or lightning.

T he winds on Jupiter move in jets parallel to the equator. Weather on Jupiter is still not well understood. Eddies and storms form and dissipate, some lasting only a few days, others much longer. Some get caught between regions of different wind speeds and are ripped apart. Larger eddies, such as long-lived white spots and the Earth-size Great Red Spot, are able to survive by rolling like ball bearings between zones.