Explaining a Jovian Mystery

Ever since they discovered it three centuries ago, astronomers have been baffled by Jupiter's Great Red Spot. The larger-than-earth-sized blemish, which drifts mysteriously across the face of the solar system's biggest planet, sometimes covers an area 8,000 miles wide and 30,000 miles long. Occasionally it grows noticeably brighter; at other times it almost vanishes. Other than to speculate that the spot is caused by an unusual deviation in the planet's magnetic field or a physical irregularity somewhere below its atmosphere, scientists have long been at a loss to explain either the nature of the spot or its odd behavior. Now they have offered a new theory that seems to go far toward solving the Jovian enigma.

Writing in the planetary-science journal Icarus, Scientists William Streett, Harry Ringermacher and George Veronis contend that the Red Spot is caused by a huge solid chunk of hydrogen afloat in a sea of gases in Jupiter's atmosphere. How could a solid float in gases? The authors explain that the phenomenon becomes possible when certain mixtures of gases are subjected to high enough pressures. As one of the gases in the mix becomes liquefied and then begins to solidify under increasing pressure, a peculiar reversal takes place: the solidifying mass--like water turning into ice--becomes lighter and less dense, capable of floating in the surrounding mixture of liquids and gases.

Indirect Evidence. To substantiate his hunch that this is what happens on Jupiter, Lieut. Colonel Streett (a mechanical-engineer-turned-physicist who heads West Point's new science research laboratory) calculated the effects of high pressures on hydrogen and helium, the basic gases in the Jovian atmosphere. He deduced that if such a combination were subjected to several hundred thousand times earthly atmospheric pressure (14.7 Ibs. per sq. in. at sea level), the hydrogen would begin to solidify first, its density becoming less than that of the remaining gaseous mixture of hydrogen and helium. Physicist Ringermacher, then a Private First Class stationed at West Point, and Yale Geophysicist Veronis confirmed that such pressures could well exist at a depth of several thousand miles in Jupiter's atmosphere.

While an earthbound observer could not see such a deeply submerged island of hydrogen, the three men concluded, he probably could detect some indirect evidence of its existence. Because the huge mass would act as a barrier against the hot, rising currents characteristic of the Jovian atmosphere, the area above the solidified hydrogen would be relatively calm and free of the white ammonia clouds that cover much of the planet. As a result, the observer would be able to see much farther into the atmosphere and perceive the deep red at its lower depths.

Disturbing Currents. Furthermore, if anything disturbed the buoyancy of the floating hydrogen mass--atmospheric currents, for example--it might begin to sink. That would enlarge the area of the protected zone and make the Red Spot appear even bigger. If something made the solid rise, however, the spot would grow smaller. In fact, pieces of solid hydrogen could begin to break off (as a result of the reduced pressure at the higher elevations), and heat trapped under the hydrogen mass might bubble up. As it escaped, enough clouds would eventually be formed in the upper atmosphere to obscure the Red Spot. Not for long, though. As soon as the disturbing atmospheric currents diminished, the remaining solid hydrogen would begin to sink again. As it dropped to levels of higher pressure, more solid material would be formed; the hydrogen mass would grow, returning the Red Spot to its old prominence.

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