A Planet's Spots

As every astronomer knows, Jupiter has spots. They are believed to be disturbances in the planet's atmosphere, which is many thousands of miles thick and is made up of such unpleasant gases as methane and ammonia. At a Manhattan meeting of the American Meteorological Society, Dr. Yale Mintz of the University of California proposed a theory to account for one kind of Jovian spot.

Dr. Mintz thinks that the light & dark spots, each of which stretches thousands of miles across the face of Jupiter, near its equator, are analogous to the tropical storms that have recently been discovered in the earth's high atmosphere. The earth storms are masses of cold air that form just north of the equator, and probably to the south of it, too, at 30,000 ft. With each air-mass goes a sheet of high white cloud as much as 1,200 miles across. To a Jovian amateur astronomer, the clouds would look like brightly shining spots framing the earth's equator.

The earth's storms are connected in some way with changes in the sun's radiation. They develop just after the sun's surface shows "calcium flocculi": a nubbly appearance that signals an unusually large output of ultraviolet light. Shortly after the sun gets nubbly, the high white clouds show up.

Dr. Mintz collected records of Jupiter's spottedness and made charts to show its variation over the years. Then he did the same for variations in the sun's flocculi. The two curves matched strikingly. After nearly every burst of ultraviolet from the sun, Jupiter broke out in spots.

No one is quite sure why ultraviolet light has these effects. Since Jupiter's atmosphere is not like the earth's, its spots may be formed in a somewhat different way. Dr. Mintz suspects that Jupiter's white spots may be clouds of ammonia crystals floating high, like the cirrus clouds in the earth's atmosphere. Its dark spots may be places where the Jovian atmosphere is unusually clear.

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