Science / Medicine : Jupiter's Great Red Spot Waning

From Times staff and wire reports

Jupiter's Great Red Spot may soon lose some of its red coloring because of a weather change on the largest planet in the solar system, NASA astronomers said last week.

A 6,200-mile-wide belt of clouds on the planet is starting to change to its typical dark brown smoggy color, 13 1/2 months after it turned white, astronomers said. When this happens, eddies in its winds start feeding ammonia ice crystals into the spot, washing out some of the red color. The cloud belt sits just north of the Great Red Spot.

If history repeats itself, the Great Red Spot--a hurricane system almost twice the size of Earth--soon should become less red. The cloud belt turns brown when violent storms mix Jupiter's atmospheric gases, allowing sunlight to trigger reactions by the ammonia and natural gas, or methane. That creates brownish photochemical smog that drifts down in the planet's atmosphere.

When the cloud belt turns white, the eddies diminish, reducing the amount of ice entering the Great Red Spot and allowing it to turn darker red.

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