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STORMY ENCOUNTER. Image taken Dec. 21, 2001, shows Jupiter’s Great Red Spot and the nearby, smaller oval storm (arrow) in the planet’s southern hemisphere.Ed Grafton

Amateur and professional sky watchers are pointing their telescopes at Jupiter this month to record what could be a historic encounter. Two huge storms on the giant planet are beginning to encounter each other, and no one knows what will happen as these titans meet.

The more prominent of the swirling storms, Jupiter’s Great Red Spot, is twice as wide as Earth. It has endured for more than 300 years. The other storm, about one-third as wide, has persisted in an adjacent band of clouds since the 1930s. The Great Red Spot encounters storms in this band about once every 2 years. The current interaction is different from earlier ones because what had been three oval storms have merged into one (SN: 11/18/00, p. 328).

Although this oval doesn’t appear larger than any of the earlier trio, it may be more massive. If so, the current encounter with the Great Red Spot could be dramatic, notes planetary scientist Reta F. Beebe of New Mexico State University in Las Cruces. For instance, the oval could be torn apart or stalled as it approaches the edge of the larger storm. It may even give up some of its own stuff—fresh ammonia ice crystals—to the Great Red Spot, endowing it with a white fringe.

The two storms are approaching each other at 30 kilometers per hour, with the white oval passing just south of the Great Red Spot. The large wind speeds, up to 700 km per hour, at the fringes of both of these hurricane-like storms sets the stage for an extraordinary interaction, says Amy A. Simon-Miller of NASA’s Goddard Space Flight Center in Greenbelt, Md.

Aside from testing the stability of the oval, the encounter could reveal how much water lies beneath the storms. The greater the amount of water, the larger the separation at which the two storms can begin to interact, notes Andrew P. Ingersoll of the California Institute of Technology in Pasadena.

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