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Seeing red

发布时间:2019-03-07 05:17:01来源:未知点击:

By Robert Adler JUPITER’S Great Red Spot resembles a lopsided wedding cake, say astronomers who have worked out the most detailed models so far of the planet’s atmosphere. Infrared spectra from the Galileo spacecraft allowed Kevin Baines, a planetary scientist at NASA’s Jet Propulsion Laboratory in California, and his colleagues to peer into the giant planet’s complex atmospheric stew. They found that the Great Red Spot, a hurricane-like storm system twice the diameter of Earth and at least 300 years old, is capped by a tilted tower of ammonia clouds about 20 kilometres tall. As he will tell a meeting of the American Astronomical Society in Padua, Italy, in October, these clouds form a raised oval about two-thirds the diameter of the base. “It looks like a wedding cake,” Baines says. Spirals of clouds extend out across the top of the upper tier, and deeper layers can be glimpsed through clearings. Fred Taylor, a physicist at Oxford University, thinks the spiral helps explain how the Red Spot works. “It would have a relatively small region below it of rapidly rising gas rich in water, ammonia and other quite exotic things,” he says. “At a certain height, they spread out, like the cap of a terrestrial hurricane.” Baines thinks the upwelling acts like a rock in the middle of a stream. “You get a bow wave where the east side gets lifted up,” he says. “Then the clouds descend as the core rotates.” Taylor, Baines and others have pieced together tentative models of the upper layers of Jupiter’s atmosphere—from a high, thin hydrocarbon haze, through layers of ammonia and hydrogen sulphide clouds, down to clouds of water vapour at six times the pressure of Earth’s atmosphere. The Cassini probe is expected to transmit even sharper images when it passes Jupiter next year. These may help answer questions such as what makes the spot red, and why it has lasted so long. “Their work is one piece of the puzzle,” says Andrew Ingersoll, a planetary scientist at the California Institute of Technology,