Saturn has a reputation as one of the windiest planets, with broad swaths of gales encircling the planet and traveling in alternating directions. Agustin Snchez-Lavega of the Universidad del Pais Vasco in Spain and his colleagues studied the behavior of these so-called equatorial jet winds using data collected by the Hubble Space Telescope between 1996 and 2002 and by Voyager in the early 1980s. They found that the jets around the planet's middle had slowed down significantly, from about 1,700 kilometers an hour to 1,000 kilometers an hour. The speeds of winds near the planet's poles, in contrast, stayed relatively stable over the same time period.
The scientists suggest that the slowdown may be the result of seasonal change or shadows cast by the gas giant's rings. The changing orientation of the planet with respect to the sun prevents large sections of it from receiving radiation for long periods, and differential heating (and the resulting differences in pressure) creates wind. Astronomers should have further opportunities to probe the cause when NASA's Cassini spacecraft reaches the planet next year.