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The atmosphere of Saturn is 96 percent hydrogen and three percent helium. The upper clouds in Saturn's atmosphere are of ammonia the lower layer clouds are composed of ammonium hydrosulfide or water. Saturn is to be the solar system's windiest planet. Winds near the equator are thought to blow in excess of 1,100 miles per hour, four times the fastest winds ever on Earth. Like Jupiter, Saturn often shows signs of storm activity. It is the only planet in the solar system known to have a polar vortex. A polar vortex is a cyclone-like storm near a planet's polar region(s). The temperature in Saturn's polar vortex is about 65 degrees warmer than the average temperature on Saturn. In 2006, a NASA spacecraft the of a hurricane-like storm in Saturn's southern pole. The storm was because of its visible eyewall. Previous to this discovery, eyewalls had only been in hurricanes on Earth.