The gas-giant planets rotate quickly and have extremely fast winds in the upper layers of their huge atmospheric clouds. Saturn has the fastest winds, more than twice as fast as Jupiter.

Saturn rotates tremendously fast. At its equator, Saturn rotates in 10 hours and 14 minutes. That’s more than twice as fast as Earth rotates! Scientists measure Saturn’s rotation rate by monitoring radio waves generated by Saturn’s interior. The radio waves oscillate, or wave, in a pattern that is analyzed and calculated to determine its rotation speed. Saturn’s giant magnetosphere makes one complete turn in the same period of time, verifying the speed of rotation. Saturn’s magnet field creates its magnetosphere, which is generated by the layer of liquid hydrogen under Saturn’s dense cloud layer.

The atmospheric wind speed of a planet is measured by tracking visible cloud features in the atmosphere and measuring their speed to the planet’s internal rotation rate of radio waves. When the Voyager spacecraft flew past Saturn in 1980 and 1981, the wind speeds at Saturn’s equator were about 1,100 miles per hour faster than the internal rotational period. Recent observations using the Hubble Space Telescope measured Saturn’s fastest equatorial winds at only 690 miles per hour. Scientists don’t know why the wind speeds have slowed so much. The Cassini spacecraft, now at Saturn, may provide new information to understand the dramatic change.

Jupiter’s internal rotation rate is about 10 hours. The winds on Jupiter are usually about 335 miles per hour faster than the rotation rate. Uranus and Neptune are more complex and harder to calculate atmospheric wind speeds. Their magnetic fields are at an angle compared to their rotational axes. Uranus is tilted at 60 degrees and Neptune is tilted at 47 degrees.