Saturn, one of the windiest planets, has experienced an unexpected and dramatic change in its weather over the past 20 years or so.

Since the Voyager flybys of 1980-81, the windspeed in its equatorial regions has declined by about 40%, from 1,700 km to 1,000 km per hour. The change is probably explained by Saturn's seasonal cycle of 29.4 years (the length of time it takes to orbit the Sun), as well as shadowing by its ring system.

Over 100 high-resolution images taken by the Hubble Space Telescope allowed more than 300 cloud features to be monitored and wind velocities measured.

Between 1994 and 2002, the period when Hubble scrutinised Saturn, it was spring and early summer in its southern hemisphere. Since then, not only has the wind speed decreased, but there is also evidence that the nature of the clouds in the equatorial region has altered.
Researchers, writing in the journal Nature, suggest two reasons for the difference.

First, Saturn's axis or rotation is inclined by 27 degrees, resulting in strong seasonal effects. Secondly, Saturn's rings periodically shade the atmosphere, reducing the amount of energy available.

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