Mystery behind Saturn's Great White Spots 'tantrums' resolved

Researchers have revealed that giant storms on Saturn known as "Great White Spots" may be caused by moisture in the planet's atmosphere.

Every 20 to 30 years, Saturn's atmosphere roils with giant, planet-encircling thunderstorms that produce intense lightning and enormous cloud disturbances.

Six such storms have been observed on Saturn over the past 140 years, alternating between the equator and midlatitudes, with the most recent emerging in December 2010 and encircling the planet within six months. The storms usually occur when Saturn's northern hemisphere is most tilted toward the sun. Just what triggers them and why they occur so infrequently, however, has been unclear.

Now, a new study by two Caltech planetary scientists suggested that a possible cause for these storms. Using numerical modeling, Professor of Planetary Science Andrew Ingersoll and his graduate student Cheng Li simulated the formation of the storms and found that they may be caused by the weight of the water molecules in the planet's atmosphere.

Because these water molecules are heavy compared to the hydrogen and helium that comprise most of the gas-giant planet's atmosphere, they make the upper atmosphere lighter when they rain out, and that suppresses convection.

Over time, this leads to a cooling of the upper atmosphere. But that cooling eventually overrides the suppressed convection, and warm moist air rapidly rises and triggers a thunderstorm.

The study is published in the journal Nature Geoscience.