Discovery Files

Hundred-year storms? That's how long they last on Saturn

Megastorms leave marks on Saturn's atmosphere for centuries

The largest storm in the solar system, a 10,000-mile-wide anticyclone called the Great Red Spot, has decorated Jupiter's surface for hundreds of years.

A new study now shows that Saturn — though much blander and less colorful than Jupiter — also has long-lasting megastorms with impacts deep in the atmosphere that persist for centuries.

The study was conducted by astronomers at the University of California, Berkeley and the University of Michigan who looked at radio emissions from the planet, which come from below the surface. The scientists found long-term disruptions in the distribution of ammonia gas. The study is published in Science Advances.

Megastorms occur approximately every 20 to 30 years on Saturn and are similar to hurricanes on Earth although significantly larger. Unlike Earth's hurricanes, no one knows what causes megastorms in Saturn's atmosphere, which is composed mainly of hydrogen and helium, with traces of methane, water and ammonia.

Imke de Pater, a UC Berkeley astronomer, has been studying gas giants for more than four decades to better understand their composition and what makes them unique, employing the Karl G. Jansky Very Large Array to probe the radio emissions from deep inside the planet. The VLA is part of the National Radio Astronomy Observatory, a facility of the U.S. National Science Foundation, operated under cooperative agreement by Associated Universities Inc.

"Understanding the mechanisms of the largest storms in the solar system puts the theory of hurricanes into a broader cosmic context, challenging our current knowledge and pushing the boundaries of terrestrial meteorology," said lead author Cheng Li. "At radio wavelengths, we probe below the visible cloud layers on giant planets. Radio observations help characterize dynamical, physical and chemical processes."

The researchers found something surprising in the radio emissions from the planet: anomalies in the concentration of ammonia gas in the atmosphere, which they connected to the past occurrences of megastorms in the planet's northern hemisphere.

According to the team, the concentration of ammonia is lower at midaltitudes, just below the uppermost ammonia-ice cloud layer, but has become enriched at lower altitudes, 100 to 200 kilometers deeper in the atmosphere. They believe that the ammonia is being transported from the upper to the lower atmosphere by precipitation and reevaporation. That effect can last for hundreds of years.