A giant storm swirls all the way around Saturn in this 2010 view from the Cassini spacecraft. Such storms have popped up in Saturn's atmosphere every few decades, and they can last for months. [NASA/JPL/SSI]
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Moon and Saturn
The Moon and the planet Saturn snuggle quite close tonight. Saturn is just to the lower right of the Moon at nightfall, and looks like a bright star.
Seen through a telescope, Saturn itself usually looks pretty bland. Its atmosphere is divided into bands that are tinted in subtle shades of yellow and tan. Storms twirl through those bands, but they’re difficult to see from Earth.
Most of the time, that is. Every few decades, a giant storm bursts into view. Its white core is as big as Earth. And in months, it can stretch half way around the planet.
The storms are like thunderstorms here on Earth. Their clouds are made of water vapor, and they produce lightning and major downpours. The first of these storms was seen in 1876, and the most recent popped up in 2010.
Researchers at Caltech say they know why the storms are so infrequent.
The water in the clouds is much denser than the hydrogen and helium that make up much of Saturn’s atmosphere. So most of the time, the water stays in a layer far below Saturn’s cloudtops.
Eventually, though, the atmosphere above the water gets much colder, which makes it denser. That makes it easier for the warm water vapor to rise high into the atmosphere, creating a massive new storm. But that warms the atmosphere again, so the denser storm quickly rains itself away.
The researchers say it takes several decades for this cycle to play out — leaving a long dry spell between Saturn’s giant storms.
Script by Damond Benningfield, Copyright 2015