Monster Storm on Saturn Dredges Ice and Water from Atmosphere's Depths

About once every 30 years, or just once every Saturnian year, a monster storm rips across the ringed planet's surface. This massive tempest can grow to superstorm proportions quickly. In fact, in 2010 the storm reached more than 9,300 miles in width and was visible to amateur astronomers on Earth. Now, scientists have used NASA's Cassini orbiter in order to better understand this storm and the composition of the planet's atmosphere.

Usually, the depths of Saturn's atmosphere are obscured by a thick high-altitude haze. Yet as the storm churned the gases on the planet, scientists were able to use near-infrared color signatures to piece together exactly what this atmosphere looks like. They found that the cloud particles at the top of the massive storm are composed of a mix of three substances: water ice, ammonia ice and an uncertain third ingredient that was probably ammonium hydrosulfide. What is most intriguing is the fact that water ice has been found on the planet, something that researchers had never before seen.

"We think this huge thunderstorm is driving these cloud particles upward, sort of like a volcano bringing up material from the depths and making it visible from outside the atmosphere," said Lawrence Sromovsky, one of the researchers, in a news release. "The upper haze is so optically pretty thick that it is only in the stormy regions where the haze is penetrated by powerful updrafts that you can see evidence for the ammonia ice and water ice. Those storm particles have an infrared color signature that is very different from the haze particles in the surrounding atmosphere."

In fact, Saturn's atmosphere is a bit like a multi-layered cake. There's a layer of water clouds at the bottom, ammonia sulfide clouds in the middle and ammonia clouds near the top, just below an upper tropospheric haze of unknown material that obscures almost anything. As the storms tear across Saturn, though, this layered cake of gases is mixed, revealing more about its composition.

The findings reveal a little bit more about Saturn's atmosphere. In addition, the new research validates the models of Saturn's great storms in addition to previous observations that detected water and ammonia in vapor form.

The findings are published in the journal Icarus.