After observing near-infrared spectral measurements taken by NASA's Cassini spacecraft, researchers have detected the presence of ammonia and water ice in the depths of Saturn's atmosphere.
Once in every 30 years, a massive storm rips across the northern hemisphere of Saturn. This period is said to be roughly one Saturnian year. The sixth, most recent and only Saturnian storm observed by mankind began brewing in 2010. The storm soon developed into a super-storm, covering a distance of 15,000 kilometers. The storm was visible to even amateur astronomers and looked like a great white spot dancing across the surface of the ringed planet from Earth.
Researchers from the University of Wisconsin-Madison studied near-infrared spectral measurements taken by NASA's Cassini spacecraft of the storm. They were able to shed an in-depth light on the composition of Saturn's atmosphere, which is usually obstructed by a thick high-altitude haze.
Researchers discovered the presence of water ice, ammonia ice, and an uncertain third constituent that is possibly ammonium hydrosulfide in cloud particles atop the storm. This is the first time water in the form of ice has been discovered on the planet.
"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," Lawrence Sromovsky, a senior scientist at UW-Madison and an expert on planetary atmospheres, said in a press 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 the water ice. Those storm particles have an infrared color signature that is very different from the haze particles in the surrounding atmosphere."
The recent discovery has led scientists to speculate that Saturn may have a layered atmosphere. Ammonia hydrosulfide clouds may be sandwiched between water clouds at the bottom and ammonia clouds on top. All three layers are covered by a high haze of unknown composition.
The presence of the Cassini probe orbiting the ringed planet has given scientists the opportunity to observe and study Saturn's atmosphere beneath this thick haze. Researchers found that the Saturnian storm works in the same manner as similar events that take place on Earth, where air and water vapor are pushed high into the atmosphere, resulting in the towering, billowing clouds of a thunderstorm. However, storms on Saturn are bigger and more violent, traveling at a speed of more than 300 miles per hour.
"It starts at the water cloud level and develops a huge convective tower. It is similar to a big thunderstorm, only 10 to 20 times taller and covering an even greater area," Sromovsky explained.
The new findings also confirm previous ones of water and ammonia in vapor form on Saturn. The finding of water ice on the planet supports the idea that Saturn's super-storms are powered by condensation of water and that these storms originate deep in the atmosphere, about 200 kilometers below the visible cloud deck.
