Washington: Once every 30 years or so, or roughly one year in Saturn, a massive storm is formed in the planet which pulls water and ammonia ices from the planet`s depths.
In 2010, the most recent and only the sixth giant storm on Saturn observed by humans began stirring. It quickly grew to superstorm proportions, reaching 15,000 kilometers (more than 9,300 miles) in width and visible to amateur astronomers on Earth as a great white spot dancing across the surface of the planet.
Now, thanks to near-infrared spectral measurements taken by NASA`s Cassini orbiter and analysis of near-infrared color signatures by researchers at the University of Wisconsin-Madison, Saturn`s superstorm is helping scientists flesh out a picture of the composition of the planet`s atmosphere at depths typically obscured by a thick high-altitude haze.
The key finding: cloud particles at the top of the great storm are composed of a mix of three substances: water ice, ammonia ice, and an uncertain third constituent that is possibly ammonium hydrosulfide.
A team led by UW-Madison Space Science and Engineering Center planetary scientists Lawrence Sromovsky, and including Kevin Baines and Patrick Fry, reports the discovery of the icy forms of water and ammonia. Water in the form of ice has never before been observed on Saturn.
Scientists believe Saturn`s atmosphere is a layered sandwich of sorts, with a deck of water clouds at the bottom, ammonia hydrosulfide clouds in the middle, and ammonia clouds near the top, just below an upper tropospheric haze of unknown composition that obscures almost everything.
On Saturn, not only are the storms much bigger, they are far more violent, with models predicting vertical winds of more than 300 miles per hour for these rare giant storms.
The effect, Sromovsky says, is to loft the aerosols found deep in the atmosphere to the visible cloud tops, providing a rare glimpse of normally hidden materials.
The study has been published in the journal Icarus.