Saturn’s Rings Are Raining on Planet

Saturn and its rings taken over a period of three hours by the wide-angle camera on the Cassini spacecraft. (NASA)

The old adage “April showers bring May flowers” may take on new meaning with the release of a new NASA-funded study tracking the rain of charged water particles from Saturn’s famous rings into the planet’s atmosphere.

The study, led by the University of Leicester, England, found there’s more of this rain and its spread over larger areas than previously thought. Researchers also found the rain influences both the composition and  temperature structure of the ringed planet’s upper atmosphere.

“Saturn is the first planet to show significant interaction between its atmosphere and ring system,” said James O’Donoghue, the paper’s lead author and a postgraduate researcher at Leicester. “The main effect of ring rain is that it acts to ‘quench’ the ionosphere of Saturn. In other words, this rain severely reduces the electron densities in regions in which it falls.”

Artist concept illustrating how charged water particles flow into Saturn’s atmosphere from the planet’s rings, causing a reduction in atmospheric brightness. (NASA/University of Leicester)

The  study gives scientists a better understanding of the origination and evolution of Saturn’s rings, as well as of changes that have taken place in the planet’s atmosphere.

“It turns out that a major driver of Saturn’s ionospheric environment and climate across vast reaches of the planet are ring particles located some 36,000 miles [60,000 kilometers] overhead,” said Kevin Baines, of NASA’s Jet Propulsion Laboratory. “The ring particles affect both what species of particles are in this part of the atmosphere and where it is warm or cool.”

After examining images sent back to Earth from NASA’s Voyager mission in the early 1980s, scientists noticed three dark bands on Saturn, which led them to theorize that water could be showering down into those bands from the rings.

The study authors say those dark bands were not seen again until scientists involved with this research project observed the planet in near-infrared wavelengths with the W.M. Keck Observatory in Hawaii in April 2011.

The effect the rings had on the dark bands was difficult for scientists to distinguish because doing so required that they look for a faint emission that originated from the brightly-lit parts of Saturn. To be able to do this, the researchers needed to use a special tool, available at the Keck Observatory that is able to split up a large range of light into wavelengths.

Image of Saturn’s rings taken from the Cassini spacecraft showing different rings have slightly different colors. The ring particles are mostly light water-ice. (NASA)

Based on their research, the scientists presumed the charged water particles pouring from Saturn’s rings are being pulled towards the planet along its magnetic field lines, while also are working to counteract the expected glow produced by special triatomic (3 atom molecules) hydrogen ions.

So, rather than the entire planet shimmering in an infrared glow, the rain particles creat shadows that cover between 30 to 43 percent of  Saturn’s upper atmosphere surface from around 25 to 55 degrees latitude. This finding indicates a much larger area of shadow cover than was suggested by NASA’s Voyager images of the 1980s.

“Where Jupiter is glowing evenly across its equatorial regions, Saturn has dark bands where the water is falling in, darkening the ionosphere,” said Tom Stallard, a paper co-author at Leicester. “We’re now also trying to investigate these features with an instrument on NASA’s Cassini spacecraft. If we’re successful, Cassini may allow us to view in more detail the way that water is removing ionized particles, such as any changes in the altitude or effects that come with the time of day.”