Discovered: Saturn's rings are raining water

Cosmic rain! Astronomers have discovered that the rings of Saturn produce their own rain that falls onto the planet, having a major impact on its atmosphere.
A new study tracked the "rain" of charged water particles into the atmosphere of Saturn and found there is more of it and it falls across larger areas of the planet than previously thought.
The study, whose observations were funded by NASA and whose analysis was led by the University of Leicester, England, reveals that the rain influences the composition and temperature structure of parts of Saturn's upper atmosphere.
"Saturn is the first planet to show significant interaction between its atmosphere and ring system," said James O'Donoghue, lead author of the study.

"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," he said in a NASA statement.
O'Donoghue noted the ring's effect on electron densities is important because it explains why, for many decades, observations have shown those densities to be unusually low at certain latitudes on Saturn.

The study, published in the journal Nature, also helps scientists better understand the origin and evolution of Saturn's ring system and changes 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 60,000 kilometres overhead," said Kevin Baines, a co-author of the study.

"The ring particles affect both what species of particles are in this part of the atmosphere and where it is warm or cool," Baines said.
In the early 1980s, images from NASA's Voyager spacecraft showed two to three dark bands on Saturn, and scientists theorised that water could have been showering down into those bands from the rings.
Those bands were not seen again until this team observed the planet in near-infrared wavelengths with the W M Keck Observatory on Mauna Kea, in Hawaii.
The ring rain's effect occurs in Saturn's ionosphere, where charged particles are produced when the otherwise neutral atmosphere is exposed to a flow of energetic particles or solar radiation.

Both Earth and Jupiter have an equatorial region that glows very uniformly. Scientists expected this pattern at Saturn, too, but they instead saw dramatic differences at different latitudes.
"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, co-author of the study.