'Ring Rain' Bombards Saturn's Atmosphere, Changing the Planet's Climate

In Saturn's atmosphere, charged water particles fall across large areas of the planet. This bombardment of "rain" can actually influence the composition and temperature of parts of Saturn's upper atmosphere. New research reveals exactly where this rain is falling and how much of this significant interaction is occurring between the planet's atmosphere and ring system.

The new findings, published in the journal Nature, were made in part by the W.M Keck Observatory in Mauna Kea, Hawaii. The near-infrared wavelengths that the observatory detected revealed three dark bands on Saturn, which were first observed in the early 1980s in images from NASA's Voyager spacecraft. The better imaging from the observatory in Hawaii allowed researchers to more closely observe the rain's effect in these rings.

The actual 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. Researchers tracked the pattern of emissions of a particular hydrogen ion with three protons. Although they expected to see a uniform, planet-wide infrared glow, they instead saw a series of light and dark bands. The areas of reduced emissions corresponded with water-dense portions of Saturn's rings. Areas of high emission correspond to gaps in the rings.

So what was happening exactly? Charged water particles from the planet's rings were being drawn toward the planet along Saturn's magnetic field lines. These neutralized the glowing triatomic hydrogen atoms and left large "shadows" in what would otherwise be a planet-wide infrared glow.

"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 overhead," said Kevin Baines, co-author of the paper, in a press release. "The ring particles affect both what species of particles are in this part of the atmosphere and where it is warm or cool."

The findings reveal why for many decades observations have shown electron densities to be unusually low at certain latitudes on Saturn. In addition, the research may help scientists better understand the origin and evolution of Saturn's ring system and the changes in the planet's atmosphere.