How Charged Water Particles Affect Saturn's Atmosphere
April 10, 2013

How Charged Water Particles Affect Saturn’s Atmosphere

Lee Rannals for — Your Universe Online

A new study published in the journal Nature found that the "rain" of charged water particles in Saturn's atmosphere influences the composition and temperature of the planet's upper atmosphere and rings.

The study, led by the University of Leicester in England, reveals that there is a significant interaction between its atmosphere and ring system.

"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," said James O'Donoghue, the paper's lead author and a postgraduate researcher at Leicester.

He said the ring's effect on electron densities is important because it explains why observations have shown those densities to be unusually low at certain latitudes on Saturn.

The researchers' study helps scientists have a better understanding of the origin and evolution of Saturn's ring system and the changes in the ringed 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, a co-author on the paper, based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "The ring particles affect both what species of particles are in this part of the atmosphere and where it is warm or cool."

Images taken by NASA's Voyager spacecraft in the 1980s showed two to three dark bands on Saturn, which were not seen again until this team observed the planet in near-infrared wavelengths in April 2011. They were able to observe a series of light and dark bands, with areas of reduced emission corresponding to water-dense portions of Saturn's rings and areas of high emission corresponding to gaps in the rings.

The team said that charged water particles from the planet's rings were being drawn towards the planet along Saturn's magnetic field lines and were neutralizing the glowing triatomic hydrogen ions. This process leaves "shadows" that cover 30 to 43 percent of the planet's upper atmosphere surface from around 25 to 55 degrees latitude.

"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."

In 2012, scientists studying images from NASA's Cassini spacecraft found evidence of massive snowballs dragging trails from one of Saturn's rings. Scientists said disturbances in the planet's F ring have helped to create giant, half-mile-wide snowballs. The discovery of these snowballs helps scientists understand how planetary bodies interact with other objects in space.