Ring rain influences Saturn’s atmosphere
8 May 2013 by qmjwtjwqdb.d qmjwtjwqdb.d
Saturn’s atmosphere is home to more charged water particle “rain” than previously thought suggests a study led by the University of Leicester.
Their findings reveal that this rain influences the composition and temperature structure of parts of the planet’s upper atmosphere. The research is published in Nature.
“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.”
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 for many decades.
“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 from NASA’s Jet Propulsion Laboratory and a co-author on the paper. “The ring particles affect both what species of particles are in this part of the atmosphere and where it is warm or cool.”
The team observed the planet in near-infrared wavelengths with the W.M Kech Observatory on Mauna Kea, in Hawaii.
The ring rain’s effect happens 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.
The researchers tracked the pattern of emissions of a hydrogen ion with three protons –triatomic hydrogen. They were expecting to observe a uniform planet-wide infrared glow, but instead witnessed a series of light and dark bands – with areas of reduced emission spectrum corresponding to water-dense portions of Saturn’s rings.
The results revealed that charged water particles from the rings were being drawn towards the planet along Saturn’s magnetic field lines and were able to neutralise the glowing triatomic hydrogen ions, leaving large ‘shadows’ in the otherwise planet-wide infrared glow.
“Where Jupiter is glowing evenly across its equatorial regions, Saturn has dark bands where the water is falling in, darkening the ionosphere. 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 ionised particles, such as any changes in altitude of effects that come with the time of day,” said Tom Stallard, a paper co-author, also from Leicester.
