Shadows of Saturn’s Rings Mess With Its Upper Atmosphere

The Cassini probe’s final swoops through the rings found that they impact the planet’s ionosphere

NASA/JPL-Caltech/Space Science Institute

During the last six months of its 13-year-mission exploring Saturn and its moons, the Cassini spacecraft took 22 “Grand Finale” swoops between the planet and its famous rings, collecting as much data a possible before burning up in Saturn’s atmosphere last September. Since then, researchers have been analyzing the data, discovering that the rings actually impact the planet’s atmosphere, reports Ryan F. Mandelbaum at Gizmodo.

Like Earth, Saturn’s upper atmosphere contains an ionosphere—a layer of particles that have had their electrons ripped off by cosmic rays and radiation from the Sun, creating a mass of positively charged particles. According to a press release, during its final dives, Cassini swooped through the upper reaches of Saturn’s ionosphere using its Radio and Plasma Wave Science instrument to measure the density of ions in the layer. They published their analysis last week in the journal Science.

The result? Saturn’s ionsphere is complex. The shadows cast by Saturn’s A and B rings appear to block solar radiation from reaching the upper atmosphere in areas of the planet's southern hemisphere. This prevents ionization of molecules and overall lower ion density. 

As Andrew Wagner at Science reports, there was still some activity within the shadow zone. Researchers theorize that this might be caused by the planet’s innermost D ring. It’s possible that charged water particles are migrating from the ring to the ionosphere in a phenomenon called “ring rain.” As Mandelbaum reports, the new data could help researchers figure out how particles move around the giant planet’s atmosphere, and could help them create models for far off exoplanets.

Deborah Netburn at the L.A. Times reports that the planet’s ionosphere is more variable and much more complex than researchers initially thought. There’s still much they don’t know but in the next few months more papers based on other instruments that were active during Cassini’s final dives will help flesh out the picture. “Consider this a prelude of things to come from Cassini,” Hunter Waite, director of planetary mass spectrometry at the South West Research Institute, not involved in the study tells Netburn. “Saturn’s ionosphere is much more complicated than anyone could imagine.”

William Kurth from the University of Iowa tells Mandelbaum that the data from this latest paper are preliminary. That’s because they are only based on Cassini’s first 11 dives and do not include the final dive when it went deeper into the atmosphere. In fact, Cassini had eight instruments collecting data during its final death plunge, which means we’ll be getting new information on Saturn for a long time to come.