What is it?
The rings of Saturn are composed ~99% water ice (yes, H2O!) and pieces of its fragmented structure range in size from collections of molecules to bus-sized chunks. Smaller parts of this material are churned up by meteoric impacts and ionized by sunlight, leading to the formation of a charged ring atmosphere (a ‘ring ionosphere’). Charged material is able to feel the magnetic field of Saturn, so when given a kick in the right direction some of the material then follows the magnetic field lines into the planetary atmosphere, falling as ‘ring rain’ – ta da!
In 2013, using data from 2011, we found for the first time that there is an imprint of ring rain is in the upper atmosphere of Saturn. Not only that, but we found that the water influx from the rings actually dominates the chemical environment where it falls – at approximately 43 degrees north and 37 south latitude. Below are a couple of figures to explain what’s going on.
Below: Arty illustration of ring rain, slightly before we really understood it!
We now think the water is just coming in at two locations denoted in yellow below, but possibly other narrow areas too. We measure H3+, a molecular ion in the atmosphere, finding that the emission from it was higher in regions of expected water influx. The emission is higher because the incoming water acts to soak up H3+ destroying electrons – so in other words, water takes away a loss mechanism of H3+, letting more of it “survive” to emit.
You can find the corresponding paper in the scientific journal Nature, where we published this finding in 2013. You can also see a companion article written by Jack Connerney, who first discovered evidence of ‘ring rain’ in the 1980s here.