Saturn Research

My Saturn research is split into two areas: aurorae and “ring rain”. This page is currently under construction [23 July 2016]

Saturn’s ring rain

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 originally thought ring rain came in at multiple locations as depicted in this artists impression, but we think it's mostly falling in at 43N and 38S, but perhaps elsewhere too.

We originally thought ring rain came in at multiple locations as depicted in this artists impression, but we now think it’s mostly falling in at 43N and 38S, with other locations (via unknown mechanisms) too.

We now think the water is just coming in at two locations denoted in yellow below, but possibly other narrow areas too. Essentially 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 (simply put) 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 live, and so more a higher intensity is observed.

The horizontal axes show a scale of planetocentric latitude at the bottom and the planetocentric equatorial distances which those latitudes magnetically map to at the top. The y axis shows the intensity of H3+ emission of the two spectral lines that are shown, Q(1, 0−) at 3.953 µm (black line) and R(2, 2−) at 3.622 µm (dashed black line) with a central gap where the observed emission is swamped by solar photon reflection from the planetary rings. The 1-sigma errors in intensity measurements are denoted by the grey shading envelopes for each line. Latitude bands mapping along planetary magnetic field lines to the main ring subdivisions in the equatorial plane are shown blue (water influx), and the ring gaps are shown in red. The yellow shading is the instability region between the stability limits.

The horizontal axes show a scale of planetocentric latitude at the bottom and the planetocentric equatorial distances which those latitudes magnetically map to at the top. The y axis shows the intensity of H3+ emission of the two spectral lines that are shown, Q(1, 0−) at 3.953 µm (black line) and R(2, 2−) at 3.622 µm (dashed black line) with a central gap where the observed emission is swamped by solar photon reflection from the planetary rings. The 1-sigma errors in intensity measurements are denoted by the grey shading envelopes for each line. Latitude bands mapping along planetary magnetic field lines to the main ring subdivisions in the equatorial plane are shown blue, and the ring gaps are shown in red. The yellow shading denotes the ‘instability regions’ where we think the water influx is mostly coming in from.

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.

Press/public interest was high, see a sample of online coverage by clicking play below.

Saturn’s aurorae