The rotation speed – spin rate – of Saturn was previously found through observations of its magnetic field. Now, scientists have determined the spin rate through ripples in its rings!
NASA’s twin voyager probes, launched over 40 years ago, observed the swirling magnetic field of Saturn, from which it was able to deduce a rotation period for the magnetic field and conclude a spin rate of 10 hours and 40 minutes. During this mission, in the 1980’s, the ring system was observed in great detail revealing the gravitational effects of Saturn’s moons on the rock and ice particles in the rings. When the particles and moons orbit at simple ratios of each other, the particles are periodically kicked by the moons. These kicks, known as orbital resonance, can launch waves that propagate away from the planet – with some anomalous “backwards” waves.
Detailed observations of these waves have been made, since 2000, with NASA’s Cassini spacecraft and the Cassini Visible and Infrared Mapping Spectrometer (VIMS) and now a team of scientists led by Christopher Mankovich have compared this data with the ripples generated from model simulations of Saturn’s internal structure. The results have revealed a more precise spin rate for the planet – 10 hours and 35 minutes – and as well have revealed a greater understanding of Saturn’s internal structure.
“It turns out that Saturn’s rings are an extraordinarily sensitive way of detecting disturbances inside the planet,” says David Stevenson of the California Institute of Technology in Pasadena, California.
The correlation found between the internal dynamics and the exterior rings can be extended for all gas giants and planetary bodies in general. This has huge implications for unified physics, as with such a fundamental understanding confirmed with observations, the model can be extended to planets, stars, galaxies and all rotating systems across all scales.
Paper: https://arxiv.org/abs/1805.10286
