RSAA Colloquia / Seminars / Feast-of-Facts: Thursday, 01 February 2018, 11:00-12:00; Duffield Lecture Theatre

Alice Quillen

"Soft astronomy: Astro-visco-elastic dynamics"

Close tidal encounters among large planetesimals and moons were more common than impacts. Using a mass spring model within an N-body simulation, we simulate the small deformation of a surface that is caused by a close tidal encounter. We find tidal encounters can induce sufficient stress on the surface to cause large scale brittle failure of an icy crust. Strong tidal encounters may be responsible for the formation of long graben complexes and chasmata in ancient terrain of icy moons such as Dione, Tethys, Ariel and Charon. Mass spring models, originally developed for graphics and gaming applications, can measure remarkably small deformations and so can show tidal spin down of viscoelastic objects, directly tying simulated rheology to orbital drift and internal heat generation. The new Horizons mission discovered that Pluto and Charon’s minor satellites Styx, Nix, Kerberos, and Hydra, are rapidly spinning, but surprisingly they have spin axis tilted into the orbital planet (they have high obliquities). Long simulations of the minor satellites in a drifting Pluto-Charon binary system exhibit rich resonant spin dynamics, including spin-orbit resonance capture, tumbling resonance and spin-binary resonances. We have identified spin-precession mean-motion resonances with Charon that can lift obliquities in the Pluto/Charon system.