Taller de Ciencias Planetarias - 2018

Forced Rotational Oscillations Amplify the Tidal Dissipation of Enceladus

Sylvio Ferraz-Mello, Hugo A Folonier and Eduardo Andrade-Ines

Universidade  de São Paulo

One of the puzzling phenomena discovered by the Cassini mission is the existence of strong geysers ejecting plumes of water and ice. These plumes evidence the existence of heat sources in the interior of Enceladus much more efficient than indicated by classical tidal theories. The heat flowing through Enceladus surface is estimated at 5-16 GW and the tidal heat generation was estimated at ~1 GW only. We propose (Cel. Mech. Dyn. Astron. in press; ArXiv astro-ph 1707-09229) a modification in the classical tidal theories in which the average value of the dissipation considers the fact that the rotational motion of the satellite is not exactly synchronous but, as indicated by our recent tidal theory, the rotation is trapped in an attractor where its actual velocity has a forced oscillation around the synchronous value. As a result, the dissipation in Enceladus is one order of magnitude larger than obtained when a stationary synchronous motion is assumed. The heat flow estimated from Cassini observations is obtained assuming for the relaxation of the satellite $2-6 \times 10^{-8}  s^{-1}$, which corresponds to values of the viscosity $0.5-1.5 \times 10^{-15}$ Pa.s in the same range as adopted in the modeling of the phenomenon by several authors (e.g. Behounková et al. 2012).

Sponsors: CNPq and FAPESP (Brasil)