Tidal Dissipation and Forced Libration in Enceladus
Abstract
One of the puzzling phenomena discovered by the Cassini mission is the existence of strong geysers ejecting plumes of water near the South Pole of Enceladus. These plumes evidence the existence of heat sources in the interior of the satellite, much more strong than the 1 GW indicated by classical tidal theories when the Kelvin's formula for the Love number and arbitrarily fixed values for the rigidity are used. If more realistic values of the Love number is used, the dissipation obtained with classical models is of the order of the observed values, estimated at 5-16 GW. The creep tide theory indicates that the observed heat flow is simply due to the low viscosity of the outer layers (ice near the melting point). The comparison with Mimas, with no tectonic activity due to internal heating and viscosity at least one order of magnitude larger (ice at temperatures well below the melting point) are a clue for the existence, in Enceladus, of a non-stationary process in which an increase in temperature decreases the viscosity and consequently increases the heat dissipation, and so on cyclically. Such a process may have been triggered by some transitory event enhancing the eccentricity of Enceladus and may have been progressing slowly, subsisting even after the eccentricity was damped to its current value. On the other hand, Enceladus presents a forced libration that cannot be explained with a tidal theory for homogeneous bodies. Consequently, with the proposed non-stationary process, the presence of an internal ocean may decouple rotationally the crust from the interior, allowing a greater amplitude of libration.
- Publication:
-
EPSC-DPS Joint Meeting 2019
- Pub Date:
- September 2019
- Bibcode:
- 2019EPSC...13..947F