Self-tuned tidal resonance and the heating of oceans on icy satellites in the Solar System (and Universe)

English Abstract:

Observations by the Galileo and Cassini spacecrafts have provided a strong indication that our massive water ocean is only one of at least several others in the Solar System. It seems clear that these oceans would have long ago frozen if not for an internal heat source. It also seems clear that in at least some of these cases (e.g. Enceladus), the heat sources previously presumed are insufficient. Recently, it has been shown by the author that if these oceans occupy one of several plausible resonant configurations, then the tidal response and associated dissipative heat can easily maintain liquid oceans on most of the large satellites in close orbits. It has also been shown that these resonant configurations are not just possible but may be inevitable because of a self-tuning effect; as an ocean attempts to freeze, it's eigenmodes are altered and it is pushed into the resonant configurations, with the increase in heat acting to stall further freezing.

More specifically, study of the parameter space of ocean tidal scenarios (where the parameters controlling the tidal response act as coordinates) show that energetic, resonantly forced tidal scenarios are stable configurations, at least until the available tidal energy in the orbit has been expended. Conversely, a satellite with thick ice and no water ocean is possible only if one or more of the following apply: 1) There was never once a liquid ocean; 2) Available tidal forces were once insignificant, allowing the ocean to freeze; 3) The idealizations used in this study were once invalid for the ocean considered. Because of this expected feedback and self-tuning effect, a forward speculation is therefore that liquid oceans may be very common in the Universe.