Satellite libration is likely a common phenomenon. There are suggestions that Titan librates (Lorenz et al., Science 319, 2008) and theoretical arguments that Europa may also librate (Van Hoolst et al., Icarus 195, 2008). Depending on Enceladus’ shape and internal structure, it is possible that this moon physically librates as it orbits Saturn (Porco et al., Science 311, 2006) as well. Cassini ISS has tried to place observational limits on Enceladus’ libration and estimates that its amplitude is at most 1.5o (Porco et al., 2006). A physical libration can produce a diurnal oscillation in the longitude of the tidal bulge and it will have an effect on the diurnal stresses generated on the surface of Enceladus as it orbits Saturn. Changing the character of the diurnal stress affects geological processes controlled by tides. For example, Hurford et al. (LPSC 2008) have shown that strike slip motion driven by tidal walking would be affected by the change in diurnal stress caused by a physical libration. In addition, cracks on Enceladus experience tension and compression across them daily (Hurford et al., Nature 447, 2007) and a physical libration can change the timing of this daily cycle, possibly affecting the location and timing of eruptions on Enceladus. In addition, to the extent that tides produce heat along fractures (Nimmo et al., Nature 447, 2007), libration may affect the magnitude and distribution of such tidal shear heating. Observable effects of these geological processes may provide evidence for this libration. Here we present how a physical libration affects these tidal processes and speculate how Cassini data may be used to detect its existence. A possible libration state for Enceladus is important since it could provide an additional source of heat to drive the eruptions observed from its south polar region.
AAS/Division for Planetary Sciences Meeting Abstracts #40
- Pub Date:
- September 2008