IGPP Seminar Series

Resonant amplification of forced librations in longitude: application to Enceladus?

by Bruce Bills
(NASA Goddard/UCSD Scripps)

Abstract

Forced librations in longitude are periodic variations in rotation rate due to gravitational torques. In the archetypal case of the Moon, the forcing period (27.55 days) is much shorter than the resonant period (2.9 years), and the response is small. For hypothetical bodies in which the forcing period approaches the resonant period, the amplitude can be appreciable. It has been proposed that Enceladus may approximate a sub-harmonic resonance, in which the forcing period is close to 1/3 of the resonant period. However, if there is an ice shell which is mechanically decoupled from the deeper interior, it may approximate the fundamental resonance, and yield large amplitude librations. I examine several aspects of this problem, including stability and energetics.
Tuesday, 29 May 2007
3853 Slichter Hall
Refreshments at 3:45 PM
Lecture at 4:00 PM