Open AccessA solar system survey of forced librations in longitude
Author(s) -
Comstock Robert L.,
Bills Bruce G.
Publication year - 2003
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2003je002100
Subject(s) - libration (molecule) , physics , eccentricity (behavior) , amplitude , asteroid , solar system , orbit (dynamics) , longitude , orbital eccentricity , orbital inclination , orbital elements , mean motion , planet , spin (aerodynamics) , orbital motion , angular momentum , astrophysics , classical mechanics , astronomy , latitude , geometry , optics , political science , law , thermodynamics , aerospace engineering , point (geometry) , mathematics , engineering , arithmetic , binary number
Forced librations are periodic rotational rate variations due to gravitational interactions with an orbital partner. We have developed an analytic theory capable of calculating expected amplitudes of forced librations for nonresonant rotators as well as for bodies existing in a spin‐orbit resonance. The theory has been applied to 34 solar system bodies, including terrestrial planets, planetary satellites, and the asteroid Eros. Parameters governing libration amplitude are the body's orbital eccentricity, moment difference, and the ratio of its spin rate to its orbital rate. In each case the largest libration amplitude is associated with the forcing frequency 2 ( p − 1) n , where n is the orbital mean motion and p is the spin/orbit rate ratio. This dominant frequency is simply semidiurnal as seen from the position of the torquing body. The maximum libration angular amplitude is 1.3 × 10 −2 radians for Thebe, and the maximum mean equatorial displacement is 1.4 km for Mimas.