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New Horizons mission observations show that the small satellites Styx, Nix,Kerberos and Hydra, of the Pluto-Charon system, have not tidally spun-down tonear synchronous spin states and have high obliquities with respect to theirorbit about the Pluto-Charon binary (Weaver et al. 2016). We use a dampedmass-spring model within an N-body simulation to study spin and obliquityevolution for single spinning non-round bodies in circumbinary orbit.Simulations with tidal dissipation alone do not show strong obliquityvariations from tidally induced spin-orbit resonance crossing and this weattribute to the high satellite spin rates and low orbital eccentricities.However, a tidally evolving Styx exhibits intermittent obliquity variations andepisodes of tumbling. During a previous epoch where Charon migrated away fromPluto, the minor satellites could have been trapped in orbital mean motioninclination resonances. An outward migrating Charon induces large variations inNix and Styx's obliquities. The cause is a commensurability between the meanmotion resonance frequency and the spin precession rate of the spinning body.As the minor satellites are near mean motion resonances, this mechanism couldhave lifted the obliquities of all four minor satellites. The high obliquitiesneed not be primordial if the minor satellites were at one time captured intomean motion resonances.

Obliquity evolution of the minor satellites of Pluto and Charon