Secular rotational dynamics of quasi-binary systems: Pluto-Charon

Abstract

It is believed that Pluto-Charon is in a double (1:1) synchrounism. It is a very particular system: Pluto eccentricity (0.2) is similar to Mercury’s one, however they have different obliquities: Pluto s obliquity varies in the range 103 to 128 degrees, while Mercury s obliquity is constant, almost zero. Differently from some authors, we will take Andoyer variables, in 3D space. Besides, we consider Pluto and Charon as 2 separated bodies, not a single rigid piece. Threfore we can study the possibility of double 1:1 synchrounism. With the use of Andoyer variables, we can show that spin-orbit resonance, in the absence of tides, makes sense only if C22 is not zero, for any kind of spin-orbit resonance. As we consider Pluto and Charon two independent masses, we can study the equator precession of each body and the individual perturbation caused by them. Our methology will serve to the 3:2 resonance case, however the amount of the cosines for this case (some thousands of terms) may require additional effort and time. Even so, we intend to build the corresponding V disturbing potential for this case and compare 3:2 spin orbit resonance to 1:1 case. Finally, the investigation of Pluto-Charon system, as proposed here, becomes very interesting, since New Horizons mission should collect modern new data, which can be used to teste and validate our results. (AU)