The Relative Motion and Shapes of Pluto and Charon

The comparative effect of two factors on the translatory motion of the centers of mass of the Pluto–Charon system is investigated. The first important factor is the non-sphericity of the shape and gravitational field of the bodies in the system. The second factor is the gravitation of the Sun. As a measure of the influence of both factors we use the ratio of the corresponding perturbing acceleration to the main one. The main acceleration is caused by the mutual Newtonian attraction of Pluto and Charon. It has been established that for the first factor this measure is on the order of 10–6, while for the second factor it is two orders of magnitude smaller. This explains why the Lidov–Kozai effect (despite a large mutual slope of 96° between the planes of the satellite’s orbit around the planet, and the barycenter of the system around the Sun) does not appear. The situation is similar to the case with the satellites of Uranus. As a result, the Pluto–Charon system remains stable at least on a timescale of millions of years. The tidal effect of the Sun on the surface shape of the bodies under study is also estimated. The ratio of the tidal potential of the Sun at a point on the surface of the body to the gravitational potential of the body itself at this point is taken as a measure of impact. It turned out to be on the order of 3 × 10–12, which is more than six orders less than the influence of rotation and mutual attraction of Pluto and Charon. In fact, the Sun does not affect the figures of the bodies of the system.

[1]  Complete tidal evolution of Pluto–Charon , 2014, 1402.0625.

[2]  H. Weaver,et al.  The Pluto System After New Horizons , 2017, Annual Review of Astronomy and Astrophysics.

[3]  David E. Smith,et al.  The Ceres gravity field, spin pole, rotation period and orbit from the Dawn radiometric tracking and optical data , 2018 .

[4]  E. D. Kuznetsov,et al.  The Expansion of the Hamiltonian of the Planetary Problem into the Poisson Series in All Keplerian Elements (Theory) , 2001 .

[5]  C. Russell,et al.  A partially differentiated interior for (1) Ceres deduced from its gravity field and shape , 2016, Nature.

[6]  Berkeley,et al.  The gravity field and interior structure of Dione , 2019, Icarus.

[7]  M. L. Lidov.  The evolution of orbits of artificial satellites of planets under the action of gravitational perturbations of external bodies , 1962 .

[8]  S. W. Asmar,et al.  The Gravity Field and Interior Structure of Enceladus , 2014, Science.

[9]  S. Asmar,et al.  Gravity field and interior of Rhea from Cassini data analysis , 2007 .

[10]  S. Sadov.  Analytic properties of Hansen coefficients , 2008 .

[11]  P. Thomas.  Sizes, shapes, and derived properties of the saturnian satellites after the Cassini nominal mission , 2010 .

[12]  Yoshihide Kozai,et al.  Secular perturbations of asteroids with high inclination and eccentricity , 1962 .

[13]  K. V. Kholshevnikov,et al.  On the asphericity of the figures of Pluto and Charon , 2019 .

[14]  D. E. Jennings,et al.  The small satellites of Pluto as observed by New Horizons , 2016, Science.

[15]  M. W. Buie,et al.  Orbits and Photometry of Pluto’s Satellites: Charon, S/2005 P1, and S/2005 P2 , 2005, astro-ph/0512491.

[16]  Francis Nimmo,et al.  Mean radius and shape of Pluto and Charon from New Horizons images , 2017 .

[17]  M. Showalter,et al.  The orbits and masses of satellites of Pluto , 2015 .