2008/02/20 by Yoram Lithwick, Lithwick, Yoram, Yanqin Wu +1
Engineering · Physics and Astronomy · #Astro and Planetary Science #Astrophysics (astro-ph) #FOS: Physical sciences #Planetary Science and Exploration #Spacecraft and Cryogenic Technologies #astro-ph
paper · pdf · doi:10.48550/arxiv.0802.2939
12 pages, submitted to ApJ
arxiv created 2008/02/20 · openalex publication_date 2008/02/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Pluto's recently discovered minor moons, Nix and Hydra, have almost circular orbits, and are nearly coplanar with Charon, Pluto's major moon. This is surprising because tidal interactions with Pluto are too weak to damp their eccentricities. We consider an alternative possibility: that Nix and Hydra circularize their orbits by exciting Charon's eccentricity via secular interactions, and Charon in turn damps its own eccentricity by tidal interaction with Pluto. The timescale for this process can be less than the age of the Solar System, for plausible tidal parameters and moon masses. However, as we show numerically and analytically, the effects of the 2:1 and 3:1 resonant forcing terms between Nix and Charon complicate this picture. In the presence of Charon's tidal damping, the 2:1 term forces Nix to migrate outward and the 3:1 term changes the eccentricity damping rate, sometimes leading to eccentricity growth. We conclude that this mechanism probably does not explain Nix and Hydra's current orbits. Instead, we suggest that they were formed in-situ with low eccentricities. We also show that an upper limit on Nix's migration speed sets a lower limit on Pluto-Charon's tidal circularization timescale of >105 yrs. Moreover, Hydra's observed proper eccentricity may be explained by the 3:2 forcing by Nix.