In anticipation of the upcoming New Horizons fly-by of the Pluto system, a really exciting result from Mark Showalter of SETI and Doug Hamilton of UMD — complex gravitational interactions among the moons of Pluto, Charon, Styx, Nix, Kerberos, and Hydra, have driven Nix mad and make it rotate chaotically. A simulation of its rotational evolution is shown in the youtube video above.
Showalter and Hamilton analyzed Hubble images of the Pluto system to understand how the moons’ orbits evolve as the result of the gravitational tugs between the moons. The three moons Styx, Nix, and Hydra are very near to and probably in a three-body resonance reminiscent of the Galilean satellites. Computer models of that interaction allowed them to constrain the masses of the moons, somewhere in the range of Mars’ moon Deimos‘ mass.
We would expect that the complex gravitational environment as applied to such elongated moons would likely lead to complex rotation, and indeed, Showalter and Hamilton find that the phase curve for Nix, observed from 2010 to 2012, varies erratically, consistent with a chaotic rotation. Their analysis also shows that Hydra rotates chaotically; probably some of the other moons (except for Charon) as well.
One bit of good news for the New Horizons flyby emerges from all this: the systems’ chaotic dynamics probably keep it clear of rings or additional small moons that would pose hazards for New Horizons. It seems nature has decided the system is complicated enough already.
Attendees at today’s journal club included Jennifer Briggs, Emily Jensen, and Tyler Wade.