the Sun. Derived from crater counting data from New Horizons, the age of Nix's surface is estimated to be at least four billion years old. Rotation Nix is not tidally locked and tumbles chaotically similarly to all smaller moons of Pluto; the moon's axial tilt and rotation period vary greatly over short timescales. Due to the chaotic rotation of Nix, it can occasionally flip its entire rotational axis. The varying gravitational influences of Pluto and Charon as they orbit their barycenter causes the chaotic tumbling of Pluto's small moons, including Nix. The chaotic tumbling of Nix is also strengthened by its elongated shape, which creates torques that act on the object. At the time of the New Horizons flyby, Nix was rotating with a period of 43.9 hours retrograde to Pluto's equator with an axial tilt of 132 degrees — it was rotating backwards in relation to its orbit around Pluto. The rotation rate of Nix had increased by 10 percent since Nix was discovered. Features Orbit Nix orbits the Pluto-Charon barycenter at a distance of , between the orbits of Styx and Kerberos. All of Pluto's moons including Nix have very circular orbits that are coplanar to Charon's orbit; the moons of Pluto have very low orbital inclinations to Pluto's equator. The nearly circular and coplanar orbits of Pluto's moons suggest that they may have gone through tidal evolutions since their formation. At the time of the formation of Pluto's smaller moons, Nix may have had a more eccentric orbit around the Pluto-Charon barycenter. The present circular orbit of Nix may have been caused by Charon's tidal damping of the eccentricity of Nix's orbit, through tidal interactions. The mutual tidal interactions of Charon on Nix's orbit would cause Nix to transfer its orbital eccentricity to Charon, thus causing the orbit of Nix to gradually become more circular over time. Nix has an orbital period of 24.8546 days and its orbit is resonant with other moons of Pluto. Nix is in a 3:2 orbital resonance with Hydra, and a 9:11 resonance with Styx (the ratios represent numbers of orbits completed per unit time; the period ratios are the inverses). As a result of this "Laplace-like" 3-body resonance, it has conjunctions with Styx and Hydra in a 2:3 ratio. Nix's orbital period is close to a 1:4 orbital resonance with Charon, with a timing discrepancy of 2.8%; there is no active