"If you lived on one of Pluto's moons Nix or Hydra, you'd have a hard time setting your alarm clock. That's because you could not know for sure when, or even in which direction, the sun would rise. A comprehensive analysis of all available Hubble Space Telescope data shows that two of Pluto's moons, Nix and Hydra, are wobbling unpredictably. Scientists believe the other two moons, Kerberos, and Styx, are likely in a similar situation, pending further study."
- Resonant interactions and chaotic rotation of Pluto's small moons, Nature (it costs $32 to read this article if you do not subscribe to Nature)
- Update: The text is online here - for free.