section_path: Tidal locking
section_name: Tidal locking
paragraph_text: Tidal locking
  
  Most regular moons (natural satellites following relatively close and prograde orbits with small orbital inclination and eccentricity) in the Solar System are tidally locked to their respective primaries, meaning that the same side of the natural satellite always faces its planet. This phenomenon comes about through a loss of energy due to tidal forces raised by the planet, slowing the rotation of the satellite until it is negligible. Exceptions are known; one such exception is Saturn 's natural satellite Hyperion, which rotates chaotically because of the gravitational influence of Titan. Pluto's four, circumbinary small moons also rotate chaotically due to Charon's influence.
  
  In contrast, the outer natural satellites of the giant planets (irregular satellites) are too far away to have become locked. For example, Jupiter's Himalia, Saturn's Phoebe, and Neptune's Nereid have rotation periods in the range of ten hours, whereas their orbital periods are hundreds of days.