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. The only known exception is Saturn's natural satellite Hyperion, which rotates chaotically because of the gravitational influence of Titan.
In contrast, the outer natural satellites of the gas giants (irregular satellites) are too far away to have become locked. For example, Jupiter's natural satellite Himalia, Saturn's natural satellite Phoebe, and Neptune's natural satellite Nereid have rotation periods in the range of ten hours, while their orbital periods are hundreds of days.
Read more about this topic: Natural Satellite
Famous quotes containing the word tidal:
“And now it is once more the tidal wave
That when it was swept by, leaves summits stained.
Oh, blood will out. It cannot be contained.”
—Robert Frost (1874–1963)