Hyperion

Hyperion is the largest highly irregular (non-spherical) body in the solar system. Proteus is quite a bit larger but is almost spherical. It seems likely that Hyperion is a fragment of a larger body that was broken by a large impact in the distant past.

   Like most of Saturn's moons, Hyperion's low density indicates that it is composed of water ice with only a small amount of rock.

Hyperion is the only known body in the solar system that rotates chaoticly but simulations seem to indicate that other irregular satellites may have done so in the past. Hyperion is unique in that it is very irregularly shaped, has a highly eccentric orbit, and is near another large moon (Titan). These factors combine to restrict the set of conditions under which stable rotation is possible. The 3:4 orbital resonance between Titan and Hyperion may also make chaotic rotation more likely.

   Hyperion's odd rotation probably accounts for the fact that Hyperion's surface is more or less uniform, in contrast to many of Saturn's other moons which have distinctly different leading and trailing hemispheres. 

Iapetus

All of Saturn's moons except for Iapetus and Phoebe are very nearly in the plane of Saturn's equator. Iapetus is inclined almost 15 degrees. 

Phoebe

   Most of Saturn's moons are bright but Phoebe's albedo is very low (.05), as dark as lampblack.

   All of Saturn's moons except for Phoebe and Iapetus orbit very nearly in the plane of Saturn's equator. Phoebe's orbit is inclined almost 175° (its north pole is in the opposite direction to Saturn's).

   Phoebe's eccentric, retrograde orbit and unusual albedo indicates that it may be a captured asteroid or Kuiper Belt object.

   Phoebe is also unusual in that it does not rotate synchronously as do all the other moons of Saturn except Hyperion.

   Material knocked off of Phoebe's surface by microscopic meteor impacts may be responsible for the dark surfaces of Hyperion and the leading hemisphere of Iapetus.