Hyperion

Saturn IV

Hyperion Facts

• Hyperion is the sixteenth of Saturn's known satellites:
  • distance from Saturn: 1,481,100 km
  • diameter: 286 km (410 x 260 x 220)
  • mass: 1.77e19 kg

• Pronounced "hi PEER ee en".

• In Greek mythology Hyperion was a Titan, the son of Gaea and Uranus and the father of Helios.

• Discovered by Bond and Lassell in 1848.

• Hyperion is the largest highly irregular (non-spherical) body in the solar system. Proteus is quite a bit larger but is almost spherical.

• 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.

• But unlike most of Saturn's moons, Hyperion has a low albedo (.2 - .3) indicating that it is covered by at least a thin layer of dark material. This may be material from Phoebe (which is much darker) that got past Iapetus.

• The Voyager images indicate that Hyperion's rotation is chaotic, i.e. its spin rate and orientation is completely unpredictable. More recent analysis, however, suggests that there may be a more regular 13 day rotation period.

• Hyperion's odd rotation may account 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.

Pictures

1. (above) Hyperion 8k gif; 20k gif; 5k jpg

2. Hyperion 7k gif

3. Hyperion, moon of Saturn, small image 134k gif
4. Hyperion, moon of Saturn, closer image 134k gif
5. Hyperion, moon of Saturn, closest image 116k gif

More about Hyperion

• from LANL

Open Issues

• Why is Hyperion's rotation so peculiar? Why is it not synchronously locked like the rest of Saturn's moons? Is it related to Hyperion's irregular shape?
• Hyperion's orbit is somewhat eccentric. Do the other small irregular moons (for which we have little or no data) with eccentric orbits also rotate chaotically?