Irregular moon of SaturnA sponge-shaped world

Hyperion

Hyperion is a jumbled, porous moon whose irregular shape and chaotic rotation refuse to behave like most satellites.

Moon of Saturn · about 270 km mean diameter · 21.28-day orbit · chaotic rotation

Host: Saturn
Type: Irregular icy moon
Mean diameter: About 270 km
Mean orbital radius: 1,481,100 km
Orbital period: 21.28 days
Rotation: Chaotic
Density: Unusually low
Discovered: 1848 · William Bond and George Bond

Hyperion up close

NASA imagery

Enhanced-colour Cassini view of Saturn's sponge-like moon Hyperion — **Multicolour Hyperion** Cassini's enhanced-colour view highlights Hyperion's deep pits and jumbled terrain. The moon may be more than one-third empty space. Image: NASA/JPL/Space Science Institute.

Porosity and pits

Hyperion's low density implies a highly porous interior: a rubble-rich body with substantial empty space between its fragments. Its surface is covered in sharp-rimmed pits rather than ordinary fresh craters.

Dark material fills the bottoms of many depressions. This may be dust rich in organic compounds, perhaps inherited from elsewhere in the Saturnian system.

Tumbling through orbit

Hyperion does not rotate predictably. Its irregular shape and gravitational interaction with Titan leave it tumbling chaotically, with its spin orientation changing over time.

The moon resides just outside a 4:3 orbital resonance with Titan. That resonance may have driven the breakup of an earlier moon, supplying Hyperion with debris or contributing to its irregular structure.

Worth knowing

Hyperion has one of the most unusual rotations of any Solar System moon.
Its density is roughly half that of water ice, largely because of internal porosity.
It was discovered independently by two teams on the same night in 1848.

Watch and explore

Research & further reading

Mission imagery and measurements are interpreted alongside orbital data. Follow the source links for the current NASA overview and precise satellite parameters.

Mission reference NASA · Hyperion ↗ NASA's overview of Hyperion and its exploration. Orbital data NASA/JPL satellite elements ↗ Mean orbital elements and current satellite catalogue data.