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MOON

Hyperion

The chaotic sponge-moon — an irregular, porous body that tumbles unpredictably.

Orbits Saturn

One of only two irregularly shaped moons known to rotate chaotically (along with Saturn's Phoebe).
Sponge-like appearance from extremely high porosity (~40%).
No predictable day u2014 rotation is mathematically chaotic due to tidal resonance with Titan.

Physical Properties

Mean radius135 km

Mass5.6199e18 kg

Density0.544 g/cm³

Bond albedo0.3

Mean temp93 K

Orbit

OrbitsSaturn

Semi-major axis1,481,009 km

Eccentricity0.123

Inclination0.43°

Orbital period21.276 d

Missions to Hyperion

1 spacecraft tracked on Space Launch Live.

Sources & Further Reading

Numerical values (radius, mass, orbital elements, temperatures) are drawn from NASA NSSDC Planetary Fact Sheets, JPL Horizons, and the JPL Small-Body Database. Last refreshed: 2026-04-18 18:19:24.

Hyperion is an irregularly shaped, heavily pitted moon of Saturn with an unusual “sponge-like” appearance caused by a very high bulk porosity — around 40%, the lowest density of any major moon. Its rotation is mathematically chaotic: tidal torques from Saturn and its orbital resonance with the much larger Titan produce a tumble that never repeats, making it one of only two non-synchronously-rotating moons whose attitude cannot be long-term predicted.