Enceladus (moon)

Enceladus is a moon of Saturn discovered in 1789 by William Herschel.

At least five different types of terrain have been identified on Enceladus. In addition to craters there are smooth plains and extensive linear cracks and ridges. At least some of the surface is relatively young, probably less than 100 million years. This means that Enceladus must have been active very recently with some sort of "water volcanism" or other process that renews the surface. The fresh, clean ice that dominates its surface gives Enceladus the highest albedo of any body in the solar system (Visual geometric albedo of 0.99). Because it reflects so much sunlight, the mean surface temperature is only -201°C.

Enceladus is much too small to be heated by the decay of radioactive material in its interior at present. Enceladus is locked in a 1:2 orbital resonance with Dione, similar to the situation between Io and Europa, and this may provide a tidal heating mechanism; however it is probably insufficient to melt water ice. Enceladus may therefore be composed of some low-melting point material instead of pure water. There are fissures, plains, corrugated terrain and other crustal deformations that indicates the interior of the moon may be liquid today, even though it should have frozen aeons ago.

Enceladus may be the source of the material in Saturn's tenuous E ring, and since the material cannot persist in the ring for more than a few thousand years it may be due to very recent activity on Enceladus. Another possibility, though, is that the rings are maintained by high-velocity collisions between dust particles and the various moons.