Enceladus

Enceladus is a small icy moon of the planet Saturn. With a mean diameter of about 504 kilometers, it is one of the mid-sized moons in Saturn’s system. It orbits Saturn in a near-equatorial, prograde orbit at an average distance of about 238,000 kilometers, completing an orbital period of roughly 1.37 days. The moon was discovered by William Herschel in 1789 and is named after a Titan from Greek mythology.

Enceladus has a highly reflective surface and is dominated by clean water ice. The south polar region hosts a set of tectonically controlled fissures known as the tiger stripes: Damascus Sulcus, Baghdad Sulcus, Cairo Sulcus, and Alexandria Sulcus. These fractures are the source of persistent plumes that eject water vapor, ice grains, and traces of salts and organic compounds into space. The plumes feed Saturn’s E ring and have provided a direct glimpse into subsurface activity.

Data from the Cassini–Huygens mission in 2005 revealed the plumes and indicated the existence of a subsurface liquid water reservoir, or ocean, beneath an icy crust. Gravitational and magnetic measurements suggest the ocean remains in contact with a rocky core, likely heated by tidal forces due to Enceladus’s resonance with Dione. The combination of liquid water, organics, and energy sources makes Enceladus a prime example of a potentially habitable icy world in the outer solar system.