Enceladus is a small, dazzlingly white moon that turned out to be one of the most promising places to look for life beyond Earth. Fractures at its south pole - the “tiger stripes” - continuously jet water from a salty ocean hidden beneath the ice, and that sprayed-out snow spreads into Saturn’s diffuse E ring.
Over 100 geysers erupt from the four “tiger stripe” fractures at its south pole.
Its fresh ice reflects ~99% of incoming sunlight - the most reflective body in the Solar System.
Snow falling back from the plumes keeps its surface bright and feeds Saturn’s E ring.
A free sample of an alien ocean
Normally you would drill through kilometres of ice to reach a subsurface ocean. Enceladus does the work for us: its geysers launch ocean water straight into space. Cassini flew through the plume and found salts, silica grains and hydrogen - chemistry that points to hot hydrothermal vents on the seafloor, the same kind of setting where life on Earth may have begun.
Physical characteristics
Diameter
504 km
Mass
1.080e+20 kg
Surface gravity
0.11 m/s²
Density
1.61 g/cm³
Tidally locked
Yes
Mean temperature
-201 °C
Geometric albedo
0.99
Atmosphere and composition
Atmosphere
None globally - but the south-polar water plumes form a thin, localised envelope of vapour.
Composition
A water-ice shell over a global salty ocean and a rocky core.
Interior structure
Porous rocky coremodelled
Water likely circulates through the hot porous rock - hydrothermal vents.
Global water oceanobserved
Confirmed by the moon’s measured wobble - the shell floats free of the core.
Ice shellobserved
A few km thin at the south pole, where geysers vent the ocean to space.
How we know: Cassini flew through the south-polar geysers and tasted salty ocean water directly; the libration measurement proved the ocean is global. The core structure is modelled.
Discovery
Discovered by
William Herschel
Year
1789
How
His 40-foot reflector telescope
Missions
Voyager 2NASA · Flyby probe · 1977 · active
Launched 16 days before its twin, Voyager 2 is the only spacecraft ever to visit all four giant planets - Jupiter, Saturn, Uranus and Neptune. It entered interstellar space in 2018 and is still returning data.
Cassini orbited Saturn for 13 years, delivering ESA’s Huygens probe to the surface of Titan in January 2005 - the first landing in the outer Solar System. It ended with a deliberate plunge into Saturn in 2017 to protect the potentially habitable moons Enceladus and Titan.