Last update: October 4, 2025

Saturn's Moons: Icy Worlds and Hidden Oceans

Satellites with extreme characteristics

With 146 confirmed moons as of 2025 (24 of which are still awaiting official names), Saturn holds the solar system record for the diversity of its natural satellites. These celestial bodies, ranging in size from a few hundred meters to over 5,000 km for Titan, offer a unique laboratory for studying geological processes and exobiological potential beyond Earth.

Data collected by the Cassini-Huygens mission (1997-2017) revealed surprising landscapes:

Lakes of liquid hydrocarbons on Titan
Geysers of salty water vapor on Enceladus, evidence of a global subsurface ocean
Giant craters like Herschel on Mimas, giving it the appearance of the Death Star
Fractured surfaces like that of Dione, evidence of past tectonic activity

Titan: A prebiotic world?

With a diameter of 5,151 km (larger than Mercury), Titan is the only moon in the solar system with a dense atmosphere (1.5 times Earth's pressure), composed of 95% nitrogen. Radar observations have confirmed the presence of seas of liquid methane and ethane, as noted by Carolyn Porco (1953-): "Titan is the most Earth-like world we have found, but with exotic chemistry where methane plays the role of water." Climate models suggest a complex seasonal cycle where methane rains carve river networks similar to those on Earth, but at average temperatures of -179°C.

Enceladus: A habitable ocean?

Flybys of Enceladus (504 km in diameter) revealed plumes rich in nanocrystalline silica, molecular hydrogen, and organic compounds. According to a study published in Science (2017) by Hunter Waite (1959-), these elements suggest active hydrothermal vents at the bottom of its subsurface ocean, similar to those that host life on Earth near ocean ridges.

The Cassini probe measured a heat flow of 15.8 ± 3.1 GW at the south pole, 2.6 times the energy produced by all of Earth's hydrothermal vents. This energy, combined with the presence of ammonia (which acts as antifreeze), maintains a global ocean 26 to 31 km thick beneath an ice crust 20 to 25 km thick.

Saturn's main moons: Witnesses to the formation of the Solar System

Comparison of Saturn's main moons
Moon	Diameter (km)	Distance from Saturn (km)	Major characteristic	Habitability index (0-1)	Discovery (year)
Titan	5,151	1,221,870	Dense atmosphere (95% N₂) + liquid methane/ethane lakes + seasonal cycles	0.64	1655
Enceladus	504	237,948	Active geysers (200 kg/s vaporization) + global ocean (26-31 km deep) + confirmed hydrothermal activity	0.78	1789
Rhea	1,528	527,108	Ancient, cratered surface (temperature: -174°C) + possible tenuous ring system	0.12	1672
Dione	1,123	377,415	Tectonic fractures (chasmata) + possible subsurface ocean (detected by Cassini in 2016)	0.35	1684
Iapetus	1,470	3,560,820	Hemispheric dichotomy (albedo 0.03-0.6) + equatorial ridge (20 km high)	0.08	1671
Tethys	1,062	294,619	Large Odysseus crater (400 km) + Ithaca Chasma canyon (100 km wide)	0.21	1684
Mimas	396	185,539	Herschel crater (130 km, 1/3 of diameter) + orbital resonance with Enceladus	0.05	1789
Hyperion	270	1,481,100	Irregular shape (sponge-like) + chaotic rotation + CO₂ ice-rich composition	0.03	1848
Phoebe	213	12,944,300	Probable origin in the Kuiper Belt + retrograde orbit + dark surface (albedo 0.06)	0.01	1899
Enceladus (south pole)	-	-	Local temperature: -93°C (vs -198°C elsewhere) + 101 identified geysers	0.85 (specific area)	-

Challenges of future exploration

Three missions are under development to study these moons:

Dragonfly (NASA, launch planned for 2028): nuclear-powered drone to explore Titan
Enceladus Orbilander (proposed NASA mission): orbiter + lander to analyze plumes
MMX (JAXA, 2026): study of Martian moons but with adaptable instruments

Analysis of returned samples could answer the question posed by Carl Sagan (1934-1996): "Are we alone in the universe?" The subsurface oceans of these moons are indeed the most promising environments for finding extraterrestrial microbial life in our solar system.