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Why are underground oceans on icy moons considered possible habitats for life?

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artist's conception of Kepler-186f — extraterrestrial intelligence An artist's conception depicts Kepler-186f, the first Earth-sized extrasolar planet found in its star's habitable zone.

Underground oceans on icy moons, such as Europa and Enceladus, are considered potential habitats for life because they provide stable environments that satisfy the fundamental requirements for biological existence.1

These subsurface oceans are maintained in a liquid state despite their distance from the Sun primarily through tidal energy generated by gravitational interactions with their host planets. This internal heating prevents the water from freezing solid, creating a long-lived reservoir of liquid water beneath an insulating icy crust.123

Furthermore, these environments may offer the chemical ingredients necessary for life. Evidence suggests that these oceans are in contact with rocky interiors, potentially allowing for hydrothermal vents that provide heat and minerals. The presence of organic molecules and other prebiotic chemicals on these moons further supports the possibility that they could sustain chemoautotrophic life-forms, which do not rely on sunlight for energy. Studies of similar extreme environments on Earth, such as Lake Vostok in Antarctica, serve as models for how life might survive in such isolated, subsurface conditions.3451