Definition
A hydrothermal moon is a natural satellite whose interior combines heat, ice, and liquid water, producing systems of hydrothermal circulation. These processes generally occur in environments where an icy crust covers an internal ocean in contact with a rocky or metallic core.
Internal Structure
The structure includes a solid core, often rocky, surrounded by a hydrated or partially aqueous mantle. Above lies an internal ocean kept liquid by internal heat and covered by an icy crust. Hydrothermal circulation develops at the interface between the core and the ocean, where water interacts with minerals.
Hydrothermal Circulation
Fluids penetrate cracks in the core, heat up upon contact with hot rocks, then rise into the ocean. This cycle transports chemical compounds, creates temperature gradients, and alters mineral composition. Internal hydrothermal vents are dynamic structures capable of producing deposits and redistributing energy.
Evolution
Hydrothermal activity varies depending on the amount of available heat, often sustained by tidal forces or internal radioactive decay. It may decrease or reorganize over time, altering the geometry of water reservoirs and the thickness of the surface ice.
Limitations
Hydrothermal systems are limited to zones where temperature and pressure allow the coexistence of liquid water and solid rocks. When heat decreases or the ocean freezes, hydrothermal circulation ceases, and the moon becomes primarily icy and inactive.