[Research Press Release] Astronomy: Boiling oceans and tectonic stresses reshape icy moons (Nature Astronomy)

Ice shell thinning on small icy satellites in the outer Solar System can cause subsurface oceans to boil, according to a modelling study published in Nature Astronomy. This process may help to explain surface features and geological activity on moons such as Saturn’s Mimas and Enceladus, and Uranus’s Miranda, and could influence future exploration strategies for ocean worlds.

Many moons in the outer Solar System host oceans beneath thick ice shells. Changes in ice shell thickness caused by orbital dynamics can alter ocean pressure and generate stress within the ice. While thickening shells have been linked to surface structures, including the tiger stripes that host eruptions of water and ice on Saturn's moon Enceladus, the effects of thinning ice shells are less well understood. Recent evidence suggests that some moons, including Mimas and Miranda, have experienced ice thinning, raising questions about the consequences for surface geology and internal dynamics.

Max Rudolph and colleagues modelled the evolution of ocean pressure and ice shell stresses during thinning phases for all of the mid-sized icy ocean worlds of the outer solar system. They found that on smaller bodies, such as Mimas (198 kilometre outer radius) and Enceladus (252 kilometre outer radius), ocean pressure can drop low enough to reach the triple point of water — the point at which solid, liquid, and gaseous water can exist simultaneously. This triggers boiling and evaporation before compressive failure of the ice shell occurs. Numerical simulations indicate that modest thinning of 5–15 kilometres can lead to boiling conditions. In contrast, larger moons (with a radius greater than 300 kilometres) such as Titania and Iapetus experience compressive failure first, producing faults that may account for the wrinkle ridges and equatorial tectonic features observed on their surfaces.

The findings suggest that boiling-driven processes could promote resurfacing and volcanic activity on small moons, while compressional tectonics may dominate larger ones. The findings could inform the future exploration of Enceladus or Uranus’s moons, which is considered a priority by NASA, the authors suggest.

• Article
• Published: 24 November 2025

Rudolph, M.L., Manga, M., Rhoden, A.R. et al. Boiling oceans and compressional tectonics on emerging ocean worlds. Nat Astron (2025). https://doi.org/10.1038/s41550-025-02713-5

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