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Parameter Space Exploration of Low-to-moderate-temperature Hydrothermal Systems on Ocean Worlds Using a Monte Carlo Framework

Parameter Space Exploration of Low-to-moderate-temperature Hydrothermal Systems on Ocean Worlds Using a Monte Carlo Framework

Habitable Zones

Status Report

The Planetary Science Journal

September 5, 2025

Parameter Space Exploration of Low-to-moderate-temperature Hydrothermal Systems on Ocean Worlds Using a Monte Carlo Framework — Diagrams illustrating the conceptual and theoretical basis for coupled fluid-heat calculations shown in this study, as may apply to an ocean world (variables discussed in text and defined in Table A1). (a) The cartoon shows a two-dimensional slice through a three-dimensional flow system, with depth profile oriented parallel to net fluid transport within a hydrothermal siphon and fluid entering and exiting the seafloor through permeable channels (presented here as “outcrops” but could be fractures or other heterogeneities in properties). A porous and saturated aquifer below the seafloor is heated from below, with buoyant fluid consequently discharging through one outcrop and recharging through another. Cartoon adapted from A. Fisher & R. Harris (2010). (b) Examples of thermal profiles at the discharge side of the siphon comparing conductive conditions (no flow; green dashed line) with rapid isothermal upflow (solid red line) and slower, less rapid upflow (orange dashed curve) during which fluid partly cools during ascent. Similar profiles occur at the recharge site but with maximum curvature at the base. (c) Top-down perspective view of flow between recharging and discharging sites (blue and red, respectively), forming a geothermal dipole that functions as a heat exchanger between the fluid and silicate solid body. — The Planetary Science Journal

We explore the hydrogeologic and physical conditions necessary to sustain hydrothermal activity within the shallow subseafloors of ocean worlds, exploring wide ranges of multiple parameters using a Monte Carlo framework.

We apply multiple analytical calculations to represent coupled fluid-thermal flow systems, as have been observed on Earth, using idealized representations that link lateral transport below a conductive boundary layer between sites of hydrothermal inflow (recharge) and outflow (discharge).

These analytical calculations replicate outcomes and trends in results generated from more complex numerical simulations once we account for excess driving pressure that is consumed by secondary (local) convection during transport within the subseafloor.

We investigate low heat flux scenarios that are expected to be limiting cases for sustaining hydrothermal flows (≤10 mW m⁻²) for which there is modest heating from radiometric decay and/or tidal dissipation within the interior of an ocean world.

We explore limiting conditions appropriate for Europa’s deep subseafloor, and a subset of sustainable hydrothermal siphon calculations are identified that are especially efficient for mining interior heat. We identify parameters that can sustain a hydrothermal siphon for reaction temperatures of 80°C–120°C and water/rock mass ratios of ≤100 Gy^–1.

These conditions should result in discharging fluids that are altered relative to inflowing water and a silicate interior that is more likely to retain the potential for geochemical reactions over geologic time. These conditions are of particular interest because they could help create habitable conditions below or at the seafloor of an ocean world and can provide a foundation for linked reaction modeling.

Parameter Space Exploration of Low-to-moderate-temperature Hydrothermal Systems on Ocean Worlds Using a Monte Carlo Framework, The Planetary Science Journal (open access)
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