Silica at Enceladus is an ambiguous sign of seafloor hydrothermal activity

Icy moons of the outer solar system, such as Europa and Enceladus, harbor global oceans in contact with their silicate interiors1. This makes them ideal targets in the search for subseafloor water-rock interactions that could release sufficient chemical energy to support life2. However, positive detection and identification of such hydrothermal systems, which remain theoretical, is challenging due to tens of kilometers of ice and ocean. Silicon detected in stream particles leaving the Saturnian system3 has previously been proposed to be the remnants of silica nanoparticles formed at hydrothermal vents on Enceladus4. If correct, this would be the first chemical evidence of an active seafloor hydrothermal system outside of Earth. In this work, we combine large-scale chemical equilibrium modeling with dynamical fluid simulations to investigate the plausibility of that hypothesis. We evaluate co-occurring physical and chemical processes that must operate within the ocean of Enceladus if hydrothermally-sourced Si nanoparticles are to survive within the ocean long enough to transit from the seafloor to the ice-ocean interface. While this does not preclude the habitability of Enceladus, we find that even if silica nanoparticles form near the seafloor of Enceladus they will dissolve within months unless they are somehow protected from dissolution. The ocean circulation patterns that transport Si nanoparticles (absent vertical transport in association, for example, with gas bubbles) would take more than a century to carry them from the seafloor to the ice-ocean interface. We conclude that the silicon detected by Cassini among particles in the E-ring of Saturn is unlikely to be evidence of seafloor hydrothermal processes, and may, instead, be evidence of particles formed near the ice-ocean interface, akin to particles found at marine ice-ocean interfaces on Earth.