Limited direct fluid exchange between the deep subsurface ocean and the shallow subsurface environment of Europa

Abstract

Numerous icy moons, including Europa, possess subsurface oceans beneath their icy exteriors. Liquid water from Europa’s deep ocean has been proposed to rise through dykes and form shallow sills. Such reservoirs could create transient habitable environments and may be directly linked to the formation of various surface features on Europa. However, whether dykes can transport enough water from Europa’s deep ocean to form these shallow reservoirs remains poorly constrained. Here we couple high-resolution laminar and turbulent fluid–thermal simulations to test this mechanism. We first show that, even when we completely neglect convective heat losses, thus providing an upper-bound estimate, the volume of water capable of ascending through dykes before freezing is insufficient to account for the hypothesized surface features. We then show that turbulence notably strengthens this limitation by enhancing heat loss, driving rapid supercooling, promoting frazil ice formation and accelerating dyke clogging. Our results suggest that direct fluid exchange between Europa’s deep ocean and shallow subsurface is minimal and that in situ melting may be the primary source of any shallow liquid water, if present. Notably, this also implies that shallow liquid reservoirs, if encountered by future missions, may not truly reflect the geochemical signature of the underlying ocean.