Three-Dimensional Ocean Dynamics and Detectability of Tidally Locked Lava Worlds

TL;DR

This study models 3D magma-ocean dynamics on tidally locked lava planets, revealing wind-driven circulation dominates but does not cause observable hotspot offsets due to geometric constraints.

Contribution

It introduces the first consideration of wind-driven ocean circulation in magma-ocean dynamics and derives scaling laws for ocean heat transport on lava worlds.

Findings

Wind forcing drives ocean currents up to 100 m/s.

Ocean circulation does not produce observable hotspot offsets.

Basin geometry constrains large-scale heat redistribution.

Abstract

Tidally locked lava planets are hot, rocky worlds on close-in orbits with a permanent molten dayside. With JWST, their surfaces and atmospheres are beginning to be revealed. This work investigates 3D magma-ocean dynamics, derives scaling laws for the resulting ocean heat transport (OHT), and predicts its detectability. For the first time, the ocean circulation driven by the intense momentum and mass exchanges with the supersonic atmosphere is considered in addition to that by thermal forcing. The wind forcing turns out to overwhelmingly dominate the other two mechanisms, driving ocean currents reaching $\sim$100 m s$^{-1}$ and greatly expanding the latitudinal extent of the Matsuno-Gill response. Despite these extreme flow speeds, scaling analysis and 3D simulations consistently demonstrate that magma-ocean circulation alone does not produce an observable hotspot offset. This inefficiency arises because basin geometry and circulation structure fundamentally constrain zonal heat redistribution, suppressing large-scale longitudinal transport even under vigorous flow.