Wanying Kang

This review synthesizes current knowledge of Enceladus as an Ocean World, with emphasis on habitability, organic chemistry, and the search for life. We summarize data obtained by the Cassini spacecraft, including the discovery and characterization of Enceladus’ plume and subsurface ocean. We assess how plume materials constrain the composition of the ocean, while highlighting uncertainties introduced by fractionation through transport and possible ice–ocean interface processes. We further examine how ocean dynamics and plume–ocean connectivity may shape the transport and transformation of dissolved and particulate species from the moon’s interior to space. We consider possible sources of chemical energy, redox disequilibria, and abiotic organic carbon, and how they could constrain ocean biomass, biological productivity, and the detectability of potential biosignatures. Finally, we evaluate near-term exploration strategies and mission architectures for testing theories of habitability, chemical evolution, and possible life beyond Earth.

The tiger stripes of Enceladus are a sequence of four parallel and evenly‐spaced fissures 130 km long that erupt water from a global subsurface ocean into space. We present an ocean dynamical theory of their formation. Given one initial fissure, topography on the underside of the ice shell rubs periodically against the ocean due to the satellite's libration. This motion excites internal gravito‐inertial waves that propagate downward and reflect at the seafloor before reimpacting the underside of the shell. Wave breaking upon impact generates thermal energy which promotes melting via a feedback mechanism, forming subsequent fissures in a chain of parallel stripes. Dissipation predicted by linear analytical theory matches nonlinear simulations using the MIT General Circulation Model, with stronger agreement when the topography is less steep. Sufficiently large topography and libration amplitude excite waves with enough energy to initiate the fissure formation process. For south polar ocean thickness between 30 and 60 km, we constrain the stratification ( ) at which the resulting wave pattern replicates the observed 35 km spacing of the tiger stripes.

Phys. Rev. Fluids 11, 079901 (2026)

A poleward‐thinning ice shell can drive circulation in the subsurface oceans of icy moons by imposing a meridional temperature gradient–colder at the equator than the pole–through the freezing point suppression due to pressure. This temperature gradient sets a buoyancy gradient, whose sign depends on the thermal expansion coefficient determined by ocean salinity. Together with vertical mixing, this buoyancy forcing shapes key oceanic features, including zonal currents in thermal wind balance, baroclinic instability of those currents, meridional heat transport by eddies, and vertical stratification. We use high‐resolution numerical simulations to explore how variations in ice shell thickness affect these processes. Our simulations span a wide range of topographic slopes, pole‐to‐equator temperature differences, and vertical mixing strengths, for both fresh and salty oceans. We find that baroclinic eddies dominate large‐scale circulation and meridional heat transport, consistent with studies assuming a flat ice‐ocean interface. However, sloped topography introduces new effects: when lighter water overlies denser water along the slope, circulation weakens as a stratified layer thickens beneath the poles. Conversely, when denser water lies beneath the poles, circulation strengthens as topography increases the available potential energy. We develop a scaling framework that predicts heat transport and stratification across all simulations. Applying this framework to Enceladus, Europa, and Titan, we infer ocean heat fluxes, stratification, and tidal energy dissipation, showing large‐scale circulation constrains tidal heating and links future observations of ice thickness and rotation to subsurface ocean dynamics.

Plumes that rise through an unstratified layer and penetrate into an adjacent stably stratified layer are ubiquitous in geophysical and planetary environments, including the subsurface oceans of icy satellites such as Europa, Enceladus, and Titan. In this study, we investigate the evolution of such plumes from isolated buoyant sources, both in non‐rotating and rotating systems, with particular emphasis on their penetration height. Non‐rotating plumes evolve into a classical “mushroom” structure, whereas rotating plumes evolve into baroclinic cones or can not reach the stratified layer, depending on the interface height . A scaling law for the penetration height is derived in terms of and two characteristic length scales, and , where is the buoyancy flux of the source, is the buoyancy frequency, and is the Coriolis parameter ( is the rotation rate). In the non‐rotating regime, the scaling recovers the classical relation when the unstratified layer is thin and predicts when the layer is thick. In the rapid‐rotating regime, remains constant for small , followed by a decrease toward zero as increases, due to the lateral mixing by baroclinic eddies. Under weak stratification, plumes typically arrest at about , independent of . Applying these scalings to icy‐ocean worlds suggests that on Europa, plumes could reach the ice shell, whereas on Enceladus and Titan, they are likely arrested in the mid‐ocean.

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 three-dimensional (3D) magma ocean dynamics, derives scaling laws for the resulting ocean heat transport, 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 ∼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 hot-spot offset. This inefficiency arises because basin geometry and circulation structure fundamentally constrain zonal heat redistribution, suppressing large-scale longitudinal transport even under vigorous flow.

It remains puzzling why, despite their similar nature, Jupiter and Saturn possess a prograde equatorial jet, whereas Uranus and Neptune have a retrograde one. To understand this discrepancy, we use a 2D quasi-geostrophic model to explore how the jet penetration depth, regulated by ohmic dissipation, influences the structure and organization of jet patterns. When jets penetrate deeply into the planetary interior, the effective planetary vorticity gradient β becomes negative near the equator and decreases equatorward due to spherical geometry. This β profile favors dynamical modes that transport eastward momentum toward the equator, producing a prograde equatorial jet, as observed on Jupiter and Saturn. In contrast, relatively shallow systems favor a retrograde equatorial jet. In our simulations, the equatorial jet direction is primarily controlled by the gradient of β , as predicted by stochastic structural stability theory, rather than by its sign, as suggested by potential vorticity mixing. If this mechanism applies to Uranus and Neptune, the observed jet structure may suggest the presence of a stratified or ohmic dissipation layer near their surfaces. At midlatitudes, jet widths are constrained by the Rhines scale, yielding a scaling that explains the presence of multiple jets on Jupiter and Saturn and a single jet per hemisphere on Uranus and Neptune. Lastly, we examine how planetary parameters influence the partitioning of energy between jets and eddies. Stronger energy input, faster rotation, smaller planetary radius, or weaker large-scale damping leads to a larger fraction of the total energy in zonal jets, resulting in smoother jet structures.