Hot Jupiters are spiralling into their stars faster than expected, and the reason may lie in how tidal forces churn the insides of planets and stars. This project tackles a fundamental gap in astrophysics: why tidal dissipation—the process that drains orbital energy into heat inside a star or planet—remains poorly understood despite its central role in shaping planetary systems. Current models cannot explain observed orbital decay rates, the spin-up of host stars, or why some stellar orbits are circular while others are not. The researchers will run the first global simulations that combine realistic differential rotation (like the Sun’s equatorial spin) and magnetic fields to model tidal flows inside stars and giant planets. If successful, the work will produce publicly available, physically grounded computer codes that predict how tides evolve in exoplanet systems and binary stars. These tools will help interpret data from upcoming missions such as PLATO, launching in 2026. The research is fundamentally curiosity-driven—it asks how stars and planetary systems develop—but the results could eventually inform models of planetary habitability by revealing which orbits remain stable over billions of years.
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Gravitational tidal interactions play crucial roles in the formation and evolution of planetary systems and binary stars. There is exciting new evidence for: tidally-induced orbital decay of hot Jupiters, including WASP-12b and Kepler-1658b, tidally-driven spin-up of planetary host stars, and tidal evolution of the distribution of stellar obliquities. The circularisation periods (essentially the maximum orbital period for which orbits are primarily circular) of hot Jupiters and close binary stars of various spectral types are thought to be explained by dissipation of tidal flows excited inside planets and stars. The mechanisms of tidal dissipation remain poorly understood however, despite their key roles in driving dynamical evolution and in the interpretation of current and future observations in these systems from e.g. WASP, NGTS, TESS and PLATO (ESA-funded with significant UK contributions, launching in 2026). We shall use numerical simulations from first principles to tackle the following key questions: (a) How does realistic differential rotation modify excitation and dissipation of tidal waves in stars and giant planets? (b) How do realistic magnetic fields affect tidal dissipation in stars and planets? Our results will be used to construct simplified, physically-motivated parametrisations of tidal processes for modelling observations. We will make these ready-to-run codes publicly available on GitHub so they can be incorporated in planetary and stellar population synthesis models. This project comes under STFC’s Science Challenge B (also a scientific priority of ASTRONET 2022-2035): How do stars and planetary systems develop and how do they support the existence of life? We will undertake the first global linear and nonlinear magneto-hydrodynamical (MHD) simulations of tidal flows in convection zones of planets and stars with realistic differential rotation (e.g. as observed for the solar convective envelope and Jupiter's atmosphere), density, and global magnetic field configurations, to understand dissipation of tidal waves in these bodies. This project will significantly advance our understanding of tidal dissipation in stars and planets, allowing us to make predictions for exoplanet systems and stellar binaries during the early stages of the PLATO mission. Our research is internationally unique and distinct in that we primarily undertake simulations from first principles, by directly solving the governing MHD equations. Our approach complements the tidal theory being developed elsewhere, and the results we obtain will guide our construction of new physically-motivated parametrisations that we will use (and publish for the community) for modelling observations.
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