Star–Planet Interactions: A Computational View

There are several physical processes that mediate the interaction between an exoplanet and its host star, with the four main ones being due to magnetic, particle (stellar outflow), radiative, and tidal interactions. These interactions can be observed at different wavelengths, from X-ray to radio. Their strengths depend on the architecture of planetary systems, as well as the age and activity level of the host stars. In particular, exoplanets in close-in orbits and/or orbiting active host stars can experience strong physical interactions, some of which are negligible or absent in the present-day Solar System planets. Here, I present an overview of star–planet interactions (SPIs) through the lens of three-dimensional (3D) numerical models. The main conclusions are as follows: ▪ Models are fundamental to interpret and guide observations. The powerful combination of observations and models allows us to extract important physical parameters of the system, such as planetary magnetic fields, stellar wind properties, etc. ▪ The nonaxisymmetric forces of the interactions generate spatially asymmetric features (e.g., planetary material trailing the orbit, shock formation), thus requiring the use of 3D models. ▪ SPIs vary in different timescales (from hours to gigayears) that are related to both planetary (orbital motion, rotation) and stellar (flares, cycles, and long-term evolution) properties. Understanding these variations requires time-dependent models. I advocate that future 3D models should be informed by multiwavelength, (near-)simultaneous observations. The use of observations is twofold: some generate inputs for models (e.g., stellar magnetic field maps), whereas others are fitted by models (e.g., spectroscopic transits). This combination of observations and models provides a powerful tool to derive physical properties of the system that would otherwise remain unknown.