Star-Planet Interactions: A Computational View

TL;DR

This paper reviews the use of three-dimensional numerical models to understand star-planet interactions, emphasizing the importance of combining observations with simulations to interpret physical phenomena and system properties.

Contribution

It highlights the critical role of 3D models in interpreting star-planet interactions and advocates for integrating multi-wavelength observations to enhance understanding.

Findings

Models are essential for interpreting observations.

Non-axisymmetric forces create asymmetric features.

Interactions vary over multiple timescales.

Abstract

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 through the lens of three-dimensional (3D) numerical models. The main conclusions are: * 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 non-axisymmetric forces of the interactions generate spatially asymmetric features (e.g., planetary material trailing the orbit, shock formation), thus requiring the use of 3D models. * Star-planet interactions vary in different timescales (from hours to giga-years) that are related to both planetary (orbital motion, rotation) and stellar (flares, cycles, and long-term evolution) properties. Understanding these variations require time-dependent models. I advocate that future 3D models should be informed by multi-wavelength, (near-)simultaneous observations. The use of observations is twofold: some generate inputs for models (eg stellar magnetic field maps), whereas others are fitted by models (eg spectroscopic transits). This combination of observations and models provides a powerful tool to derive physical properties of the system that would otherwise remain unknown.