Characterizing WASP-43b's interior structure: unveiling tidal decay and apsidal motion

Abstract

Kontext. Recent developments in exoplanetary research highlight the importance of Love numbers in understanding their internal dynamics, formation, migration history and their potential habitability. Love numbers represent crucial parameters that gauge how exoplanets respond to external forces such as tidal interactions and rotational effects. By measuring these responses, we can gain insights into the internal structure, composition, and density distribution of exoplanets. The rate of apsidal precession of a planetary orbit is directly linked to the second-order fluid Love number, thus we can gain valuable insights into the mass distribution of the planet. Aims. In this context, we aim to re-determine the orbital parameters of WASP-43b - in particular, orbital period, eccentricity, and argument of the periastron - and its orbital evolution. We study the outcomes of the tidal interaction with the host star: whether tidal decay and periastron precession are occurring in the system. Methods. We observed the system with HARPS, whose data we present for the first time, and we also analyse the newly acquired JWST full-phase light curve. We fit jointly archival and new radial velocity and transit and occultation mid-times, including tidal decay, periastron precession and long-term acceleration in the system. Results. We detected a tidal decay rate of 9Pa= (-1.99˘0.50) ms yr´1 and a periastron precession rate of 9ω=0.1727`0.0083´0.0089)˝ d´1 = (621.72 `29.88´32.04)2d´1. This is the first time that both periastron precession and tidal decay are simultaneously detected in an exoplanetary system. The observed tidal interactions can neither be explained by the tidal contribution to apsidal motion of a non-aligned stellar or planetary rotation axis nor by assuming non-synchronous rotation for the planet, and a value for the planetary Love number cannot be derived. Moreover, we exclude the presence of a second body - e.g. a distant companion star or a yet undiscovered planet -, down to a planetary mass of Á0.3 MJ and up to an orbital period of À 3 700 days. We leave the question of the cause of the observed apsidal motion open.