Abstract
The amount of detected planets with sizes comparable to that of the Earth is increasing drastically. Most of the Earth-size planet candidates orbit at close distances from their central star, and therefore are subjected to large tidal forces. Accurate determination of the tidal parameters of exoplanets taking into account their interior structure and rheology is essential to better constrain their rotational and orbital history, and hence their impact on climate stability and planetary habitability. In the present study, we compute the tidal response of rocky and ice-rich solid exoplanets for masses ranging between 0.1 and 10 Earth masses using a multilayer approach and an Andrade rheology. We show that the amplitude of tidal response, characterized by the gravitational Love number,k2, is mostly controlled by self-gravitation and increases as a function of planet mass. For rocky planets,k2depends mostly on the relative size of the iron core, and hence on the bulk iron fraction. For ice-rich planets, the presence of outer ice layers reduces the amplitude of tidal response compared to ice-free rocky planets of similar masses. For both types of planet (rocky and ice-rich), we propose relatively simple scaling laws to predict the potential Love number value as a function of radius, planet mass and composition. For the dissipation rate, characterized by theQ−1factor, we did not find any direct control by the planet mass. The dissipation rate is mostly sensitive to the forcing frequency and to the internal viscosity, which depends on the thermal evolution of the planet, which is in turn controlled by the planet mass and composition. The methodology described in the present study can be applied to any kind of solid planet and can be easily implemented into any thermal and orbital evolution code.
Highlights
The number of detected exoplanets with radius and mass comparable to that of the Earth is increasing drastically (e.g. Bonfils et al 2013; Batalha et al 2013; Marcy et al 2014; Dressing & Charbonneau 2015; Coughlin et al 2016; Dittmann et al 2017; Gillon et al 2017)
Most of the low-mass planet candidates orbit at relatively close distances from their central star and are likely subjected to large tidal forces due to the gravitational tide raised by the star
Accurate determination of the tidal parameters of exoplanets (k2 and Q) taking into account their interior structure and rheology is essential to better characterize their rotational and orbital history, which has a direct impact on their climate stability and habitability
Summary
The number of detected exoplanets with radius and mass comparable to that of the Earth is increasing drastically (e.g. Bonfils et al 2013; Batalha et al 2013; Marcy et al 2014; Dressing & Charbonneau 2015; Coughlin et al 2016; Dittmann et al 2017; Gillon et al 2017). We compute the tidal response of rocky and ice-rich solid exoplanets for masses ranging between 0.1 and 10 Earth masses using a multilayer approach and an Andrade rheology.
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