Mantle rheology, internal dynamics and tidal heating of massive rocky exoplanets

Kurzfassung

The pressure dependence of mantle rheology is often not taken into account when dealing with rocky exoplanet interiors due to limited knowledge about the rheological properties of silicate perovskite and post-perovskite at a high degree of compression [1]. In this talk, I will use the Kepler-36b exoplanet [2] as a case study to examine the rheological and thermal structure inside of massive rocky planets. Particular emphasis will be placed on addressing the question of how the present thermal structure and tidal heating rates are affected by a mantle rheology dominated by silicate post-perovskite. I will show that the mantle viscosity depends weakly on planetary mass owing to a viscosity-temperature feedback mechanism (e.g., [3], [4]). Furthermore, a super-adiabatic temperature gradient in the deep interior ([3], [5]) implies substantially higher core and mantle temperatures than previously reported from parameterized convection models (e.g., [6]). This has implications for the possible existence of a self-sustained magnetic field in rocky exoplanets that will be discussed. I will also discuss how tidal dissipation rates of rocky exoplanets are affected by the obtained rheological structure by calculating body tide potential Love numbers for different visco-elastic rheological models. [1] Karato 2011: Rheological Structure of the Mantle of a super-Earth: Some Insights from Mineral Physics. Icarus 212, 14-23. [2] Carter et al. 2012: Kepler-36: A Pair of Planets with Neighboring Orbits and Dissimilar Densities. Science 337, 556-559. [3] Wagner et al. 2011: Interior Structure Models of Solid Exoplanets using Material Laws in the Infinite Pressure Limit. Icarus 214, 366-376. [4] Tackley et al. 2013: Mantle Dynamics in super-Earths: Post-perovskite Rheology and Self-regulation of viscosity. Icarus 225, 50-61. [5] Wagner et al. 2012: Rocky super-Earth Interiors: Structure and Internal Dynamics of CoRoT-7b and Kepler-10b. A&A 541, A103-A116. [6] Valencia et al. 2006: Internal Structure of Massive Terrestrial Planets. Icarus 181, 545-554.