EXO-HEAT – Interior Heating of Exoplanets

Information on exoplanets is still sparse to date, but the data set is expanding fast due to the combined efforts of various telescopes. The next years will see a tremendous amount of new exoplanet detections and follow-up measurements to constrain planet properties and stellar data. Therefore, new techniques are needed now to help constrain the best planet candidates for expensive follow-up observations.

The atmosphere composition and structure depends on several different factors, such as chemical pathways in the atmosphere, reactions with the surface (e.g. carbonate formation), weathering effects, erosion to space and last, but definitely not least, replenishing of gases from the interior of the planet. One of the main factors that influences the amount of outgassing (and regassing) of volatiles (and hence greenhouse gases) is the energy available in the interior.

Since previous studies have already shown the effect that strong internal heating can have on factors such as plate tectonics (and hence recycling of volatiles into the interior), volcanic activity, and outgassing, here we rather address the fundamental question of how much heat can be expected in an exoplanet depending on its composition, interior thermal evolution (including loss of heat due to volcanic activity and plate tectonics cooling) and the available observational constraints that can be used to characterize a rocky planet’s thermal state. These observational constraints include the age of the system, the planetary mass and radius, the distance from the star and equilibrium surface temperature, the abundances of both major planet-building elements (Mg, Fe, Si) and radiogenic heat sources, but also external heat sources such as the magnetic field strength and orientation of the star (possibly leading to magnetic induction heating) and orbital configurations and related tidal dissipation.

In the past, studies typically either concentrated on single observational constraints (such as the surface temperature or the amount of tidal dissipation), or used general parameter studies to investigate the effect of single parameters (e.g. amount of radiogenic heat sources). Here, instead, we will combine all above mentioned observable constraints (as available for each individual planet) to investigate how different heat sources interact with each other (e.g. amplify their effect or reduce each other). This study is necessary to be able to better predict the range of interior evolution pathways. In the end, it is the heating in the interior that strongly influences the long-term evolution of the atmosphere and magnetic field and therefore the potential habitability of an exoplanet.