Interior heating by stellar magnetic fields as a driver of volcanic activity on massive rocky planets

We investigate possible driving mechanisms of volcanic activity on large rocky super-Earths with masses exceeding four Earth masses. Due to high pressures in the mantles of these planets, melting in deep mantle layers can be suppressed, even if the energy release due to tidal heating and radioactive decay is substantial in these areas of the mantles. We investigate if a newly identified heating mechanism, namely induction heating by the star’s magnetic field, can drive volcanic activity on these planets due to its unusual heating pattern close to the planet’s surface, which leads to heat production in the very upper part of the mantle. In this region the pressure is not yet high enough to preclude the melt formation. We use a model for induction heating we developed and apply it to the super-Earth HD 3167b, which has a mass of approximately seven Earth masses. We calculate induction heating in the planet’s interiors assuming an electrical conductivity profile of a hot rocky planet and a moderate stellar magnetic field typical of an old inactive star, which one can expect for HD 3167. Then, we use a mantle convection code (CHIC) to simulate the evolution of volcanic outgassing with time.

Fig. 1. Total outgassing of CO₂ , CO, H₂O, and H₂ from HD 3167b assuming the magnetic field of the star of 0, 1, and 5 G. Induction heating leads to a much earlier onset of volcanism on the planet and increases the outgassing by several tens of bar. The mantle viscosity is 10 times the mantle viscosity of the Earth.

According to our results, in most cases volcanic outgassing on HD 3167b is not very significant in the absence of induction heating, however, including this heating mechanism changes the picture and leads to a substantial increase in the outgassing from the planet’s mantle. Evolution of volcanic outgassing is illustrated in Fig. 1. Induction heating also leads to a much earlier onset of volcanic activity on this planet. This result shows that induction heating combined with a high surface temperature is capable of driving volcanism on massive super-Earths, which has very important observational implications.