Impact of Heat-Producing Elements in the Core on Super-Earth Evolution and Dynamics

Radiogenic heating plays a crucial role in shaping a planet’s evolution and dynamics. On Earth, ~50% of surface heat loss originates from the decay of three long-lived, heat-producing elements (HPEs): potassium, thorium, and uranium. These elements are strongly lithophile and preferentially concentrate in the silicate mantle of planets. However, a recent study by Luo et al. (Science Advances, 2024) suggests that under the high-pressure, high-temperature conditions of core formation in large rocky planets (so-called super-Earths), these HPEs may become siderophile, partitioning preferentially into the iron core. The presence of HPEs in the mantles of super-Earths plays a crucial role in their internal dynamics. A feedback loop between internal heating, temperature, and viscosity regulates mantle temperature, adjusting viscosity to the value needed to facilitate convective loss of the radiogenic heat (Tackley et al., Icarus 2013). However, if these sources of radiogenic heat partition into the core, mantle convection in super-Earths becomes dominated by heat flowing from the core rather than by a mix of internal heating and cooling from above (as in Earth). Using 1D, parameterized mantle evolution models, Luo et al. (Science Advances, 2024) show that this shift leads to a sharp rise in core-mantle boundary (CMB) temperatures and an increase in total CMB heat flow, with significant implications for volcanism and magnetic field generation.

In this study, we perform mantle convection simulations using the StagYY code (Tackley, PEPI 2008), extending the models of Tackley et al. (Icarus, 2013) to include HPEs in the core, as suggested by Luo et al. (Science Advances, 2024). Our models are run in a 2D spherical annulus geometry and allow for melting at all mantle depths. We test different planetary masses, from 1 to 10 Earth masses, as well as different post-perovskite rheologies, (upper- and lower-bound, following Tackley et al. 2013, and interstitial rheology following Karato 2011), two tectonic regimes (stagnant and mobile-lid), and three mantle-to-core partitioning ratios of HPEs (0.1, 1, and 10). This work contributes to the growing understanding of the interior dynamics of super-Earths, and their implications on surface and atmospheric conditions, the presence of a magnetic field, and habitability potential.