Geodynamos of Super-Earths

Abstract

Constraining the heat flow out of a planetary core over geological time remains a significant challenge, as the extreme pressures and temperatures involved push the limits of experimental capabilities. However, this heat flow is crucial for understanding planetary processes that are often linked to habitability in planetary sciences. A geodynamo driven by core cooling, mantle convection, and plate tectonics is strongly influenced by this value. Recent studies coupling higher-dimension visco-plastic mantle convection with core evolution models have demonstrated correlations for Earth, highlighting the need for more comprehensive models to explore these interactions in other rocky planets. One such potential correlation is between a planet’s surface magnetic field strength and its surface cooling regime, such as plate tectonics. Here, we present a new 2D mantle convection model coupled with a core evolution model, incorporating state-of-the-art equations of state for core and mantle minerals, to study the well-known exoplanet class: Super-Earths. Our results reveal a previously overlooked mechanism—an inner-core–mantle thermal feedback loop—emerging from our coupling approach. The Earth reference cases examined here further support the necessity of an additional geodynamo-driving mechanism in early Earth to resolve the "new core paradox". Additionally, we find that surface magnetic field intensities for super- Earths range from 25 to 360 μT. Notably, we observe that "hot" super-Earths (<3M⊕) exhibit geodynamo evolutions independent of surface regime, while those with a mobile lid (>3 M⊕) experience enhanced geodynamo lifetimes and stronger surface fields. This suggests a small but significant link for future observational detections.