Princeton, NJ – A new study led by scientists at Princeton University reveals how the internal heat of super-Earths—rocky planets up to six times the mass of Earth—can sustain volcanic activity and magnetic fields for billions of years. This research, published in Science Advances, challenges long-standing assumptions about the thermal evolution of large rocky exoplanets and provides key insights into how the radioactive decay of elements deep within super-Earths drives planetary dynamics, potentially extending their habitability. 

Moving Beyond Discovery: Characterizing Exoplanets in New Ways 

As we enter the era of exoplanet characterization, we are no longer limited to just discovering these distant worlds. Recent breakthroughs, such as those from the James Webb Space Telescope (JWST), have provided more detailed observations of exoplanets, like the discovery that TRAPPIST-1c lacks a thick carbon dioxide atmosphere, and the identification of a probable magnetic field around the rocky exoplanet YZ Ceti b. These results are pushing the boundaries of our understanding of planetary atmospheres, magnetospheres, and surface habitability. “Magnetic fields and volcanism, driven by the planet’s internal heat, are crucial to maintaining habitable environments. Volcanic outgassing contributes to the formation and maintenance of atmospheres, while magnetic fields shield the surface from harmful cosmic radiation. The new study presents a fundamental discovery about how radioactive elements—key contributors to a planet’s internal heat budget—behave under the extreme conditions inside super-Earths,” said Jie Deng, the study’s principal investigator and an assistant professor of geophysics at Princeton. 

Key Discoveries: Super-Earths' Cores as Furnaces

On Earth, roughly half of the heat escaping from the surface originates from the decay of long-lived radioactive isotopes of potassium, thorium, and uranium, which are concentrated in the crust and mantle. It has long been assumed that these elements remain in the rocky parts of the planet, even for large exoplanets like super-Earths. However, under the extreme pressures and temperatures found in super-Earths, these heat-producing elements become "siderophile" (iron-loving), sinking into the metallic core rather than staying in the silicate mantle. Haiyang Luo, the paper’s lead author and a postdoctoral associate at Princeton, added: “The high pressures inside super-Earths force these radioactive elements into the core, fundamentally changing how heat is distributed throughout the planet. Our findings show that the core of a super-Earth can store vast amounts of radioactive heat. The siderophile behavior of heat-producing elements under high pressure is a fundamental result that requires rethinking the thermal evolution models of large rocky planets.” 

A New Perspective on Super-Earth Evolution and Habitability 

This discovery has profound implications for understanding the evolution and potential habitability of super-Earths. Joseph G. O’Rourke, a co-author from Arizona State University, helped run numerical models to understand how this shift in heat distribution affects the planets’ geologic and magnetic activity. Conventional models assumed that internal heating from the mantle drove geologic activity, but the new results suggest that heat from the core plays a dominant role in driving mantle convection, whether the planet operates with plate tectonics or in a stagnant-lid regime. The study shows that super-Earths may have much longer geological and magnetic lifetimes than previously thought. A hotter, longer-lived core means stronger convection, prolonged volcanic activity, and a persistent magnetic field—key factors in maintaining a stable, life-supporting environment over time. If these planets develop habitable conditions early in their history, they may be able to sustain those conditions throughout the entire main-sequence lifetimes of Sun-like stars. This finding opens new avenues for predicting the habitability of terrestrial exoplanets. Future exoplanet studies will need to consider the core as a significant driver of planetary dynamics, reshaping our understanding of which exoplanets may be capable of supporting life.

Luo, H., J. G. O’Rourke, Deng, J., Radiogenic heating sustains long-lived volcanism and magnetic dynamos in super-Earths, Science Advances, 2024. DOI: 10.1126/sciadv.ado7603