ASU, Princeton scientists uncover surprising insights into habitability of super-Earths
Artist rendering of a volcanic exoplanet. Image courtesy of iStock/Getty Images
A recent study conducted by a collaboration of scientists from Arizona State University and Princeton University have discovered that super-Earths — rocky planets up to approximately five times the mass of Earth — may experience longer-lived volcanic activity and stronger magnetic fields for billions of years. These findings, published in the journal Science Advances, could have profound implications for the habitability of these distant worlds.
In June 2022, the James Webb Space Telescope (JWST) observed its first exoplanet with unique sensitivity and precision. Since then, researchers have observed in great detail gas giant atmospheres, hints about the properties of small, rocky exoplanets, and even how some exoplanets might have formed.
JWST’s observation of exoplanet TRAPPIST-1c revealed the lack of a thick carbon dioxide atmosphere, and while researchers can't say definitively, they are investigating hints of what could be a magnetic field around the potentially rocky exoplanet YZ Ceti b. Such findings are pushing the boundaries of our understanding of planetary atmospheres, magnetospheres and surface habitability.
Rocky planets, like Earth, generate geological phenomena such as volcanoes and magnetic fields by converting internal heat into dynamic processes. Super-Earths are a class of rocky planets absent in our solar system but common in the galaxy; they are similar to Earth in composition, but their mass can be much larger. The team of researchers, including Joseph O’Rourke, assistant professor at ASU’s School of Earth and Space Exploration, set out to understand thermal evolution of large rocky exoplanets and provide key insights into how the radioactive decay of elements deep within super-Earths drives planetary dynamics, potentially extending their habitability.
“Earth was born hot,” explains O’Rourke. “Its formation from the protoplanetary disk released enormous amounts of gravitational energy, alongside the impacts of large celestial bodies. Over billions of years, Earth has continued to generate heat through the decay of radioactive elements like potassium, uranium and thorium.”
Today, Earth gradually sheds its internal heat into space, driven comparably by the leftover heat of formation and the ongoing decay of radioactive elements concentrated in its rocky crust and mantle. This heat distribution is key to Earth's geological activity and the convection pattern in its mantle. But the big question remained: How does this change for super-Earths?
Surprising discovery: Heat-producing elements behave differently in super-Earths
Haiyang Luo and Jie Deng, researchers from Princeton University and co-authors of the study, tackled this question through extensive computational modeling. The researchers discovered that, under the immense pressures and temperatures of super-Earth interiors, key heat-producing elements transition from “lithophile” (rock-loving) to “siderophile” (iron-loving). This means that unlike Earth, where radioactive elements are concentrated in the rocky parts, the cores of super-Earths could become significant sources of heat, staying hot throughout a planet’s lifetime.
The team initially thought the location of heat production might not make much difference, but the team found that concentrating heat in the core leads to much longer-lived volcanism and planetary magnetism.
“The high pressures inside super-Earths force these radioactive elements into the core, fundamentally changing how heat is distributed throughout the planet," Luo said. "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.”
Impact on volcanism and magnetic fields
Using advanced numerical models, the research team found that this redistribution of heat dramatically impacts planetary evolution. A hot core sustains vigorous convection both in the mantle and the core, leading to enhanced geological activity.
This means that super-Earths are likely to experience prolonged surface volcanism and stronger, longer-lasting magnetic fields. These factors could have a significant effect on a planet’s habitability. Volcanism releases essential gasses into the atmosphere, while magnetic fields protect planets from harmful cosmic radiation.
Looking ahead: Implications for habitability
As astronomers continue to study exoplanetary atmospheres and magnetospheres, this recent study suggests that larger super-Earths may have the ingredients to support habitable environments for longer periods than Earth-sized planets.
“Our study opens the door to new possibilities in the search for life beyond our solar system,” said O’Rourke. “Although super-Earths might sustain life for longer, living on one would be incredibly difficult for humans due to their intense gravity."
The researchers emphasize the need for further sophisticated modeling of individual super-Earths to deepen our understanding of these fascinating worlds.
This research is an exciting leap forward in exoplanet studies, adding important insights into the dynamic processes that could make super-Earths prime candidates for habitability.
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