Super-Earths Not so Big on Life

Artist's impression of the trio of super-Earths discovered using the European Southern Observatory's 3.6-m telescope after five years of monitoring. (ESO)

Despite their name, super-Earths—rocky exoplanets with a mass up to 10 times our own planet’s—may be uninhabitable, and are more diverse than realized.

Using calculations to study the thermal evolution of super-Earths, a team of researchers is comparing their composition and conditions with those of Earth.

“We especially want to know if rocky super-Earths have thick atmospheres, volcanic activity, magnetic fields or plate tectonics,” said researcher Vlada Stamenkovic at the Massachusetts Institute of Technology in a press release.

“Some of these features are crucial for determining if a planet might be capable of supporting surface life.”

Plate tectonics and volcanoes on Earth recycle nutrients and regulate the climate. Also, Earth’s liquid metallic core has a dynamo action that generates a magnetic field and may prevent our atmosphere from being removed by cosmic particles.

“Current understanding is that the terrestrial planets in our solar system formed rapidly—in about the first 50 million years,” Stamenkovic said. “The time scale of core formation depends strongly on viscosity.”

Stamenkovic’s team found that a planet’s internal pressure strongly affects the melting temperature and viscosity of its mantle rock. Therefore super-Earths can have much greater internal pressures and viscosities than Earth, and may not even be differentiated into a rocky mantle and metallic core.

“The high melting temperatures and the large viscosities that we’ve calculated for super-Earths suggest either a slow core formation or no core formation at all,” Stamenkovic said. “This raises doubts about whether super-Earths could generate magnetic fields.”

Plate tectonics also become less likely with increased mass, although the presence of water can mitigate this.

“We will only be able to fully answer questions by gathering more data from high-pressure experiments and from spectroscopic observations of super-Earth atmospheres orbiting close-by bright stars,” Stamenkovic concluded.

Stamenkovic will present the research at the European Planetary Science Congress in Spain on Sept. 26.

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