Exoplanet Plate Tectonics May Have Required an Early Start

An artist’s illustration of the potentially habitable exoplanet Kepler-1649c. Image credit: NASA/Ames Research Center/Daniel Rutter

Getting an early start may have helped rocky exoplanets in the race for habitability, according to researchers at Macquarie University in Sydney, Australia. Plate tectonics is considered an important factor in the habitability of terrestrial planets. This process provides long-term regulation of a planet’s heat and chemical budgets and helps maintain a magnetic field that protects the surface from harmful solar radiation. Without plate tectonics, an exoplanet otherwise similar to Earth may be more likely to end up uninhabitable like Venus.

The ability of a planet to initiate plate tectonics is dependent on the balance of chemical components with which it forms. Especially important are rock-forming elements like iron and silicon, and heat-producing elements such as potassium, uranium, and thorium. The initial distribution of elements is dependent on the composition of the solar nebula in which the planet forms, which in turn evolves over the age of the Milky Way as stars produce these geophysically critical elements through supernovae or the elements radioactively decay over time.

Craig O’Neill of the University of Macquarie and colleagues modeled the initiation of plate tectonics in terrestrial planets, varying the elemental composition to match the trends expected by galactic chemical evolution models. They found that planets that formed around stars early in galactic history were likely to have more silicon than iron, resulting in small cores, large mantles, and enhanced tectonic activity at the surface. Planets that formed later were more likely to have large cores and less propensity for plate tectonics. The researchers conclude that planets that formed early in the Milky Way’s history were more likely to have developed plate tectonics and be more favorable to life. As the galaxy ages, planets like the Earth will become more and more rare. Developing and sustaining life requires a planet to have many factors in its favor, and getting an early start may be part of that process. READ MORE