This artist’s illustration represents the possible interior dynamics  of the super-Earth exoplanet LHS 3844b. The planet’s interior  properties and the strong stellar irradiation might lead to a  hemispheric tectonic regime. © Universität Bern / University of Bern, Illustration: Thibaut Roger

Until now, researchers have found no evideDismissnce of global tectonic activity on planets outside  our solar system. Under the leadership of the University of Bern and the National Center of  Competence in Research NCCR PlanetS, scientists have now found that the material inside  planet LHS 3844b flows from one hemisphere to the other and could be responsible for  numerous volcanic eruptions on one side of the planet.  

On Earth, plate tectonics is not only responsible for the rise of mountains and earthquakes. It is also  an essential part of the cycle that brings material from the planet’s interior to the surface and the  atmosphere, and then transports it back beneath the Earth’s crust. Tectonics thus has a vital influence  on the conditions that ultimately make Earth habitable. 

Until now, researchers have found no evidence of global tectonic activity on planets outside our solar  system. A team of researchers led by Tobias Meier from the Center for Space and Habitability (CSH)  at the University of Bern and with the participation of ETH Zurich, the University of Oxford and the  National Center of Competence in Research NCCR PlanetS has now found evidence of the flow  patterns inside a planet, located 45 light-years from Earth: LHS 3844b. Their results were published in  The Astrophysical Journal Letters. 

An extreme contrast and no atmosphere 

“Observing signs of tectonic activity is very difficult, because they are usually hidden beneath an  atmosphere”, Meier explains. However, recent results suggested that LHS 3844b probably does not  have an atmosphere. Slightly larger than Earth and likely similarly rocky, it orbits around its star so  closely that one side of the planet is in constant daylight and the other in permanent night – just like  the same side of the Moon always faces the Earth. With no atmosphere shielding it from the intense  radiation, the surface gets blisteringly hot: it can reach up to 800°C on the dayside. The night side, on  the other hand, is freezing. Temperatures there might fall below minus 250°C. “We thought that this  severe temperature contrast might affect material flow in the planet’s interior”, Meier recalls. To test their theory, the team ran computer simulations with different strengths of material and internal  heating sources, such as heat from the planet’s core and the decay of radioactive elements. The  simulations included the large temperature contrast on the surface imposed by the host star. 

Flow inside the planet from one hemisphere to the other 

“Most simulations showed that there was only upwards flow on one side of the planet and downwards flow on the other. Material therefore flowed from one hemisphere to the other”, Meier reports. 

Surprisingly, the direction was not always the same. “Based on what we are used to from Earth, you  would expect the material on the hot dayside to be lighter and therefore flow upwards and vice versa”,  co-author Dan Bower at the University of Bern and the NCCR PlanetS explains. Yet, some of the  teams’ simulations also showed the opposite flow direction. “This initially counter-intuitive result is due  to the change in viscosity with temperature: cold material is stiffer and therefore doesn’t want to bend,  break or subduct into the interior. Warm material, however, is less viscous – so even solid rock  becomes more mobile when heated – and can readily flow towards the planet’s interior”, Bower  elaborates. Either way, these results show how a planetary surface and interior can exchange material  under conditions very different from those on Earth.  

A volcanic hemisphere 

Such material flow could have bizarre consequences. “On whichever side of the planet the material  flows upwards, one would expect a large amount of volcanism on that particular side”, Bower points  out. He continues “similar deep upwelling flows on Earth drive volcanic activity at Hawaii and Iceland”.  One could therefore imagine a hemisphere with countless volcanoes – a volcanic hemisphere so to  speak – and one with almost none. 

“Our simulations show how such patterns could manifest, but it would require more detailed  observations to verify. For example, with a higher-resolution map of surface temperature that could  point to enhanced outgassing from volcanism, or detection of volcanic gases. This is something we  hope future research will help us to understand”, Meier concludes. 

Publication details: 

  1. G. Meier et al.: Hemispheric Tectonics on LHS 3844b, The Astrophysical Journal Letters DOI: https://doi.org/10.3847/2041-8213/abe400