Astronomers may have found the first evidence for tectonic activity on an exoplanet

On Earth, the heat from the radioactive decay of elements in the Earth’s crust drives convection currents, pushing and dragging large plates of Earth’s crust around. When the plates collide, mountains form, and parts of the Earth’s crust are recycled into the mantle. When the plates are pushed apart, the molten mantle rises to fill the gap. Plate tectonics are an essential part of the circle that carry material from the inside of the planet to the surface and atmosphere, and then transport it back under the Earth’s crust. Tectonics therefore have an important influence on energy transfer and an issue that ultimately makes the Earth a place to live.

To date, 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 Space (CSH) at the University of Bern and with the participation of ETH Zurich, University of Oxford, and the National Capability Center for Research NCCR PlanetS has now found evidence of the flow patterns within a planet, located 45 light-years from Earth: LHS 3844b. Their findings were published in Letters of the Astrophysical Journal.

LHS 3844 b is an exoplanet orbiting the red star LHS 3844, which was detected using the Transiting Exoplanet Survey Satellite. It moves around its parent star once every 11 hours, and its radius is 1.32 times greater than that on Earth. It has a low albedo, indicating that its surface could resemble the surface of the moon or mercury.

“Monitoring for signs of tectonic activity is very difficult, as they are usually hidden under an atmosphere,” explains Meier. However, recent results have suggested that LHS 3844b may not have an atmosphere. Slightly larger than Earth and seemingly rocky, it moves around its star so closely that one side of the planet is suddenly locked towards the sun. One hemisphere of the planet is in stable daylight and the other in permanent night light. Without any atmosphere protecting it from the intense radiation, the surface becomes very hot: it can reach up to 800 ° C on the daytime side. Common rocks, such as granite and basalt, melt at temperatures of 900 to 1,200 degrees Celsius. The night side, on the other hand, is freezing. Temperatures can drop below less than 250 ° C. “We thought that this adverse temperature difference could affect the flow of materials in the interior of the planet”, Meier recalls.

Cool rocks are brittle and prone to breakage, becoming more like liquid as they heat up. The team ran computer simulations with varying strengths of materials and internal heating sources, such as heat from the planet’s core and the decay of radioactive elements. The symbols included the large surface temperature difference placed by the host star.

“Most symbols showed that there was only flow up on one side of the planet and flow down on the other side. So material was flowing from one hemisphere to the other,” Meier reports. Surprisingly, the instructions were not always the same. “Based on what we are used to from Earth, you would expect the material on the hot day to be lighter and therefore flow up and vice versa”, co-author Dan Bower of the University of Bern and the NCCR PlanetS explaining. However, some team symbols showed the opposite side of a stream. “This inconvenient result is initially due to the change in viscosity with temperature: cold material is harder and therefore does not want to bend, break or penetrate into the becomes more mobile when heated – and can easily flow into the interior of the planet “, Bower edits. Either way, these results show how the surface of a planet and its interior can exchange material under very different conditions from those on Earth.