So far, researchers have found no evidence of global tectonic activity on planets outside our solar system. Under the guidance of University of Bern and the National Center for Competence in Research NCCR PlanetS, scientists have already found that the material inside the planet LHS 3844b flows from one hemisphere to another and may be responsible for multiple 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, which carries material from the interior of the planet to the surface and atmosphere and then transports it back under the earth’s crust. In this way, tectonics has a vital influence on the conditions that ultimately make the Earth habitable.
So far, researchers have found no evidence of global tectonic activity on planets outside our solar system. A team of researchers led by Tobias Meyer from the Center for Space and Habitat (CSH) at the University of Bern and with the participation of ETH Zurich, University of Oxford and the National Center for Competence in Research NCCR PlanetS has already found evidence for patterns of flux inside a planet 45 light-years from Earth: LHS 3844b. The results were published in Astrophysical Journal Letters.
Exceptional contrast and lack of atmosphere
“Observing signs of tectonic activity is very difficult because they are usually hidden under the atmosphere,” Meyer explains. Recent results, however, suggest that the LHS 3844b may not have an atmosphere. Slightly larger than Earth and probably just as rocky, it orbits its star so close that one side of the planet is in constant daylight and the other in constant night, just as the same side of the moon is always facing Earth. Without an atmosphere to protect it from intense radiation, the surface heats up hot: it can reach 800 ° C during the day. The night side, on the other hand, freezes. Temperatures there could drop below minus 250 ° C. “We thought that this strong temperature contrast could affect the material flow inside the planet,” Meyer recalled.
To test their theory, the team conducted computer simulations with different material strengths and internal heating sources, such as heat from the planet’s core and the decay of radioactive elements. The simulations involve the high surface temperature contrast imposed by the host star.
Flow inside the planet from one hemisphere to another
“Most simulations have shown that there is only upward flow on one side of the planet and downstream on the other. Therefore, the material spilled from one hemisphere to the other, “Meyer said. Surprisingly, the direction was not always the same. “Based on what we’re used to from Earth, you’d expect the material to be lighter on a hot day and therefore flow up and back,” explains co-author Dan Bauer of the University of Bern and NCCR PlanetS. However, some of the team simulations also showed the opposite direction of the flow. “This initially counter-intuitive result is due to the change in viscosity with temperature: the cold material is harder and therefore does not want to bend, break or enter the interior. However, the warm material is less viscous – so even hard rock becomes more mobile when heated – and can easily flow to the interior of the planet, “said Bower. In any case, these results show how the planetary surface and the interior can exchange material under conditions very different from those on Earth.
Such a material flow can have strange consequences. “From whichever side of the planet the material flows upwards, a large amount of volcanism can be expected from that side,” Bauer said. He continued, “Such deep uplifts on Earth drive volcanic activity in Hawaii and Iceland.” Therefore, one can imagine a hemisphere with countless volcanoes – a volcanic hemisphere, so to speak – and one with almost none.
“Our simulations show how such models can manifest themselves, but more detailed observations will be needed to verify. For example, with a map with a higher surface temperature resolution, which may lead to enhanced gas evolution from volcanism or the detection of volcanic gases. This is something we hope future research will help us understand, “Meyer said.
Reference: “Hemispherical tectonics of LHS 3844b” by Tobias G. Meier, Dan J. Bower, Tim Lichtenberg, Paul J. Tackley and Brice-Olivier Demory, 24 February 2021, 2021, Astrophysical Journal Letters.
DOI: 10.3847 / 2041-8213 / abe400