Nightside of Hot Super-Earth LHS 3844b is Tectonically Active: Study | Astronomy

LHS 3844b’s hemispheric tectonics is the direct consequence of a significant temperature contrast between its day- and nightside and is absent in the present-day Solar System.

This illustration shows the possible interior dynamics of the hot super-Earth LHS 3844b. Image credit: Thibaut Roger / University of Bern.

Discovered in 2018 by NASA’s TESS mission, LHS 3844b has a radius 1.3 times that of Earth and an orbital period of 11 hours.

It orbits LHS 3844, an M dwarf (red dwarf) star located about 49 light-years away in the constellation of Indus.

LHS 3844b is ‘tidally locked’ with one side of the planet permanently facing the star.

It star-facing side, or dayside, is about 770 degrees Celsius (1,410 degrees Fahrenheit).

The nightside, on the other hand, is much colder, with temperatures below minus 250 degrees Celsius (minus 418 degrees Fahrenheit).

“We thought that this severe temperature contrast might affect material flow in the planet’s interior,” said lead author Dr. Tobias Meier, an astronomer in the Center for Space and Habitability at the University of Bern.

To test their theory, Dr. Meier and colleagues 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.

“Most simulations showed that there was only upwards flow on one side of the planet and downwards flow on the other,” Dr. Meier said.

“Material therefore flowed from one hemisphere to the other. 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,” said co-author Dr. Dan Bower, also from the Center for Space and Habitability at the University of Bern.

“Yet, some of the 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.”

“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,” he added.

“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,” Dr. Meier said.

“This is something we hope future research will help us to understand.”

A paper on the findings was published in the Astrophysical Journal Letters.

_____

Tobias G. Meier et al. 2021. Hemispheric Tectonics on LHS 3844b. ApJL 908, L48; doi: 10.3847/2041-8213/abe400