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First proof of tectonic activity on an exoplanet?

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A team of researchers assumes the existence of hemispherical tectonic activity on the exoplanet LHS 3844b. It would be the direct consequence of a significant temperature contrast between its “day side” and its “night side”. Their work is published in Letters from the astrophysical journal.

Discovered in 2018 by NASA’s TESS satellite, LHS 3844b is an exoplanet a little larger than Earth (1.3 times its radius), evolving around a red dwarf star located about 49 light years towards the Indian, a constellation in the southern hemisphere.

LHS 3844b completes one turn of its star in just eleven o’clock. This astonishing proximity implies a “locked” orbit. In other words, the exoplanet has only one face to its star like the Moon with the Earth. In fact, its “day” side records a temperature of around 770 ° C, while its night side is much colder with temperatures below –250 ° C.

Astronomer Tobias Meier, of the University of Bern and lead author of this study, believed that this temperature contrast could affect the flow of matter inside the planet. To test his theory with his team, they performed computer simulations involving different forces of materials and internal heat sources.

Hemispherical tectonic activity

This work revealed an upward flow of matter on one side of the planet and a downward flow on the other. In other words, the matter circulated from one hemisphere to another.

These simulations also revealed something astonishing. Based on what we are used to on Earth, we might expect the material on the warm side of the day to be lighter and therefore flow upward and vice versa. Yet some of the simulations also revealed an opposite direction of flow.

This counterintuitive result is due to the change in viscosity with temperature: the cold material is more rigid and therefore does not want to bend, break or escape inside.“, Says Dr. Dan Bower, co-author of the study. “The hot material, however, is less viscous. So even solid rock becomes more mobile when heated. It can therefore easily flow into the interior of the planet“.

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

According to the researcher, such a flow of materials could have strange consequences. “Regardless of which side of the planet the material is flowing upwards, we would expect a large amount of volcanism from that side. Similar deep upwelling on Earth stimulates volcanic activity in Hawaii and Islande. So we could imagine a hemisphere punctuated by innumerable volcanoes, and almost without a volcano“, He concludes.

It should be noted that this work is only based on simulations. More detailed observations such as a map of surface temperatures indicating increased degassing of volcanism or detection of volcanic gases could confirm these results.


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