Geodynamics of super-Earth GJ 486b

TL;DR

This study explores how the interior dynamics and tectonic patterns of super-Earth GJ 486b are affected by surface temperature contrasts and lithosphere strength, highlighting the potential for hemispheric tectonics driven by interior properties.

Contribution

It provides new insights into the influence of atmospheric and surface temperature regimes on the geodynamics of tidally locked super-Earths, emphasizing the role of lithosphere strength in tectonic patterns.

Findings

Hemispheric tectonics result from strong lithosphere, not temperature contrast.

Anchored hemispheric tectonics are favored by high temperature contrasts.

Surface temperature contrast influences tectonic regime and convection patterns.

Abstract

Many super-Earths are on very short orbits around their host star and, therefore, more likely to be tidally locked. Because this locking can lead to a strong contrast between the dayside and nightside surface temperatures, these super-Earths could exhibit mantle convection patterns and tectonics that could differ significantly from those observed in the present-day solar system. The presence of an atmosphere, however, would allow transport of heat from the dayside towards the nightside and thereby reduce the surface temperature contrast between the two hemispheres. On rocky planets, atmospheric and geodynamic regimes are closely linked, which directly connects the question of atmospheric thickness to the potential interior dynamics of the planet. Here, we study the interior dynamics of super-Earth GJ 486b ($R=1.34$ $R_{\oplus}$, $M=3.0$ $M_{\oplus}$, T$_\mathrm{eq}\approx700$ K), which is one of the most suitable M-dwarf super-Earth candidates for retaining an atmosphere produced by degassing from the mantle and magma ocean. We investigate how the geodynamic regime of GJ 486b is influenced by different surface temperature contrasts by varying possible atmospheric circulation regimes. We also investigate how the strength of the lithosphere affects the convection pattern. We find that hemispheric tectonics, the surface expression of degree-1 convection with downwellings forming on one hemisphere and upwelling material rising on the opposite hemisphere, is a consequence of the strong lithosphere rather than surface temperature contrast. Anchored hemispheric tectonics, where downwellings und upwellings have a preferred (day/night) hemisphere, is favoured for strong temperature contrasts between the dayside and nightside and higher surface temperatures.