  The tectonic regime of rocky planets fundamentally influences their long-term
evolution and cycling of volatiles between interior and atmosphere. Earth is
the only known planet with active plate tectonics, but observations of
exoplanets may deliver insights into the diversity of tectonic regimes beyond
the solar system. Observations of the thermal phase curve of super-Earth LHS
3844b reveal a solid surface and lack of a substantial atmosphere, with a
temperature contrast between the substellar and antistellar point of around
1000 K. Here, we use these constraints on the planet's surface to constrain the
interior dynamics and tectonic regimes of LHS 3844b using numerical models of
interior flow. We investigate the style of interior convection by assessing how
upwellings and downwellings are organized and how tectonic regimes manifest. We
discover three viable convective regimes with a mobile surface: (1) spatially
uniform distribution of upwellings and downwellings, (2) prominent downwelling
on the dayside and upwellings on the nightside, and (3) prominent downwelling
on the nightside and upwellings on the dayside. Hemispheric tectonics is
observed for regimes (2) and (3) as a direct consequence of the day-to-night
temperature contrast. Such a tectonic mode is absent in the present-day solar
system and has never been inferred from astrophysical observations of
exoplanets. Our models offer distinct predictions for volcanism and outgassing
linked to the tectonic regime, which may explain secondary features in phase
curves and allow future observations to constrain the diversity of super-Earth
interiors.
