Interior Structures and Potential Habitability of the Super-Earth Exoplanets LHS 1140 b, K2-18 b, TOI-1452 b and TOI-1468 c

Mangesh Daspute

Ariel University

The super-Earth exoplanets LHS 1140 b, K2-18 b, TOI-1452 b, and TOI-1468 c are

orbiting M-dwarf stars in the habitable zone. Their relative proximity, within 40
parsecs, makes them prime candidates for follow-up observations and
atmospheric and habitability studies. In a recent work we assessed their
habitability, considering their internal structure, tidal heating, atmospheric
heating, and global transport factors. We model the interior structure of the
planets by applying Bayesian inference to an exoplanet’s interior model. A
constant quality factor model is used to calculate the range of tidal heating, and a
one-dimensional analytical model of tidally-locked planets is used to assess their
habitability. Assuming no or only thin atmospheres, K2-18 b and TOI-1468 c are
likely to be water worlds. However, TOI-1452 b and LHS 1140 b can have rocky
surfaces. Considering the atmosphere as a fourth layer reduces the median size of
the water ice layer in all four exoplanets. We find that tidal heating is not enough
to raise the global mean surface temperature, but atmospheric heating through
the greenhouse effect can effectively do so. If the considered planets have
retained thick atmospheres, K2-18 b, TOI-1468 c, and TOI-1452 b may, for
significant atmospheric heating and heat transport factors, be too hot to sustain
life. However, the lower instellation of LHS 1140 b and its significant probability of
having a rocky surface give more space for habitable conditions on the planet,
even in the case of a highly transporting atmosphere.