The Effect of Planetary Illumination on Climate Modelling of Earthlike Exomoons

TL;DR

This study models the climate of Earthlike exomoons considering planetary illumination, eclipses, and tidal heating, revealing how these factors influence the habitable zone boundaries around exoplanets.

Contribution

It introduces the first climate models of exomoons that incorporate all key energy sources and sinks, expanding previous models to include planetary illumination effects.

Findings

Planetary illumination extends the exomoon habitable zone slightly outward.

Eclipses can create an inner habitable edge on exomoons.

The carbonate-silicate cycle can push the outer habitable edge further out.

Abstract

From analytical studies of tidal heating, eclipses and planetary illumination, it is clear that the exomoon habitable zone (EHZ) - the set of moon and host planet orbits that permit liquid water on an Earthlike moon's surface - is a manifold of higher dimension than the planetary HZ. This paper outlines the first attempt to produce climate models of exomoons which possess all the above sources and sinks of energy. We expand on our previous 1D latitudinal energy balance models (LEBMs), which follow the evolution of the temperature on an Earthlike moon orbiting a Jupiterlike planet, by adding planetary illumination. We investigate the EHZ in four dimensions, running two separate suites of simulations. The first investigates the EHZ by varying the planet's orbit, keeping the moon's orbit fixed, to compare the EHZ with planetary habitable zones. In general, planetary illumination pushes EHZs slightly further away from the star. Secondly, we fix the planet's orbit and vary the moon's orbit, to investigate the circumplanetary inner habitable edge. We demonstrate that an outer edge can exist due to eclipses (rather than merely orbital stability), but this edge may be pushed outwards when the effect of the carbonate-silicate cycle is taken into account.