Determine Inner Edge of Habitable Zone for Eccentric Exoplanets

A planet’s climate can be strongly affected by its orbital eccentricity due to variations in incident stellar flux. Eccentric exoplanets within or near the habitable zone can possibly harbor life if the temperature changes are not too drastic. We build a time-dependent energy balance model to resolve the temperature evolution on eccentric planets located near the habitable zone. We consider energy storage by the atmosphere, ocean, and land. We find that the ocean plays an essential role in maintaining habitable surface conditions (liquid water possible) by suppressing the surface temperature at periastron. Surprisingly, the ocean only needs to be about 10-m deep to significantly reduce the surface temperature at periastron. We also find that the inner edge of the habitable zone does not depend strongly on eccentricity for eccentricities less than 0.5. Above this threshold, higher eccentricity leads to much warmer surface temperatures at periastron, pushing the inner edge of the habitable zone away from the star. Our work suggests that estimates of the inner edge of the habitable zone made with zero eccentricity do not need to be significantly modified for most observed terrestrial exoplanets, which have eccentricities less than 0.5.