Modeling the Habilability of Terrestrial Worlds With High obliquity and Eccentric Orbits

Habitability of Earth-like planets with high obliquity and eccentric orbits: results from a general circulation model

Authors:

Linsenmeier et al

Abstract:

We explore the implications of seasonal variability for the habitability of Earth-like planets as determined by the two parameters polar obliquity and orbital eccentricity. Commonly, the outer boundary of the habitable zone (HZ) is set by a completely frozen planet, or snowball state. Using a general circulation model coupled to a thermodynamic sea-ice model, our results show that seasonal variability can extend this outer limit of the HZ from 1.03 AU (no seasonal variability) to a maximum of 1.69 AU. Also the multistability property of planets close to the outer edge of the HZ is influenced by seasonal variability. Cold states extend far into the HZ for non-oblique planets. On highly oblique planets, cold states can also allow for habitable regions, which highlights the sufficient but not necessary condition of a warm climate state for habitability. While the effect of obliquity on the extent of the HZ is comparatively small on circular orbits, it becomes highly relevant on eccentric orbits. Our experiments show, however, that the extending effect on the HZ is very sensitive to the definition of habitability, as seasonal variability primarily leads to regions that are habitable only some days per year. Sensitivity experiments exploring the role of azimuthal obliquity, surface heat capacity, and maximal sea-ice thickness show the robustness of our results. On circular orbits, our results are in good agreement with previous studies that use a one-dimensional energy balance model. Yet on eccentric orbits large differences hint to limitations of these simpler models and underline the importance of using a hierarchy of models in order to provide reliable estimations of the effects of seasonal variability on climate.