With thousands of planet candidates detected by the Kepler mission, the question of their habitability is naturally raised. The identified planets are very diverse in their masses, sizes, orbital parameters, compositions, etc; the physical processes and range of parameters underlying the habitability question are vast. Here, we explore the constraints on habitability brought by the orbital configuration of a planet. We consider two cases characterized by large solar radiation contrasts potentially limiting habitability: 1) a high obliquity planet where the seasonal cycle is extreme as the poles alternate between months of continuous day-light and months of continuous night and 2) a tidally-locked planet where one hemisphere permanently faces the star while the other hemisphere is in complete darkness.
A General Circulation Model of the coupled atmosphere-ocean-sea ice system is used to determine the climates of these planets. The dynamics of the circulation will be discussed. A key finding of our experiments is that in both cases, a habitable planet is possible with moderate temperatures in the range 280–300 K provided a deep enough ocean exists. This is largely due to the ability of oceans to transport and store large amounts of heat to mitigate the extreme solar forcing.