The Snowball Bifurcation on Exoplanets

Abstract: The Snowball Earth episodes may have affected the development of life on Earth through increasing atmospheric oxygen and spurring evolution. Considering the habitability and increase in complexity of life on other planets therefore requires thought about Snowball climate states. Using an energy balance model and global climate model, I will show that it is unlikely a tidally locked planet could experience a Snowball Earth bifurcation. Instead the planet would smoothly transition to global ice coverage. This is due to the difference in the shape of the insolation, which increases strongly toward the substellar point on a tidally locked planet. I will then change focus slightly and explain how climate oscillations between a warm state and a Snowball state can occur on a planet within the habitable zone that has a small CO2 outgassing rate. I will develop analytical relations to understand these cycles and outline scalings in variables such as the cycle period as a function of important climatic and weathering parameters. Work of this type should help us understand the context of planetary habitability and focus on appropriate targets as we seek to find the first inhabited exoplanet. Close abstractClose abstract