Liquid water on cold exo-Earths via basal melting of ice sheets

Liquid water is a critical component of habitability. However, the production and stability of surficial liquid water can be challenging on planets outside the Habitable Zone and devoid of adequate greenhouse warming. On such cold, icy exo-Earths, basal melting of regional/global ice sheets by geothermal heat provides an alternative means of forming liquid water. Here, we model the thermophysical evolution of ice sheets to ascertain the geophysical conditions that allow liquid water to be produced and maintained at temperatures above the pressure-controlled freezing point of water ice on exo-Earths. We show that even with a modest, Moon-like geothermal heat flow, subglacial oceans of liquid water can form at the base of and within the ice sheets on exo-Earths. Furthermore, subglacial oceans may persist on exo-Earths for a prolonged period due to the billion-year half-lives of heat-producing elements responsible for geothermal heat. These subglacial oceans, often in contact with the planet's crust and shielded from the high energy radiation of their parent star by thick ice layers, may provide habitable conditions for an extended period. Liquid water is key for life as we know it. Here, the authors show even with a modest geothermal heat flow, subglacial oceans of liquid water can form at the base of and within the ice sheets on exo-Earths, which may provide habitable conditions for an extended period.

Automated summary

The presence of liquid water is crucial for habitability, and new research suggests that on icy exo-Earths outside the habitable zone, subglacial oceans of liquid water can form at the base and within the ice sheets due to geothermal heat flow. These subglacial oceans, shielded by thick ice layers, may provide habitable conditions for an extended period.