Habitable Snowballs: Generalizing the Habitable Zone

Adiv Paradise, Kristen Menou, Diana Valencia, Christopher Lee

Published 2018-03-01Version 1

Habitable planetary are commonly imagined to be temperate planets like Earth, with areas of open ocean and warm land. In contrast, planets with colder surfaces and permanent snowball states, where oceans are entirely ice-covered, are believed to be inhospitable. However, we show using a general circulation model that terrestrial habitable zone planets are able to support large unfrozen areas of land even while in a snowball state. These unfrozen regions reach summer temperatures in excess of 10 $^\circ$Celsius and develop their own hydrological cycles. Such conditions permit substantial carbon dioxide weathering, allowing these snowballs to become stable climate states, rather than transient as is commonly assumed. Glaciated planets can thus be habitable, which represents a generalization of the habitable zone concept.