Habitable Snowballs: Temperate Land Conditions, Liquid Water, and Implications for CO$_2$ Weathering

TL;DR

This paper demonstrates that planets in snowball states can have large unfrozen land areas with warm temperatures, enabling CO2 weathering and challenging traditional views of snowball inhospitable conditions.

Contribution

It reveals that snowball planets can support temperate land regions, affecting their climate stability and habitability assessments.

Findings

Large unfrozen land areas can exist in snowball states.

Temperate land regions enable CO2 weathering during snowball periods.

Snowball planets may sustain habitable conditions on land.

Abstract

Habitable planets are commonly imagined to be temperate planets like Earth, with areas of open ocean and warm land. In contrast, planets in snowball states, where oceans are entirely ice-covered, are believed to be inhospitable. However, we show using a general circulation model that terrestrial planets in the inner habitable zone are able to support large unfrozen areas of land while in a snowball state. Due to their lower albedo, these unfrozen regions reach summer temperatures in excess of 10 $^\circ$Celsius. Such conditions permit CO$_2$ weathering, suggesting that continental weathering can provide a mechanism for trapping planets in stable snowball states. The presence of land areas with warm temperatures and liquid surface water motivates a more-nuanced understanding of habitability during these snowball events.