Habitability of Earth-like Stagnant Lid Planets: Climate Evolution and Recovery from Snowball States

Coupled models of mantle thermal evolution, volcanism, outgassing, weathering, and climate evolution for Earth-like (in terms of size and composition) stagnant lid planets are used to assess their prospects for habitability. The results indicate that planetary CO2 budgets ranging from approximate to 3 orders of magnitude lower than Earth's to approximate to 1 order of magnitude larger, along with radiogenic heating budgets as large or larger than Earth's, allow for habitable climates lasting 1-5 Gyr. The ability of stagnant lid planets to recover from potential snowball states is also explored; recovery is found to depend on whether atmosphere-ocean chemical exchange is possible. For a "hard" snowball with no exchange, recovery is unlikely, as most CO2 outgassing takes place via metamorphic decarbonation of the crust, which occurs below the ice layer. However, for a "soft" snowball where there is exchange between atmosphere and ocean, planets can readily recover. For both hard and soft snowball states, there is a minimum CO2 budget needed for recovery; below this limit, any snowball state would be permanent. Thus, there is the possibility for hysteresis in stagnant lid planet climate evolution, where planets with low CO2 budgets that start off in a snowball climate will be permanently stuck in this state, while otherwise identical planets that start with a temperate climate will be capable of maintaining this climate for 1 Gyr or more. Finally, the model results have important implications for future exoplanet missions, as they can guide observations to planets most likely to possess habitable climates.