Models of thermal evolution, crustal production, and CO$_2$ cycling are usedto constrain the prospects for habitability of rocky planets, with Earth-likesize and composition, in the stagnant lid regime. Specifically, we determinethe conditions under which such planets can maintain rates of CO$_2$ degassinglarge enough to prevent global surface glaciation, but small enough so as notto exceed the upper limit on weathering rates provided by the supply of freshrock, a situation which would lead to runaway atmospheric CO$_2$ accumulationand an inhospitably hot climate. The models show that stagnant lid planets withinitial radiogenic heating rates of 100-250 TW, and with total CO$_2$ budgetsranging from $\sim 10^{-2} -1$ times Earth's estimated CO$_2$ budget, canmaintain volcanic outgassing rates suitable for habitability for $\approx 1-5$Gyrs; larger CO$_2$ budgets result in uninhabitably hot climates, while smallerbudgets result in global glaciation. High radiogenic heat production ratesfavor habitability by sustaining volcanism and CO$_2$ outgassing longer. Thus,the results suggest that plate tectonics may not be required for establishing along-term carbon cycle and maintaining a stable, habitable climate. The modelis necessarily highly simplified, as the uncertainties with exoplanet thermalevolution and outgassing are large. Nevertheless, the results provide somefirst order guidance for future exoplanet missions, by predicting the age atwhich habitability becomes unlikely for a stagnant lid planet as a function ofinitial radiogenic heat budget. This prediction is powerful because both planetheat budget and age can potentially be constrained from stellar observations.
展开▼
