EVOLUTIONARY CLIMATE TRACKS OF EARTH-LIKE PLANETS

Abstract

Recent studies have revealed that, in addition to insolation, the CO2 degassing rate is an important limiting factor on the resulting climate of Earth-like The CO2 degassing rate should change with time owing to the thermal evolution of planetary interiors. Here we use a mantle degassing model coupled with a parameterized convection model to estimate the climatic evolution of Earth-like planets with different masses and distances from their central stars. The CO2 degassing rate decreases monotonically with time owing to the decreasing mantle temperature. The CO2 degassing rate for large planets is higher than that for small planets because the interiors of large planets are hotter than those of small However, the effects arising from the difference in CO2 degassing rate could be compensated by the difference in the silicate weathering rate derived from the difference in the surface area among planets with different size and with a similar land/sea ratio as the Earth. These results indicate that most of the Earth-like planets in the outer regions of the habitable zones (HZs) of old planetary systems are in the climate mode (i.e., oscillating between and warm states), irrespective of planetary mass. Because the state lasts much longer than the warm climate state, Earth-like planets in HZs around old stars would statistically be observed as snowball planets.