10:00 AM - 10:15 AM
[PPS21-31] The duration of habitable condition for large and small Earth-like planets
Keywords:exoplanet, habitable zone
In this study, we apply a parameterized convection model to the thermal evolution of the Earth-like planet with different masses and with plate-tectonics in order to estimate the evolution of average mantle temperature, seafloor spreading rate, melt generation depth, melt production rate, and the CO2 degassing rate for the planets. The results are compared with the climate mode diagram for the Earth-like planets proposed by Kadoya & Tajika (2014), and also, the evolutions of the climate of the Earth-like planet are discussed.
The average mantle temperature monotonically decreases with time when an initial average mantle temperature is higher than 3000 K. As expected, the average mantle temperatures of large planets cool more slowly than that of small planets do. However, the difference between the mantle temperatures of the planets is smaller than 100 K, which is consistent with the recent work (e.g., Schaefer & Sasselov, 2015). The seafloor spreading rate is larger on large planets than on small planets because the heat flow is higher on large planets than on small planets. On the other hand, the melt generation depth of large planets is smaller than that of small planets owing to the difference in the surface gravity. The net result of the melt generation rate is larger on large planets than on small planets although the difference is smaller than those of the seafloor spreading rate and the melt generation depth. In addition, because large planets have a larger surface area than small planets, the CO2 uptake rate via silicate weathering on large planet is larger than that on small planets when the temperature distribution is the same. As a result, the climate evolutions of large and small planets are almost the same as long as the areal ratio of continents and oceans is the same.