This paper investigates the conventional habitable zone (HZ) concept, where a CO2-H2O greenhouse effect maintains surface liquid water, stabilized by the water-mediated carbonate-silicate weathering cycle. The authors demonstrate that this cycle should produce a log-linear relationship between atmospheric CO2 partial pressure (pCO2) and incident stellar flux on Earth-like planets within the HZ. However, variations in geophysical and physicochemical parameters introduce scatter. Using a coupled climate and weathering model, they quantify this scatter and predict a two-dimensional relationship between incident flux and pCO2. They find that at least 83 Earth-like exoplanet observations are needed to confidently detect this relationship and test the HZ hypothesis.

Owen R. Lehmer, David C. Catling, Joshua Krissansen-Totton