Proxima b, TRAPPIST 1e, and LHS 1140b: Increased Ice Coverages by Sea Ice Dynamics

The three nearby tidally locked exoplanets--Proxima b, TRAPPIST 1e, and LHS 1140b will be the prime targets for future atmosphere and climate observations for finding habitable systems. Previous climate studies suggest that these planets would be ice-free in the sub-stellar region and ice-covered in other regions if assuming they have surface oceans. Through comparing 3D climate simulations with versus without sea ice dynamics, here we show that wind-driven sea ice flows toward the sub-stellar region strongly shrink the ice-free coverages and even drive the planets into globally ice-covered snowball states. For example, previous studies shown that TRAPPIST 1e will be ice-free in the substellar region regardless of its atmosphere. After sea ice flows are included, we find that a CO2 concentration of >1,000 ppmv is required to avoid it falling into a snowball glaciation. Our results suggest that ice dynamics are critical for predicting the possible climates and meanwhile observational characteristics of terrestrial planets in the habitable zone around low-mass stars.