The Effect of Continental Location on Climate of Synchronously Rotating Exoplanets

Abstract:

Abundant potentially habitable synchronously exoplanets have been observed around M dwarfs. Lots of attention has thus been paid to the climate and habitability of such planets. Many studies assumed that these exoplanets were covered by oceans, i.e., aquaplanets, only a few of them investigated the influence of a continent residing under the substellar point. It has been shown that climate changes only when the size of the continent is large; it cools due to changes of surface albedo, hydrological cycle and cloud. Here we show that the climate of a synchronously exoplanet is highly sensitive to the continental location even if the size is small. The climate can either cool or warm, and the global mean surface temperature can change by over 26 °C just by varying the location of an idealized circular continent on the dayside. We found that the albedo effect of the continent plays a negligible role in this climate sensitivity, while the modulation of the ocean current by the continent is much more important. The warmest climate occurs when the continent is located on the northeast or southeast of substellar point, when the equatorial westerly will be strengthened. The coldest climate occurs when the continent blocks the equatorial westerly from the west of substellar point. The threshold stellar-planet distance at which a snowball state occurs, i.e., the outer edge of the habitable zone, can change by ~10% depending on the location of continent. These results suggest that the continental configuration may significantly impact the habitability of synchronously planets around M dwarf.