| Summary: | A planet’s surface conditions can significantly impact its climate and habitability. In this work, we use the 3D general circulation model ExoPlaSim to systematically vary dayside land cover on a tidally locked rocky planet under two extreme and opposite continent configurations: either all of the land or all of the ocean is centred at the substellar point. We identify water vapour and sea ice as competing drivers of climate, and we identify land-dependent regimes under which one or the other dominates. We find that land fraction and distribution can change the globally averaged surface temperature by up to 15K, and water vapour by up to an order of magnitude. The most discrepant models have partial dayside land cover with opposite continent configuration. Since these planets’ surfaces will not be directly observable using transit spectroscopy, these climate differences likely represent a fundamental uncertainty in the climates of tidally locked planets, even if their atmospheric composition is well-known.
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