Ocean, atmosphere, and cloud quantity on the surface conditions of tidally-locked habitable zone planets

The study of tidally-locked planets has become an active field of research in recent years due to their interesting properties and abundance in the universe. As one hemisphere of these planets is always facing a star and the other is covered in perpetual darkness, habitable conditions on such extreme worlds were generally considered impossible. However, recent studies have shown that under specific planetary atmospheric and oceanic conditions, temperatures could stay mild enough for the planet to be habitable. In this paper, we created an energy balance model to determine the atmospheric and surface temperatures of tidally-locked worlds as a function of several planetary factors. We hypothesized that these factors—atmospheric and oceanic heat circulation and clouds—are crucial for habitable conditions to exist on these planets. We then assessed what specific set of values of these factors would make habitable conditions possible. We found that global heat transportation cycles act as a major determining factor on the planetary climate and, therefore, habitability. Apart from being in the habitable zone, Earth-like oceans and atmospheric coverage could also be essential for the habitability of tidally-locked planets, which establishes viable criteria in future searches for extraterrestrial life and livable worlds.