Desert Exoplanets in the Habitable Zone May Not Harbor Life
A University of Washington study finds that an Earth-sized planet needs a substantial surface water inventory—about 20–50% of Earth’s ocean volume—to maintain long-term habitability. On very dry worlds, the carbon cycle can break down, allowing CO2 to build up and heat the planet, potentially rendering it uninhabitable despite being in the habitable zone. Venus serves as a nearby analog, illustrating how small water differences can dramatically impact climate. The work suggests many desert-like exoplanets thought promising for life may actually be poor candidates and informs future observations and Venus missions.