Desert worlds outside our solar system are unlikely to host #life. This is because an Earth-sized #planet needs at least 20 to 50% of the #water in #Earth's #oceans to maintain a critical natural cycle that keeps water on the surface. Planetary #habitability hinges on the geologic #carbon cycle—a water-driven process that exchanges carbon between the #atmosphere and interior over millions of years, stabilizing surface temperatures. Carbon dioxide, which comes from #volcanoes in a natural system, accumulates in the atmosphere before falling back to Earth dissolved in rainwater. Rain erodes and chemically reacts with rocks on Earth's surface and runoff transports carbon to the ocean, where it sinks to the seafloor. Plate tectonics drives carbon-rich oceanic plates below continental land and millions of years later, carbon resurfaces as mountains form. However, if water levels drop too low for rainfall, carbon removal—from weathering—can't keep up with emissions from volcanic eruptions and carbon dioxide levels in the atmosphere spike, trapping water. Rising temperatures evaporate the remaining surface water, initiating runaway warming that makes the planet too hot to support life. That unfortunately makes arid planets, with little water and rainfall, within habitable zones unlikely to be good candidates for life. #astronomy #astrobiology #exoplanets https://phys.org/news/2026-04-planets-life-scientists-previously-thought.html Paper by White-Gianella et al. (2026): https://iopscience.iop.org/article/10.3847/PSJ/ae4faa