Overview
- University of Washington researchers, whose paper appeared Monday in the Planetary Science Journal, report that Earth‑size planets need roughly 20%–50% of Earth’s ocean water to keep climate stable over billions of years.
- With too little water, rain‑driven rock weathering cannot remove volcanic carbon dioxide fast enough, so heat builds, water boils away, and the planet tips into a runaway greenhouse state.
- The team used a coupled model that tracks carbon and water between a planet’s surface and interior, testing 18 factors including atmospheric escape, volcanic outgassing, land coverage, rock chemistry, rainfall runoff, and evaporation.
- The results suggest many dry worlds inside the classic habitable zone are poor bets for biosignature searches, though systems like TRAPPIST‑1 and future spectra from NASA’s proposed Habitable Worlds Observatory could probe surface water and land fraction.
- Venus is highlighted as a nearby test case, as slightly less starting water could have unbalanced its carbon cycle; upcoming Venus missions may help validate these predictions, and the study cites support from the National Science Foundation, NASA’s Astrobiology Program, and the Alfred P. Sloan Foundation.