Earth’s Secret Advantage: Why Most Alien Worlds May Be Too Dry for Life

A University of Washington study finds rocky exoplanets may need substantial surface water — about 20% to 50% of Earth’s ocean volume — to remain habitable long term.

Using models of arid worlds, researchers showed that too little water can break rainfall-driven carbon cycling, allowing carbon dioxide to accumulate and heat the planet.

The result is a narrower view of habitability: being in the habitable zone may not be enough if a planet cannot sustain climate-stabilizing water and carbon cycles.