Mercury, the smallest and innermost planet of our solar system, is contracting more rapidly than decades of scientific modeling had anticipated, compelling researchers to revisit long-held assumptions about how rocky worlds cool, shrink, and age over geological time. The discovery, drawn from careful analysis of the planet's surface formations and gravitational profile, suggests that Mercury's interior has shed more heat — and more volume — than prior estimates allowed. In recalibrating one small world's history, scientists find themselves rethinking the broader story of how terrestrial planet