Mercury Shrinks Up to 30% More Than Previously Estimated

Mercury’s heavily cratered surface shows a pattern of concentric wrinkles that scientists have long associated with the planet’s cooling and shrinking. A new study, published in the journal *Nature Geoscience*, argues that the planet’s contraction has been substantially underestimated. By re‑examining high‑resolution imagery from NASA’s MESSENGER mission and accounting for the masking effect of impact debris, the researchers estimate that Mercury has lost between 10 % and 30 % more of its original diameter than previously believed—roughly 12 miles (19 kilometres) since its formation.

The analysis shows that the debris from numerous impact craters has obscured the subtle tectonic features that record the planet’s size change. Earlier models, which relied on visible wrinkle patterns alone, had suggested a contraction of about 8–10 % of Mercury’s diameter. The new work incorporates a statistical correction for crater coverage, revealing that the planet’s lithosphere has contracted far more than the visible scars would indicate. This finding has implications for models of Mercury’s interior evolution, the thermal history of the inner Solar System, and the processes that govern planetary cooling.

If Mercury indeed shrank by nearly a dozen miles, the planet’s core and mantle dynamics may have been more vigorous than current theories predict. The study underscores the importance of considering impact‑related masking when interpreting planetary surface features, and it invites a reassessment of the thermal and tectonic histories of other terrestrial bodies that have undergone similar cooling.