Mercury may have shrunk up to 30 percent more than mapped

Gaku Nishiyama and colleagues compared global maps of Mercury's ridges and scarps with surface-roughness maps derived from NASA's MESSENGER data. Rougher, impact-churned regions show fewer visible shortening structures. The team argues that ejecta and broken terrain have buried part of the contraction record rather than proving that the planet cooled unevenly.

Correcting for those obscured features raises the estimated lifetime contraction by roughly 10 to 30 percent, to as much as 23 kilometers of lost diameter. That range is a model-based reconstruction, not a direct before-and-after measurement. BepiColombo's higher-resolution mapping could reveal smaller scarps and test whether even the revised estimate remains low.

Why it matters

A planet's accumulated shrinkage constrains its core, starting temperature, and thermal history. The correction also shows how preservation bias can make a complete-looking surface map systematically incomplete.

What the source establishes

Worth Revisiting peer-reviewed Geophysical Research Letters study. The additional contraction is inferred after correcting for obscuration; the upper estimate and interior implications await further testing.