Overview
- A peer-reviewed paper by Gaku Nishiyama and colleagues published on Friday reports that correcting for surface roughness raises Mercury’s estimated radial shrinkage from about 8.3 km to 11.6 km, which corresponds to a diameter loss of up to roughly 23 km.
- The team compared global maps of surface roughness with maps of known contractional landforms to identify regions where impact ejecta and heavily cratered terrain likely hide or erase tectonic ‘wrinkles’.
- By accounting for those masked areas the researchers reduced a prior mismatch between the expected roughly uniform global cooling and the uneven distribution of mapped contractional faults.
- A larger contraction changes constraints on Mercury’s interior because greater shrinkage implies a bigger metal core, fewer light elements in that core, or a hotter initial state, which alters thermal-evolution models used by planetary scientists.
- The result is provisional because NASA’s MESSENGER data miss smaller-scale features, and ESA/JAXA’s BepiColombo mission will test and refine the estimate with higher-resolution topography when it arrives in orbit on 21 November 2026.