Study suggests Mercury may have contracted up to 30% more than previously thought
Analysis of MESSENGER data indicates the innermost planet could have shrunk by as much as 7.2 miles, a larger reduction than earlier estimates, and upcoming BepiColombo observations aim to verify the findings.
New research using data from NASA's MESSENGER mission indicates that Mercury, the solar system's smallest planet, may have contracted up to 30% more than earlier studies suggested, corresponding to a radius reduction of about 7.2 miles. Lead author Gaku Nishiyama of the German Aerospace Center said debris from billions of years of impacts may have concealed many of the planet's surface cracks, leading to underestimates of its shrinkage.
The study mapped surface roughness globally and found fewer visible ridges in the roughest regions, implying that impact debris hides contraction features. Previous estimates placed Mercury's radius change between 0.6 and 4.3 miles; the new calculations suggest a larger contraction.
Scientists noted that a more accurate measurement of Mercury's shrinkage could refine models of its interior, including core size, composition, and thermal history. "Yet if we can accurately measure how much Mercury has contracted, we can make better estimates of its interior layering, the size and make-up of its core, its tectonic and volcanic histories, how its magnetic field is generated, and a whole lot more," wrote Dr. Paul Byrne of Washington University.
The upcoming BepiColombo mission, which will place two orbiters around Mercury by the end of the year, is expected to provide high-resolution topographic data across both hemispheres. Nishiyama, a member of the mission's science team, said the new measurements will allow scientists to test the latest contraction estimates. Dr. Kelsey Crane added that the instruments will detect gravity anomalies, crustal thickness, and surface composition, helping to build a more complete picture of Mercury's evolution.
While some researchers, such as Dr. Hannes Bernhardt of the University of Maryland, find the methodology sound, they note that a contraction of this magnitude might produce visible large-scale buckling, which has yet to be observed. Further analysis and future mission data are expected to clarify the extent of Mercury's shrinkage.