Study Suggests Mercury May Have Shrunk Up to 30% More Than Previously Estimated
New analysis of MESSENGER data indicates that Mercury's radius could have decreased by as much as 11.6 km, a larger contraction than earlier estimates, and upcoming BepiColombo measurements aim to verify the finding.
A recent paper in Geophysical Research Letters argues that Mercury’s global contraction may be 10% to 30% greater than earlier calculations, implying a radius reduction of roughly 11.6 kilometers (7.2 miles). The authors, led by planetary scientist Gaku Nishiyama of the German Aerospace Center, used surface-roughness maps derived from NASA’s MESSENGER mission and noted that impact debris likely obscured many contraction-related ridges and cliffs.
"It made us think that there's a process obscuring shortening structures," Nishiyama said, referring to the possibility that crater ejecta hide evidence of the planet’s shrinkage.
Previous estimates placed Mercury’s radius change between 1 and 2 kilometers, with some studies suggesting up to 7 kilometers. The new calculations suggest a substantially larger contraction, which could indicate a larger metallic core, a lower proportion of light elements, or a higher initial temperature.
"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, director of the NASA Planetary Data System Geosciences Node.
The upcoming BepiColombo mission, now approaching Mercury after an eight-year cruise, will deploy two orbiters to obtain high-resolution topographic and gravity data for both hemispheres. Scientists expect these measurements to test the new contraction estimates and refine models of Mercury’s interior.
"Those new data will be key to testing whether this and other global contraction papers are right," Byrne added.
If confirmed, the findings would enhance understanding of Mercury’s evolution and provide comparative insights for other rocky planets, including Earth.