Study finds Mercury may have contracted up to 30% more than previously estimated
New analysis suggests Mercury's diameter could have decreased by as much as 14.5 miles since its formation, a larger shrinkage than earlier estimates, and upcoming BepiColombo mission will investigate further.
New research indicates that Mercury may have shrunk by up to 30% more than earlier calculations suggested, reducing its diameter by roughly 14.5 miles since the planet formed about 4.5 billion years ago. The study, published in Geophysical Research Letters, combined earlier geological maps with newer data that account for surface roughness caused by impact debris, allowing a more precise assessment of the planet's contraction.
Scientists have long linked Mercury's surface wrinkles to cooling of its interior, which causes the metallic core and mantle to contract. However, recent findings show that debris from asteroid and comet impacts has obscured many of these features, making the planet's total shrinkage harder to gauge.
"More shrinking means Mercury could have a larger metal core, less light elements like silicon mixed into the metal core, or a higher starting temperature," said lead author Gaku Nishiyama, a planetary scientist at the German Aerospace Center.
The authors note that the new estimate may still be conservative, as existing data from NASA's MESSENGER mission, which ended in 2015, lack the resolution to capture the smallest surface deformations. To address these gaps, the joint European Space Agency–Japan Aerospace Exploration Agency BepiColombo mission, scheduled to enter Mercury's orbit by the end of 2026, will carry two orbiters to study the planet's interior structure and evolutionary history.
The upcoming mission is expected to provide high-resolution measurements that could refine estimates of Mercury's core size, composition, and thermal history, shedding light on how the smallest terrestrial planet evolved in the harsh environment near the Sun.