Mercury is shrinking more than we thought

NASA’s MESSENGER spacecraft captured an image of Mercury’s surface on Oct. 6, 2008, revealing it is riddled with wrinkles, suggesting it once had a larger size and has shrunk over time. A new study estimates Mercury may have contracted 10% to 30% more than previously thought, losing nearly 12 miles (19 kilometers) in diameter since its formation. The study, published in Geophysical Research Letters, found that the roughest areas on Mercury have fewer visible wrinkles, indicating that impact debris may be obscuring signs of shrinkage. The team used maps of surface roughness and previous geologic evidence to estimate the amount of contraction, finding that missing features in rough areas could represent up to 10% to 30% more shrinkage than previously thought.

• "The study estimates Mercury's diameter has shrunk by 10% to 30% more than previously thought, which is about 12 miles (19 kilometers) in total."
• "The team used maps of surface roughness and previous geologic evidence to estimate the amount of contraction, finding that missing features in rough areas could represent up to 10% to 30% more shrinkage than previously thought."
• "The corrected amount of contraction makes sense to the researchers, suggesting that Mercury's interior is still shrinking, and observations are now more in step with physics-based predictions."

The findings suggest that Mercury’s interior is still shrinking, and the new data will help researchers better understand the planet’s evolution. The study highlights the importance of surface roughness in obscuring signs of contraction, and the updated estimates could still be an underestimate. The research is part of the BepiColombo mission, which will collect higher-resolution data on Mercury’s surface in 2026.

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