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Study Finds Mercury Shrank 30% More Than Expected

scienceSep 15, 2026·296 words·3 min read

Mercury, the smallest planet in our solar system, may have shrunk about 30% more than scientists thought, according to a new study. The research was led by planetary scientist Gaku Nishiyama of the German Aerospace Center, who also works with Hokkaido University. The planet may have lost as much as 14 miles (23 kilometers) in diameter.

Mercury has been getting smaller for 4.5 billion years. Its hot iron center, called the core, is slowly cooling. As it cools, the planet gets smaller, and lines like wrinkles appear on the surface. Scientists count these wrinkles to measure the change. But the study found that many wrinkles may be hidden because space rocks hit the planet and covered them. The team used pictures from MESSENGER, a spacecraft from NASA (the US space agency), to make a detailed map.

Mercury is hard to study because it is very close to the Sun and very hot. Only two spacecraft have visited it so far. In November, a European and Japanese spacecraft called BepiColombo should start to orbit, or travel around, the planet. It will help check how much Mercury has shrunk. "We are quite excited," Nishiyama said.

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