Mercury Shrinking 30% Faster Than Previously Believed, Scientists Find

11 September 2026 · Source balance: Centre

A new study from the German Aerospace Center's Institute of Space Research shows that Mercury may be shrinking faster than scientists previously estimated. The planet has lost up to 14 miles of its diameter — about 30 percent more contraction than earlier calculations indicated. Mercury has been cooling and shrinking for 4.5 billion years since its formation because its oversized iron core cools down, causing the planet to contract like a wrinkled raisin. Impact craters and debris on Mercury's surface had hidden evidence of this shrinkage, obscuring the true extent of the contraction. Researchers analyzed geological maps and surface roughness data to account for these hidden zones. The finding matters because understanding Mercury's cooling history helps scientists understand how all rocky planets, including the Moon and Mars, formed and evolved. The timing is significant as the European-Japanese BepiColombo spacecraft is expected to enter orbit around Mercury in November to conduct a fuller survey.