Scientists have uncovered evidence that Mercury, the planet closest to the Sun, may have contracted significantly more than earlier models indicated. The findings, detailed in a recent issue of Geophysical Research Letters, propose that the planet’s diameter could be up to 14.5 miles (23 km) smaller than the current estimate of 2.5 to 10 miles.
Why the New Estimate Matters
Mercury’s surface is riddled with wrinkles—tectonic features known as shortening structures—that record the planet’s cooling and contraction over billions of years. Lead author Gaku Nishiyama of the German Aerospace Center (DLR) explains that these wrinkles are harder to detect in regions covered by impact debris, which masks the signs of shrinkage.
By combining existing maps of contraction evidence with new maps of surface roughness, the research team showed that the roughest areas have fewer visible wrinkles. This suggests that impact debris has hidden a portion of the planet’s contraction, leading to an under‑count of the total shrinkage.
Implications for Mercury’s Interior
If Mercury has indeed shrunk 10% to 30% more than previously thought, the planet’s internal composition may need to be reassessed. A larger metal core with fewer light elements such as silicon, or a higher initial temperature, could explain the additional contraction.
“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,” Nishiyama said.
Future Observations
The study’s conclusions arrive just before ESA’s BepiColombo mission, the third spacecraft ever sent to Mercury, begins its high‑resolution survey later this year. Data from BepiColombo are expected to provide clearer images of scarps, ridges, and impact craters, potentially confirming the revised contraction estimates.
“We hope the new data will reveal scarps, ridges and impact craters in more detail than ever before,” Nishiyama added.
Original reporting: KTBS 3 (Shreveport) — read the source article.
