Overview
- A DLR team led by Gaku Nishiyama published a paper in Geophysical Research Letters on Sept. 11, 2026, reporting that Mercury’s diameter may have decreased by up to 23 kilometers since its formation.
- The authors base the larger estimate on the idea that many shortening features such as scarps and ridges have been buried by material thrown out by impacts and so were missed in earlier counts.
- Previous estimates using NASA’s MESSENGER maps put total shrinkage at roughly 4 to 16 kilometers, and the new analysis raises that figure by about 10% to 30 percent.
- MESSENGER data reliably resolve features about 5 kilometers or larger, which could explain why smaller or buried contractional structures went undetected, and BepiColombo’s BELA laser altimeter is expected to test this when the mission begins science operations in April 2027 after orbit insertion on Nov. 21, 2026.
- Confirming more contraction would tighten constraints on Mercury’s thermal history and core cooling, change models of rocky-planet evolution, and give researchers a clearer roadmap for where to look for hidden geological evidence.