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A study published on 10 September 2026 in Geophysical Research Letters (AGU) finds that Mercury may have contracted 10-30% more than earlier thought.
The planet's diameter may have shrunk by up to 23 km since it formed, against earlier estimates of about 4-16 km.
Debris from impact craters buried many of the wrinkle-like fault features that record the shrinking, so earlier counts missed them.
The lead author, Gaku Nishiyama, is from the German Aerospace Center (DLR). ESA-JAXA's BepiColombo, due to enter Mercury orbit on 21 November 2026, may reveal the smaller hidden features.
As Mercury's interior cooled, the planet shrank and its rigid crust buckled. The crust broke along thrust faults, forming long cliffs (lobate scarps) and wrinkle ridges. Measuring these features shows how much the planet contracted.
Simple Analogy: Like skin wrinkling on an apple as it dries and shrinks.
Germany's space agency; its Institute of Space Research led the study
Publishes Geophysical Research Letters
Joint partners in the BepiColombo mission to Mercury
NASA's Mariner 10 makes the first flybys and images lobate scarps
NASA's MESSENGER (launched 2004) becomes the first spacecraft to orbit Mercury
MESSENGER ends its mission with a planned impact on Mercury
ESA-JAXA BepiColombo launched from Kourou, French Guiana
BepiColombo scheduled to enter Mercury orbit. Its MPO (ESA) and Mio (JAXA) orbiters separate on 9-10 Dec 2026
BepiColombo's science phase due to begin
Prelims > Science & Tech > Space missions; Geography > Solar System
General Science > Solar System
A long, curving cliff formed by a thrust fault as a planet's crust shortens during contraction.
A rocky planet: Mercury, Venus, Earth and Mars.
Time for the Sun to return to the same spot in a planet's sky; 176 Earth days on Mercury.