Mercury's Contraction: A Widely Disputed Estimate, Not a Resolved Rate

Mercury's surface is marked by lobate scarps, high-relief ridges and wrinkle ridges that record planetary contraction, and the captured primary literature describes these as the dominant expression of a one-plate planet losing interior heat. A VICE article reports a study in Geophysical Research Letters finding the planet shriveling 10 to 30 percent faster than previously realized. ^{[2] [2] [1]}

That acceleration claim is not corroborated in the captured primary papers, which instead argue contraction estimates vary mainly because of mapping choices. A 2021 paper in Communications Earth & Environment assigns each landform a single principal fault and concludes Mercury's radius likely shrank by no more than 1 to 2 kilometers since the Late Heavy Bombardment, with a strong hemispheric asymmetry in contractional strain. ^{[2] [2] [2]}

The same paper reports that prior MESSENGER-era estimates reached roughly 4 to 7 kilometers of radius change, attributing those larger figures to grouping deformation-free relief with tectonic landforms and to assigning multiple faults to single structures. The paper itself records those earlier estimates as part of the literature, so the disagreement over how much Mercury has contracted remains unresolved in the captured evidence, not settled by the newer figure. ^{[2] [2] [3]}

A companion 2021 paper in Geophysical Research Letters also assumes one primary thrust fault per landform and finds the greatest contractional strain in crust about 50 to 60 kilometers thick, suggesting mantle flow helped localize lithosphere-penetrating thrusts rather than global contraction acting alone. VICE attributes the new study to lead author Gaku Nishiyama of the German Aerospace Center and reports that asteroid debris can bury shrinkage evidence, which is why estimates differ. ^{[3] [3] [1]}

VICE also states the European and Japanese BepiColombo spacecraft is slated to enter Mercury's orbit by November, while a NASA explainer last updated in October 2024 describes BepiColombo as a joint European-Japanese venture with two orbiters arriving in 2025. Planned timelines recorded at different dates cannot be reconciled from the captured material, and the BepiColombo observations that might clarify the rate are still in the future. ^{[1] [7]}