Mercury Is Slowly Shrinking
Mercury may have become about 38 kilometers narrower since it formed as its cooling interior slowly contracts.
9/16/2026Mercury is literally shrinking. The inside of the Solar System’s smallest planet has been cooling for billions of years. As its temperature drops, its volume gets smaller. The surface has to adjust, so it wrinkles and cracks, creating huge cliffs and structures that look like wrinkles on drying fruit.
A new analysis of data from the MESSENGER spacecraft suggests that the scale of this process may have been underestimated by as much as 10–30 percent.
Since Mercury formed, its diameter may have decreased by about 38 kilometers in total, equal to losing about 19 kilometers of radius. Its average shrinking rate was at least 2.7 kilometers per billion years.
Learning more about this process could reveal more about the planet’s giant metallic core. The results suggest that it may contain fewer light elements and have a larger inner core than previously thought. The BepiColombo mission is expected to improve measurements and create more accurate maps of Mercury’s Martian surface.