Mercury Is Shrinking Faster Than Scientists Thought

Mercury, the smallest planet in the solar system, has contracted significantly more than scientists previously estimated, according to a new study published Thursday, September 10, 2026, in the journal Geophysical Research Letters. The research, led by planetary scientist Gaku Nishiyama, concludes that the planet's total shrinkage since its formation roughly 4.5 billion years ago could be up to 30 percent greater than earlier calculations suggested, with the planet losing as much as 23 kilometers, or about 14.5 miles, from its diameter. Previous estimates had put the loss at a range of 4 to 16 kilometers. Mercury has been cooling since its violent birth, when repeated collisions between rocks and asteroids orbiting the young sun generated enormous heat. As the planet's interior released that heat into space, it contracted, forcing its rocky outer layers to buckle and crack. This process created steep cliffs known as scarps and raised ridges across the surface, features scientists have long used to measure how much the planet has shrunk.