12/23/2025
Mercury is actually getting smaller. Over billions of years, the planet’s interior has been slowly cooling. As its massive iron core loses heat, it contracts slightly, reducing Mercury’s overall radius by an estimated 4–7 kilometers (2–4 miles) since its formation. That may sound minor, but on a world with no plate tectonics and a brittle crust, the consequences are written directly across the surface.
With nowhere for the crust to release that stress, Mercury buckles and fractures. The result is a network of enormous cliffs, known as lobate scarps, some rising nearly two miles high and stretching for hundreds of miles. Many of these features cut across impact craters, showing that they formed long after the surface itself — evidence that Mercury isn’t a dead, frozen relic, but a planet that has continued to change deep into its geological past.
Mercury challenges the idea that small worlds go quiet quickly. Even the smallest planet in our solar system is still responding to forces deep within its core. If you want more hidden truths about the planets we think we already know, follow us.
