Mercury is shrinking much more than scientists realized

The solar system's smallest planet has suffered significant shrinkage, drawing up 30 percent more than scientists even previously estimated. Mercury, which orbits closest to the sun, is a tiny rocky world that has continuously leaked heat into space since its sizzly formation 4.5 billion years ago. As its heavy iron core cools, the entire planet shrinks, like a grape transforming into a raisin in the sun. Its outer crust buckles and cracks around it, but on a planet scale, those surface wrinkles translate into huge cliffs and mountainous ridges. A new study reveals Mercury has lost up to 14.5 miles of its diameter since birth. That might not seem like much until you realize that the planet is only 3,000 miles wide overall. For decades, researchers may have underestimated the planet's contraction because the rough terrain was obscuring the true extent of the damage.