Sign up to see the future, today Can’t-miss innovations from the cutting edge of science and technology Scientists say the planet Mercury has been actively shrinking over the billions of years it has orbited the Sun, a process that is leaving cracked wrinkles like an old apple. At just one-third the size of Earth, it is already the smallest planet in our solar system (it is larger than Pluto, but Pluto is no longer classified as a planet), a title it is sure to hold as its physical size continues to decline. Now, as detailed in a new paper from a team of scientists at the German Aerospace Center (DLR) Space Research Institute, the strange planet’s shrinkage could be occurring at an even faster rate than expected, losing up to 14.5 miles in total diameter since it formed billions of years ago. This is between ten and 30 percent more than previously thought. Scientists suggest that debris from impact craters may have masked this accelerated contraction, a process largely believed to be the result of Mercury running out of heat, “like a balloon left out in the cold,” according to an accompanying press release. The findings could help scientists get a better idea of what’s happening inside the planet and how it evolved over time. “Greater shrinkage means Mercury could have a larger metallic core, fewer light elements like silicon mixed into the metallic core, or a higher initial temperature,” DLR planetary scientist Gaku Nishiyama explained in a statement. “Every planet is an odd duckling that has a story to tell,” planetary geoscientist Sam Birch of Brown University, who was not involved in the study, told the New York Times. “If you can understand how fast Mercury is shrinking, you can understand how fast it’s cooling, what size it started at, and what it’s made of.” Mercury’s outermost layer of hard rock has been resisting (or at least trying to resist) this deflation, causing its surface to crack and “wrinkle.” It is a rugged surface lined with steep cliffs known as escarpments, as well as ridges that make it difficult to get a broader idea of how much it is shrinking overall. By adding previous maps of the planet’s surface, the team found evidence that rougher areas have fewer wrinkles, suggesting that debris from the impact is “obscuring the shortened structures,” according to Nishiyama. Their newly revised contraction rates also better reflect earlier physics-based predictions. Fortunately, we’re about to take a closer look at the deflating planet. The European Space Agency and Japan Aerospace Exploration Agency’s BepiColombo mission, which launched in 2018, will enter Mercury orbit in November, if all goes according to plan, becoming the second spacecraft to do so in human history. More on Mercury: Mercury has a layer of diamonds eleven miles thick, scientists discover
