The smallest planet in the solar system has undergone significant shrinkage, consuming 30 percent more than scientists had previously estimated. Mercury, which orbits closest to the Sun, is a small rocky world that has continuously leaked heat into space since its formation 4.5 billion years ago. As its heavy iron core cools, the entire planet shrinks, like a grape turning into a raisin in the sun. Its outer crust warps and cracks around it, but on a planetary scale, those surface wrinkles translate into enormous cliffs and mountain ridges. A new study reveals that Mercury has lost up to 14.5 miles of its diameter since its birth. It may not seem like much until you realize that the planet is only 3,000 miles wide in total. For decades, researchers may have underestimated the planet’s shrinkage because the rugged terrain obscured the true extent of the damage. “Thirty percent is a bit surprising, but the corrected amount of shrinkage actually makes sense to me,” Gaku Nishiyama, a planetary scientist at the German Aerospace Center Institute for Space Research and lead author of the study, said in a statement. SEE ALSO: Astronomer proposes surprising reason why we don’t have a super Earth. A barrage of meteors hits the surface of Mercury, cratering the earth and sending giant shattered rocks across the planet. The debris appears to create an expanse of fresh gravel, hiding the planet’s wrinkles. While testing Nishiyama’s hypothesis, a team of researchers discovered a clear pattern: bumpy regions contained the fewest visible wrinkles. Around major impacts, such as the huge Rachmaninoff crater, tectonic cracks almost completely disappeared under thick layers of debris. Crushable speed of light “We compared a global map of Mercury’s surface roughness with maps of shortening and shrinking structures,” Nishiyama said. “Mercury appears to have shrunk considerably more than the visible tectonic record alone suggested.” After taking these hidden features into account, the researchers recalculated Mercury’s total shrinkage. The results were published in the journal Geophysical Research Letters this week. Want more science and technology news delivered straight to your inbox? Sign up for Mashable’s Light Speed newsletter or receive push alerts from Mashable today. For scientists, the findings could resolve a long-standing tension. Previous estimates suggested much smaller shrinkage than physics predicted, leaving researchers uneasy with their understanding of how planets cool. By correcting the math, astronomers can uncover clues about Mercury’s original temperature and how other increasingly smaller rocky worlds, like our own moon, evolve over time. NASA’s Messenger spacecraft captured Rachmaninoff Crater, a double-ring basin about 180 miles wide, on Mercury in 2009. Credit: NASA/JHUAPL/CIW A faster rate of contraction may mean Mercury contains a much larger metallic core containing fewer light elements, such as silicon, than previously thought. This is important because a larger iron core would rewrite what scientists know about the birth of Mercury. More metal would strongly suggest that the planet survived a catastrophic collision with another body in its ancient history, an event that could have destroyed most of its rocky crust. A large core could also explain how such a small world kept its interior moving, a necessity for its global magnetic field. Scientists won’t have to wait long to verify the team’s work with new data. The BepiColombo spacecraft, a joint mission of the European Space Agency and Japan’s JAXA, is on the last leg of its space journey to Mercury. It is expected to enter orbit around the planet in November. Equipped with advanced lasers, BepiColombo will scan Mercury’s surface to detect fine details in its surface features that previous space missions missed. Only two missions, NASA’s Mariner 10 and Messenger, have visited the planet before, and only Messenger has ever orbited it.
