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Mercury Is Shrinking?!


Mercury is cooling. It has been for an untold number of years, and scientists believe the shrinking may have been going on for billions. Even though there’s no planet closer to the Sun, Mercury’s interior is cooling down. And as the internal heat seeps out into the universe, the core of rock and metal contracts. As it does so, there’s progressively less area for the crust to cover.

A new paper published in Nature Geoscience says that not only has Mercury been shrinking for a very, very long time of time (something we already knew), it continues to shrink to this day. On top of that, the authors claim that we can expect the contracting of Mercury to continue. “Until now, evidence has been sparse,” David Rothery, professor of planetary geosciences at the Open University and co-leader of the European Space Agency’s Mercury Surface and Composition Working Group, wrote in an article for The Conversation. “But our team found unambiguous signs that many scarps [ramp-like slopes showing the shrinkage] have continued to move in geologically recent times, even if they were initiated billions of years ago.” According to the study, this action—along with the widespread distribution of these scarps—is consistent with a slowly cooling planetary interior enduring prolonged global contraction. “Because Mercury’s interior is shrinking, its surface has progressively less area to cover,” Rothery wrote. “It responds to this by developing ‘thrust faults’—where one tract of terrain gets pushed over the adjacent terrain.” Scientists first saw evidence of this thanks to a 1974 Mariner 10 mission. Then, from 2011 to 2015, the Messenger mission offered up more images of the faults and scarps. “It was possible to deduce that gently dipping geological faults, known as thrusts, approach the surface below each scarp and are a response to Mercury having shrunk,” Rothery wrote.

In all, the Mercury’s radius has shriveled by over four miles since its formation. Along with the thrust faults and scarps, the team discovered grabens—depressed blocks of crust, some nearly 500 feet deep and tens of miles in length—which are adding to the shrinkage. By studying Mercury and understanding the interplay of these geological features, the team “calculated that the majority of grabens are less than about 300 million years old,” Rothery writes. That points to recent movements. Using the images from Messenger, researchers located scarps topped with small grabens, giving the team reason to believe this movement is recent and ongoing. A planned BepiColombo mission to orbit Mercury should yield further information now that the team knows where to look. Not only will we get a clearer view of the geological movement through enhanced imaging, but the camera’s quality may highlight boulder tracks that could offer evidence of recent quakes. Mercury is shrinking, and scientists will stay on the watch to learn the details of both what that looks like and what it means for the planet. Rothery, for one, is “looking forward to finding out.”

Source: https://www.popularmechanics.com/space/solar-system/a45431594/why-is-mercury-shrinking/