Mercury is still shrinking as its cooling core cracks the planet's thin crust

Mercury is the smallest planet in the Solar System, only slightly larger than Earth's Moon, but what lies beneath its battered surface is anything but small. Its metallic core stretches out to nearly 85 per cent of the planet's total radius, leaving behind a rocky shell so thin it barely qualifies as a shell at all. Over billions of years, as that core has cooled, the whole planet has contracted, and its brittle crust has had to absorb the strain, buckling into cliffs and ridges hundreds of kilometres long. It is this lopsided internal structure, an enormous core wrapped in a wafer of rock, that explains much of what makes Mercury such an odd world.How scientists discovered Mercury is still shrinkingPerhaps the more striking part is that this is not something that happened and stopped. Images taken during MESSENGER's final, lower-altitude orbits turned up small fault scarps far younger than the large ones discovered decades earlier, evidence that Mercury is still shrinking and still tectonically active right now.A study published in Nature Geoscience, titled ‘Widespread small grabens consistent with recent tectonism on Mercury’, researchers catalogued 190 grabens, narrow strips of ...