Mercury is shrinking

BBC : First noted by NASA’s Mariner 10 probe in the 1970s, scars on the surface of Mercury indicate where it has cracked and wrinkled due to contraction of the planet’s core. Mercury’s relatively huge iron center is covered only by a thin rocky crust, unlike Earth, whose core is encased by a more complex system of tectonic plates, crust, and mantle. As Mercury’s core cools, it has shrunk in volume, causing its crust to buckle and create enormous “lobate scarps,” mountainous structures hundreds of kilometers long and thousands of meters high. From data collected by NASA’s MESSENGER spacecraft, which has been orbiting the planet since 2011, Paul Byrne of the Carnegie Institution of Washington and colleagues have now been able to confirm that Mercury has decreased in radius by as much as 7 km since its crust solidified some 4 billion years ago.