Wow: lobate scarps
What's a lobate scarp? Mercury, the smallest planet in the solar system (once Pluto was kicked out), has a molten core, but because that core is cooling the planet is shrinking and its crust which is solid has a number of fault thrusts which form great curved cliffs called lobate scarps.
According to a new report published today in Science, the planet has lost more than a mile in its diameter during its history.
Mercury is the only other terrestrial planet besides Earth in the solar system with a global magnetic field. Before the new data returned by Messenger, most scientists believed that Mercury's core was already solid, but now the evidence points to a core that is still molten so it seems possible that the forces creating those lobate scarps are still in action.
NASA launched Messenger seven years ago to fly by Mercury to help answer some of the questions about the planet and its features. In January it was close enough to start sending back new pictures of the surface and lots of data. There should be many more interesting discoveries as the planetary scientists read the data coming back from this very successful unmanned probe.