New global imaging and topographic data from MESSENGER show that the innermost planet has contracted far more than previous estimates. The results are based on a global study of more than 5,900 geological landforms, such as curving cliff-like scarps and wrinkle ridges, that have resulted from the planet’s contraction as Mercury cooled. The findings, published online March 16, 2014, in Nature Geoscience, are key to understanding the planet’s thermal, tectonic, and volcanic history, and the structure of its unusually large metallic core.