Crust of Mercury. Lacks weathering from liquids or an atmosphere and covered, maintains ancient craters, and covered in grey regolith like the Moon. Formed more like Mars than the moon in that heavy vulcanism was involved. Better shielded from Solar radiation than the Moon due to Magnetosphere. Comprised of three terrains, smooth plains, intermediate terrain, and low-reflective material. Thought to have contracted as the planet shrunk, forming rifts and tectonics, which could also represent a process of plate forming that never got going.