Mercury's metallic core occupies much of the planet, leaving a relatively thin rocky mantle around it.

Some polar crater floors never receive sunlight, allowing water ice to persist despite Mercury's scorching daytime surface.

As Mercury's interior cooled, the planet contracted, squeezing its crust into the long lobate scarps seen across its surface.

Because Mercury orbits closer to the Sun than Earth, the planet never strays far from the Sun in our sky.