In ancient Greek mythology, Mercury is a fast footed god. In the realm of astronomy, mercury is a planet. In the field of metallurgy, Mercury is a metal. While mercury itself is also a metal, mercury the planet doesn’t contain mercury the metal in any substantial amounts. In fact, planet mercury is rich in iron. Mercury turns out to be the densest of the terrestrial planets. Terrestrial planets are the first four planets located closest to the sun; they look like earth, hence called terrestrial or earth like planets. Planet Mercury is made of about 60 percent iron—twice as much as Earth has—and 40 percent other minerals. Why does it have so much iron is a mystery planetary scientists are still working to solve.