mercury is one of four inner planets in the solar system. it is a terrestrial planet like earth. it is the smallest planet in the solar system. it has a radius of . mercury is even smaller than some of the largest moons in the solar system, such as ganymede, the largest moon of jupiter and titan, the largest moon of saturn. however, it has in 2.2 times greater mass than ganymede and around 2 times heavier than titan. mercury is made of about 70% metallic and 30% silicate material. mercury has the second highest density in the solar system at 5.427 g/cm³, only a little bit less than earth’s.