Mercury (planet)
Mercury is one of four terrestrial planets in the Solar System, and is a rocky body like Earth. It is the smallest planet in the Solar System, with an equatorial radius of . Mercury is also smaller—albeit more massive—than the largest natural satellites in the Solar System, Ganymede and Titan. Mercury consists of approximately 70% metallic and 30% silicate material. Mercury's density is the second highest in the Solar System at 5.427 g/cm, only slightly less than Earth's density of 5.515 g/cm. If the effect of gravitational compression were to be factored out from both planets, the materials of which Mercury is made would be denser than those of Earth, with an uncompressed density of 5.3 g/cm versus Earth's 4.4 g/cm.
Gliese 581 planetary system
Gliese 581e is the innermost planet and, with a minimum mass of 1.7 Earth masses, is the least massive of the three. Discovered in 2009, it is also the most recent confirmed planet to have been discovered in this system. It takes 3.15 days to complete an orbit. Initial analyses suggested that the planet's orbit is quite elliptical but after correcting the radial velocity measurements for stellar activity, the data now indicate a circular orbit.