The names of the rocky planets in the Milky Way Galaxy are Mercury, Venus, Earth and Mars, the innermost planets closest to the sun. They are also called terrestrial or telluric planets because of their solid, rocky surfaces. Terrestrial and telluric originate from the Latin words for Earth, terra and tellus.
The composition of rocky, terrestrial or telluric planets consists of silicate rocks or metals. These planets differ from gas giants because of their solid surfaces and overall structure. The structure of a rocky planet includes a metallic core, usually iron, and a silicate mantle with canyons, craters, volcanoes, mountains and other typical features. Rocky planets also have secondary atmospheres produced by volcanic activity or comet impacts, while gas giants have primary atmospheres gained during the planet's original formation. Rocky planets also have similar densities to Earth.
The moons of some planets also have structures similar to a rocky planet. The Earth's moon has a small iron core and solid surface. Europa and lo, moons of Jupiter, both possess structures similar to rocky planets.
Most known extrasolar planets are gas giants because their size makes them easier to locate. The Kepler Mission located the first rocky extrasolar planet, Kepler-10b, in 2011.