Solar System all have impact craters and tectonic surface features, such as rift valleys and volcanoes. The term "inner planet" should not be confused with "inferior planet", which designates those planets that are closer to the Sun than Earth is (i.e. Mercury and Venus). Asteroids except for the largest, Ceres, are classified as small Solar System bodies and are composed mainly of refractory rocky and metallic minerals, with some ice. They range from a few metres to hundreds of kilometres in size. Asteroids smaller than one meter are usually called meteoroids and micrometeoroids (grain-sized), depending on different, somewhat arbitrary definitions. The asteroid
Terraforming of Venus intervention for the purpose of building colossal mountains on Venus to serve as islands of colonization in the skies of Venus. Since Venus only has a fraction of the water on earth (less than half the earth's water content in the atmosphere, and none on the surface), water would have to be introduced either by the aforementioned method of introduction of hydrogen, or from some other extraplanetary source. Paul Birch suggests the possibility of colliding Venus with one of the ice moons from the outer solar systems, thereby bringing in all the water needed for terraformation in one go. This