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
Solar mass measurement, the solar mass came into use before the AU and the gravitational constant were precisely measured. This is because the relative mass of another planet in the Solar System or the combined mass of two binary stars can be calculated in units of Solar mass directly from the orbital radius and orbital period of the planet or stars using Kepler's third law, provided that orbital radius is measured in astronomical units and orbital period is measured in years. The mass of the Sun has been decreasing since the time it formed. This occurs through two processes in nearly equal