Friday, February 15, 2013
Also called minor planet, an asteroid is any of the thousands of small celestial bodies, measuring from 500 miles to less than one mile in diameter, that drift in outer space. In the Solar System, asteroids revolve about the Sun in orbits that lie mostly between those of Mars and Jupiter. Contrary to planets and satellites that are spherical, they are irregular in shape, with most of them being composed of nickel iron and silicates. Many of them have hit the Earth and other planets of the Solar System in the past.