Most asteroids follow fairly regular paths in orbits between Mars and Jupiter. A small fraction, about one in a thousand, have evolved from their regular orbits by slow gravitational effects of the planets, mainly Jupiter, to travel in more elliptical orbits that cross the paths of other planets, including Earth. The first of these discovered was Eros, found in 1898, which crosses the orbit of Mars but not Earth. The first space mission dedicated primarily to visiting an asteroid was the Near Earth Asteroid Rendezvous (NEAR) mission (later renamed NEAR Shoemaker in honor of American astronomer Eugene Shoemaker), which orbited Eros for a year in 2000-2001, before touching down on its surface on February 12, 2001.

Cosmic impacts can cause major damage to Earth's surface and ecosystem. This meteorite crater is located near Winslow, Arizona.

Even in 1694, when Edmund Halley discovered that the orbit of the comet that bears...