1. An asteroid is small solar system body in orbit around the sun, especially in the inner solar system. It is smaller than planet but larger than meteorite. Asteroid that is on collision course with earth is called meterorite. The distinction between asteroid and comet is made on visual appearance. Comet shows a perceptible coma while asteroid does not.
2. An asteroid, called 2010GA6 was close by earth on 8 April 2010,but posed no threat of crashing into our planet.
3. There are dozens fo unknown asteroids that fily close by earth from time to time. But majority of them are not hazardous to the earth.
4. The film is Deep Impact.