A comet is a small body composed of rock and ice that orbits the Sun. A comet's tail of ice particles can stretch for millions of kilometers behind it. Comets originate in the outer regions of the solar system and have a wide range of orbital periods, up to a thousand years long. Scientists have identified thousands of comets, but this is just a fraction of the total number that exist.
Asteroids are irregularly shaped, rocky bodies that circle the Sun. They are found mostly in an area between Mars and Jupiter called the asteroid belt. Asteroids range in size from quite small to 100 kilometers in diameter. There are over 500,000 known asteroids.
Meteoroids are smaller pieces of rock that have originated from asteroids. A streak of light called a meteor is seen when a meteoroid enters and burns in the Earth's atmosphere. When a meteoroid strikes Earth, it is called a meteorite. Meteor Crater in Arizona shows the impact and size of meteorite collision.