Meteors are cometary débris, too small and too friable to reach the surface of the Earth intact. Larger bodies, however, can survive the dash through the atmosphere, and land without being destroyed, though they may be fragmented. It may be helpful to give some definitions.

A meteoroid is defined by the IAU as ‘a solid object moving in interplanetary space, smaller than an asteroid and considerably larger than an atom’. This is all very well, but where exactly is the boundary between a meteoroid and an asteroid? The Royal Astronomical Society gives it as 10 m, but consider then the asteroid 2008 TN3, which impacted Earth on 7 October 2008. Its diameter was just about 10 metres, so that it could be classed either as a large meteoroid or a small asteroid; it was given an asteroid designation because it was followed telescopically well before it entered the atmosphere, exploded and broke into fragments. However, all the definitions could well be tightened up.

A meteorite is a body which has reached the Earth, or other planet, in recognisable form. If sufficiently large and dense, it may produce an impact crater. Note that the famous structure in Arizona is generally known as Meteor Crater; it really should be Meteorite Crater.

Meteorites and shooting-star meteors are very different. Most meteorites come from the asteroid belt, though some are believed to come from the Moon (see p. x) and others (the SNC meteorites) from Mars (see p. x).