Artist's impression of a large Meteor or "fireball" entering the Earth's atmosphere. Copyright Arizona Skies Meteorites 2009
The terms 'Meteoroid' and 'Asteroid' are both used to describe subplanetary sized rocky or metallic bodies, which have an independent orbit in space. The official definition of a meteoroid is "a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom." (International Astronomical Union). Asteroids are large meteoroids, typically over 10 meters in diameter. Because most meteoroids that enter the Earth's atmosphere are traveling at extremely high velocities (on the order of 7 to 46 miles per second!) they create extreme ram pressure and friction with the Earth's atmosphere when they enter it. This causes the meteoroid to rapidly heat and vaporize. The surrounding atmosphere is briefly ionized producing a brilliant incandescence known as a 'Meteor', 'fireball' or 'shooting star'. This frictional and compressional heating causes the vast majority of Meteoroids to burn up upon entry into the Earth's atmosphere. The few meteoroids that reach the surface of the earth are referred to as 'Meteorites'. A more general definition of 'meteorite' comes from Rubin and Grossman (Meteorite! 4 (3), p. 24-25, 1998): "A meteorite is a natural solid object that was transported by natural means from the body on which it formed to a region outside the dominant gravitational influence of that body and was later accreted by a natural body larger than itself."
Photo of the Asteroid Ida showing numerous impact craters (NASA)
Photo of the Holsinger meteorite- the largest iron meteorite ever found at Meteor Crater, Arizona.
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