Meteoroids and Meteorites
The word meteor is derived from the Greek meteron, meaning something high up. Today, however, the term is used to describe the light phenomena produced by the entry of a meteoroid into Earth's atmosphere. A meteoroid is defined to be any solid object moving in interplanetary space that is much larger than an atom or a molecule, but smaller than a few meters in diameter. A visual meteor, or shooting star, is produced whenever a meteoroid is vaporized in Earth's upper atmosphere. If a meteoroid survives its passage through the atmosphere without being fully vaporized and falls to the ground, it is a called a meteorite.
Upon entering Earth's upper atmosphere, a meteoroid begins to collide with an ever-increasing number of air molecules. These collisions will both slow the meteoroid down and heat its surface layers. At the same time the meteoroid is being decelerated, that energy is transferred from the meteoroid to the surrounding air. Some of the meteoroid's lost energy is transformed into light; it is this light that we observe as a meteor. As the meteoroid continues its journey through the atmosphere, its surface layers become so hot that vaporization begins. Continued heating causes more and more surface mass to be lost in a process known as ablation, and ultimately the meteoroid is completely vaporized.
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