The meteors we see in the night sky are very tiny pieces of space debris that flash as streaks of light when they vaporize in our atmosphere. The pieces of debris are called meteoroids, and these tiny pieces of matter are visible because they travel at amazingly high speeds, as fast as 25,000 miles (40,234 kilometers) per hour [source: American Meteor Society].
When meteors hit the Earth's atmosphere, the friction causes enough heat to boil and vaporize the meteoroids. Molecules from the atmosphere and the meteoroid break up and recombine into what we see as a trail of light. The chunks that reach the Earth are really only the remains of meteoroids -- called meteorites -- that must have been at least the size of marbles. The particles are usually tiny, and they escape burning up and vaporizing because they're very light and travel more slowly through the atmosphere than larger meteoroids, thus generating less heat. If you find a more substantial meteorite on the ground, it probably came from a larger meteoroid -- maybe even the size of a basketball.
Some have speculated that a meteorite can actually boil water when it falls to Earth, but this is probably a myth. Many people who witnessed a 2007 meteorite crash in Peru claimed to have witnessed boiling water in the crater that resulted [source: Nizza]. Some scientists have speculated that as a result of a geothermal event, gases from inside the Earth boiled the water. Another idea is that the meteorite was so hot upon impact that it caused the water to boil. Yet another possibility is that the locals simply didn't report what they saw accurately. Other questions about this meteorite crash, such as the reason that many locals became ill, were eventually answered. Why or even whether there was boiling water in the crater remains a mystery, though, and scientists are split on whether meteorites are even hot when they hit the Earth [source: Carter].
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