The word meteor means "phenomenon of the sky" and describes the light that occurs when a fragment of extraterrestrial matter enters the atmosphere. If the meteor does not completely disintegrate, each fragment that reaches the Earth's surface is called meteorite.
Instead, the word meteoroid It is applied to the particle itself, without reference to the phenomenon that occurs when it enters the atmosphere. There are many meteoroids and few meteorites.
Some of the meteorites that have been studied seem to have come from the Moon and others perhaps from Mars. Most, however, are fragments of asteroids or of kites.
There are also meteoroid currents formed by the decay of comet nuclei. When they coincide with the Earth, a meteor shower (or a storm, if it is very intense) originates, which can last a few days. They are popularly also known as Shooting Stars, although, naturally, they are not stars.
A large amount of meteoroids, several hundred tons of matter, enter the earth's atmosphere every day. But most are very small. Only the large reach the surface to become meteorites. The largest meteorite found (Hoba, in Namibia) weighs 60 tons.
The meteoroids enter the atmosphere at an average speed that ranges between 10 and 70 km / s. The small and medium ones slow down quickly up to a few hundred km / hour due to friction, and if they reach the earth's surface, they do so with little force. Only the big ones keep enough speed to produce a great impact and leave a crater.
There are three kinds of meteorites: lithosiderites They are formed by rocky materials and iron. They constitute only one percent of meteorites. Rocky meteorites, formed only by rocks, are the most abundant. Ferrous meteorites, 6% of the total, contain large amounts of iron.
The study of meteorites reveals interesting data. They are good examples of the primitive matter of the Solar System, although in some cases their properties have been altered.
The only iron that humans knew before inventing the forge came from meteorites. Terrestrial minerals that contain iron have no resistance. The extraterrestrial iron put us on the track of metallurgy.
Some catastrophes of the past may have been caused by meteorites, such as extinction of the Cretaceous dinosaurs, 65 million years ago, caused by the fall of a meteorite about 10 km in diameter. Or, at least, this is what some astronomers believe.
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