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Asteroids, Meteors and Meteorites
Planet and their moons are major members of the solar system. There are minor members called asteroids. An asteroid is an irregular lump of rock that orbits the sun. They are in large numbers in a belt between the orbits of mars and Jupiter. They lie at a distance of 2.2 to 3.3 au. This belt is estimated to have some 40,000 to 50,000 asteroids. Some of them are so tiny that their diameter cannot be measured with the help of prevalent techniques. Ceres, the biggest of these, has a diameter of 1003 to 1040 km. it was discovered in 1801.4 Vesta, the brightest asteroid, is the only asteroid that can be seen with the naked eye. Its diameter is 555 km. Hermes, another asteroid which was at a distance of 7, 80,000 km. from the earth, is now extinct.
It is not known how asteroids came into being. Some astronomers think that they are broken pieces of some planet which once existed between mars and Jupiter. Other considers them as pieces broken off mars and Jupiter themselves. Some asteroids may be chips and fragments of comets.
Meteors and Meteorites
Meteors and Meteorites
Sometimes we see a luminous object moving very fast across the sky leaving a streak of light behind it and which suddenly disappears. It is generally called a falling star. But we know that stars never fall. These tiny bodies which appear to fall are not stars but meteors. They enter the earth’s atmosphere with a tremendous speed and burn up as a result of frictional heating. This heat causes the meteoroid to glow. Meteors also are members of the solar system.
Meteors do not reach the earth. Most of them either burn up and disappear on their journey or are converted into vapor and dust where a meteor does not burn up completely, it falls down and hits the earth. When the meteoroid hits the earth’s surface, it is called a meteorite.
Craters have been formed on the surface of the moon. Mars and Mercury as a result of meteorites hitting them. The biggest such crater on earth in Arizona was created by some meteorite. Its diameter is 1.265 meters and depth 175 meters.
Around 25 million visible meteors are estimated to enter earth’s atmosphere everyday. They have a speed of 35.95 km. per second. An ordinary meteor takes approximately one second to convert itself into vapor. About 500 meteorites hit the surface of the earth in a year’s period.
The largest known meteorite found in 1920 at Hoba west near grootfontein at south West Africa weighted about 60,000 kg. It hit the ground during pre-historic age.
Calcutta museum has some meteorites as exhibits.