Page 188 - Science Class 08
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Asteroids : Asteroids are rocky worlds revolving Meteors and Meteorites : Meteors are very
around the sun that are too small to be called small bodies whose eccentric orbits bring them
planets. They are also known as planetoids or into collision with the earth. When they enter
minor planets. There are millions of asteroids, the earth’s atmosphere at very high speed, the
ranging in size from hundreds of miles to heat produced by their fric on, against the
several feet across. In total, the mass of all the atmospheric air, causes them to get vapourised
asteroids is less than that of the earth’s moon. and produce a brilliant trail. That’s why
meteors are also called shoo ng star. We may
some mes see these shoo ng stars when the
sky is clear and the moon is not there. Most of
the meteors get fragmented and disappear in
the earth’s atmosphere, however, a few of
them survive and reach the earth’s surface.
These meteors are known as meteorites.
Asteroid
Despite their size, asteroids can be dangerous.
Many have hit the earth in the past and more
will crash into our planet in the future. That’s
one reason scien sts study asteroids and are
eager to learn more about their numbers,
orbits and physical characteris cs.
Most asteroids are in a band between the Meteor
orbits of Mars and Jupiter. The diameters of Comets : Comets are space objects made of
asteroids range from less than 16 km to more minerals, dust, gases and ice par cles that
than 160 km. The average distance between orbits the sun. They look like the fuzzy stars.
two asteroids is probably about 6 million km. Comets is a La n word meaning long-haired. A
Their origin is not known, but there are three comet consists of a head and a tail. The head
scien fic theories for their forma on. One contains most of the ma er of the comet. A
theory states that asteroids may be pieces of comet’s long tail of dust and gases extends into
what was once a single planet. When its orbit space for millions of kilometers. The tail reflects
carried the planet close to Jupiter, the planet sunlight which make it visible.
sha ered. A second theory states that
asteroids are the pieces of two planets that
collided and smashed into fragments. A third
theory states that asteroids are bits of ma er
that did not fuse to form a planet.
The largest known asteroid is ‘ceres’ which is
about 800 km in diameter and it was
discovered on January 1, 1801.
Comet
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