In this
group can be put the small bodies of the Solar System- asteroids,
comets and meteors. They are really small, but in cosmic
dimensions. And in order to be clear about it from the very
beginning, we should know that one of the smallest asteroids that
science knows of, Hermes, is only 1 km long and has a volume of 520
000 000 cubic meters. He weighs a billion and a half tones- the
same as 300 Cheop’s pyramids would weigh.Asteroids are small planets, which are mainly situated in the area between Mars and Jupiter. Around 1700 of them are known to science (have their own names), but it is supposed that altogether they are more than 100 000. The biggest asteroid is called Cerebra and has a diameter of 770 km. There are some more with a diameter of 400-300-200 km and the others are no bigger than ten kilometers. The asteroids are stone and metal pieces often with irregular shapes. There is a supposition that they are what is left of a destroyed in the far away past planet, to which even a name was given- Phaeton.
Asteroid # 1566, called Ikar became very popular because of all bodies in the Solar System it passes at a nearest distance by the Sun (28,4 million kilometers). Every 19 years it passes periodically by the Earth at an average distance of 6,5 million kilometers.
Comets had a very bad fame in the past. They were thought of as reasons for wars and epidemics, Later they scared people with their big dimensions that are seen on the sky- people feared that if the Earth crashes into them, the “end of the world” would come.
Now science knows that comets (“stars with tails”) are actually celestial bodies that can do no harm to humans. They consist of a core (usually of ice and stones) around which the evaporating because of the sun rays gases form a head and the tens of millions long tail of very thin gases. These gases are repelled from the sunrays. This is why the tails of the comets are always in a direction opposite to the Sun. The Earth has many times passed through the tails of comets, of course, without us noticing this in any way. But even the meeting with the hard core does not threaten the Earth as a whole with any serious damage. It is supposed that the meteorite fallen on 30.07.1908 in the Siberian taiga was an icy core of a comet with a diameter of 100-120 m and a mass around a million tones.
The meteorites bombard the Earth’s atmosphere very often. These are really small stone or steel bodies, usually with a mass of some grams or parts of the gram. They move with high speeds- from 11,2 km/sec to 70 and more km/sec and burn in the high layers of the atmosphere. The phenomenon “ a shooting star” is called a meteor and the very piece, if it survives and falls on the surface of the Earth- a meteorite. In the area of the Solar System there are a lot of big groups of meteors called meteor flocks. It is supposed that many of them are pieces of former comets.
