In the Solar system besides the large and small planets there are other heavenly bodies. First of all, it comets, which is also called the caudate stars. Is small, the size of several kilometers, blocks of stone and ice. According to the laws of Kepler's comet, like the other bodies of the Solar system, moving in elliptic orbits. But their orbits are very stretched, so that the most remote from the Sun point is usually far beyond the orbits of the most distant planet Pluto.

When the comet from the cold depths of space approaches the Sun, it becomes visible even to the naked eye. As it approaches the Sun, its strong radiation starts to heat the body of the comet and frozen gases evaporate. They expand, Shrouding the solid body of a comet, and forming its huge gas "top". Solar radiation is so strongly affects the gas that part of it is blown out of the head of the comet and forms the comet "tail"that accompanied her all the way near the Sun.

Most comets appears only once and then disappear forever in the depths of the Solar system, where they came from. But there are exceptions - periodic comets.

The sizes of the orbits of most comets thousands of times greater than the diameter of the planetary system. Near ataliev their orbits of comets are most of the time, so in the distant fringes of the Solar system there is a cloud of comets - the so-called Oort cloud. Its origin is connected, apparently, with the emission of gravitational icy bodies from the zone of giant planets during their education. The Oort cloud contains billions of cometary nuclei.

All comets during their movement in the area occupied planets orbit change under the action of gravity of the planets. Thus among comets that come from the periphery of the Oort cloud,about half acquires a hyperbolic orbit and is lost in interstellar space. Others, on the contrary, the sizes of the orbits are reduced, and they often return to the Sun. Changes orbits are particularly high during close approaches of comets with planets-giants. There are about 100 short-period comets approaching the Sun in a few years or decades, and therefore relatively quickly dissipate the substance of your kernel.

The orbits of comets cross with the orbits of the planets, so occasionally must occur collision of a comet with the planets. Part of the craters on the moon, mercury, Mars and other bodies formed as a result of the impacts of comet nuclei.