Comets fascinate the human mind since ancient people first noticed the white tail streaking through the night starry sky. We remember the date when the comet flies past the Earth once a century or even less often and remember all our lives. In the middle ages in Europe, the appearance of comets was often linked to various natural disasters and diseases. In religion, these heavenly bodies also play an important role. For example, in the New Testament, the comet heralded the birth of Christ.
Astronomers find comets also interesting and fascinating space objects, because they are witnesses of great historical events and even carry evidence of them.
The comet is a relatively small object in our solar system, usually having a diameter of several kilometers. Sometimes called “dirty snowballs” because of their component substances. Usually comets are composed of the following four elements:
Ice (water, ammonia, methane, carbon dioxide)
Some organic materials (e.g., resin)
Rocky ground (optional)
Scientists assume that the comet consists of a material of the early solar system. They were formed during the time of the formation of the Sun from dust and gases, which formed a huge cloud okrugnaja luminaries. Some of this material has been expended on the formation of the 8 planets, and some remained in the form of two clouds of debris and dust far around the Sun:
The Oort cloud is a spherical education in a distance of more than 7500 billion km.
The Kuiper belt is a region in the plane of the Solar system beyond the orbit of Pluto.
According to the theory, the comet initially rotate in a spherical orbit around the Sun in one of these areas. However, under the influence of any external forces such tranquil situation may change, and some objects may leave its refuge. For example, when another star passes by the Solar system and its gravity will affect the Oort cloud or the Kuiper belt, any meteorite could change its orbit from spherical to elliptical with a focus at the Sun.
Depending on the speed of movement and length of orbit rotation period of the comet can be from several tens, to several hundreds or even thousands of years.
Compulsory component of any meteorite is ice. It is he who gives the comet its main attribute is the tail. However, it is not constant and only occurs when the comet flies close to the Sun (less than 1 billion km), because it is a cloud of gases substances constituting the comet, and dust. Moreover, the direction of the tail is always away from the Sun and the longer the tail, the closer it is to the sun. The tail often has a slightly curved shape, because the velocity of a comet is comparable to the speed of release of substances from its core.
Also when the comet is near the Sun it becomes another visible component – a halo around Agra. It consists of water vapor, ammonia, carbon dioxide and dust. And this cloud is heated much stronger than the core and may reach the diameter of Jupiter or Saturn (100,000 km).
The comet has another, second invisible halo of hydrogen. It comes from the water molecules contained in the comet. This shell is also increasing as it approaches the Sun.
As was mentioned at the beginning of the article comets carry a lot of useful information in his bowels, so scientists often refer to them as a time machine that can tell of the time of the birth of the universe. One way of obtaining such information is the analysis of comet tail with special radio telescopes, capable of determining the constituent substances, which some time ago were still part of the core. However, such an analysis gives only a General overview and astronomers have always wanted to look deeper into the comet and take of its substance. This project was carried out within the NASA project “Star Dust” – Stardust. A special missile was launched in 2005 to flying past Earth comet. The mission was the fact that the machine flew through the comet’s tail and collected a part of the substance, after which he returned to Earth in 2006. The results of this expedition contain a huge amount of information which is investigated till now.