Comet's Structure

The comet does not have a fixed volume, it is away from the sun, a small volume; close to the sun, coma becomes larger and larger, the tail becomes longer, the volume becomes enormous. Tail longest actually up to more than 200 million kilometers. The comet quality is very small, The average density of the nucleus of one gram per cubic centimeter. Coma and tail of the material is extremely thin, its quality accounted for only 1% to 5% of the quality, or even smaller. The comet substance is mainly composed of water, ammonia, methane, cyanide, nitrogen, carbon dioxide, etc., the nucleus by condensing into ice water, and carbon dioxide (dry ice), ammonia and dust particles mixed composition "dirty snowball"! General comet is composed by two parts of the comet head and tail. The comet head including the two parts of the comet nucleus and coma. From 1920 sounding rockets, satellites and spacecraft after detection of the comet at close range, and surrounded by a giant cloud of some comets out of coma by a layer of hydrogen atoms, known as the "coma cloud" or "hydrogen cloud". So we can say that the comet head to the actual composition of the nucleus, coma and coma cloud. The comet nucleus is the the comet most central, most essential, the most important part. Generally considered to be solid, and is composed of stones, iron, dust and ammonia, methane, and ice. The small diameter of the comet nucleus, a few kilometers to a dozen kilometers, only a few hundred meters. Coma: the nucleus of gas and dust around the planet like mist. Radius of up to hundreds of thousands of kilometers, the average density of less than a billionth of a billionth of one of the Earth's atmospheric density (about 1 g / cc). Through spectral and radio observations, the coma gas main ingredient is neutral molecules and atoms, including hydrogen, hydroxy, oxygen, sulfur, carbon, carbon monoxide, an amino, cyano, is satisfied, etc., and also found that a relatively complex cyanide hydrogen (HCN) and methyl cyanide (CH3CN) compound. These gases flowing outward from the center to an average of 1-3 km / sec velocity. Coma cloud: cloud by hydrogen atoms in the coma, it is also known as the hydrogen cloud. Up to 100 million to 10 million kilometers in diameter, but some comet coma cloud. According to the characteristics of the shape and composition of the comet head, can be divided into the "no-fat comet head, bulbs shaped comet head, anchor-shaped coma head and so on. The tail of the comet close to the sun about 300 million kilometers (2 astronomical units) began to appear, gradually from small to great changes long. When the comet perihelion (comets come from the sun that) away from the sun, the tail gradually smaller until no. The general direction of the tail always carrying the extension of the sun, when the comet close to the sun, the comet tail trailing behind, when the comet from the sun to flee, the tail has become a leading. Tail of the large volume, but the material is very thin.Tail length, width, the general tail length of between 10 million to 150 million one thousand meters, and some much longer surprising, across half the sky, such as the 1842 Ⅰ comet's tail as long as 320 million kilometers, extending from the sun to the orbit of Mars. General tail width between 6000-8000 km, most of the 24 million meters wide, the narrowest of only 2,000 kilometers. The size of the repulsion according to the shape of the tail of the sun, the tail is divided into two major categories. A class for "ion tail" by the plasma gas composition, such as carbon monoxide, hydrogen, carbon dioxide, carbon, hydrogen group, and other ionizable molecule. Such relatively straight, thin and long tail, so-called "gas tail or tail type I Other for the dust tail is composed of dust, yellow dust repulsion the sun photon radiation pressure to form. The tail is bent, bending larger, wide, referred to as II-type impeller; maximum bending process, and the short, wide, referred to as III-type impeller.In addition, there is something called the "abnormal tail, the tail extends toward the solar system, the direction of the fan-or spike-like. Usually a comet tail of the two or more different types.