The structure of comets
Unlike planets, comets move on highly elongated orbits, and therefore are visible only at short periods close to the Sun.
The main part of any comet is its nucleus .
According to the hypothesis of the famous American researcher of comets Fred Lawrence Whipple, cometary nucleus is an ice consisting of a mixture of frozen water and frozen gases interspersed with refractory rocky and metallic particles . Figuratively speaking, it looks like a “dirty iceberg”.
Let us imagine that we see the newly opened the comet, which is somewhere in the vicinity of Jupiter’s orbit. Seeing through the telescope hazy pale speck, like a spherical nebula (such unattractive are presented to the observer of a distant comet), we may be disappointed at first. With the approach of the comet to the Sun the solar flux increases. Comet “ice” begin to evaporate rapidly. Around the nucleus formed a vast glowing gas shell – coma. Together with the core of it is the head of the comet.
Comets (from the Greek kometes, long — haired), the bodies of the Solar system, moving on highly elongated orbits far from the Sun appear as faintly glowing specks oval, and approaching the Sun they have a “head” and “tail”. The Central part of the head is called the nucleus. Diametrer 0,5-20 km, a mass of 10 11 -10 19 kg, the core is ledenite body — a conglomerate of frozen gases and dust particles. The tail of a comet consists of a release from the nucleus under the influence of sunlight molecules (ions) gases and dust particles, tail length can reach tens of million km the Most famous periodic comet is Halley (period P=76 years), ENKA ( P=3.3 years), Schwassmann — Wachmann (comet’s orbit lies between the orbits of Jupiter and Saturn).
Further approach of the comet with the Sun leads to the fact that her head is oval, then elongates and develops from her tail . Because of tails, reminiscent at times of flowing hair, these celestial bodies were called comets. Comet tails are generally directed in the direction opposite the Sun. The latter circumstance indicates the existence of a special power that emanates from a radiant Shine and repelling comet substance. In the beginning of XX century after the experiments of the eminent Russian physicist P. N. Lebedev (1866-1912), it became clear that this pressure of sunlight on molecules of gases and dust particles released from the comet nucleus.
It is estimated that the distance from the Sun equal to the average radius of earth’s orbit (1 and. E.), the dust particle size to 1/5 micron will be in equilibrium, i.e. the force of attraction of such dust to the Sun will be balanced by the pressure of light rays. And for particles smaller radiation pressure prevails over the force of gravity, and they will be removed from the Sun.
As an exception, meet the comet, in addition to having a tail directed away from the Sun, one straight tail, facing to the sun. Such an unusual tail observed in 1835 by the German astronomer Friedrich Bessel (1784-1846) in comet Halley. But the most expressive of the anomalous tail was, the comet Kohoutek . Him 29 December 1973, drew the attention of American astronauts making the flight on the orbital station “Skylab”.
The appearance of the anomalous tails is associated with the emission from cometary nuclei large dust particles – ranging in size from 0.1 mm and larger. The main effect on these particles has already not radiation pressure and the gravitational force. Rushing under its influence to the Sun, they form a comet of unusual, abnormal tail.
Scientists estimate that the mass of cometary nuclei can be from a few tons from micro to billion comets and perhaps many trillion tons of comet giants. But the shorter the period of the comet and therefore the more the comet goes around the Sun, the faster melts and “losing weight” its core. Fred L. Whipple calculated that in one passage near the Sun the comet can lose by evaporation hundreds of millions of tons of volatiles and dust.
In 1908 he observed the comet of Morgause. In its tail were found particles of a substance moving with very great acceleration. The calculations showed that they are repulsive forces, a thousand times the force of gravity of the Sun.
To explain this one-the pressure of light was impossible. I had to look for another cause. And such a reason was found: the culprit turned out to be the solar wind – streams of plasma continuously ejected from the solar corona into interplanetary space. This opened the wind was in our time with the help of spacecraft, but the first witnessed his comets.
The rapid flow of solar corpuscles of matter is in danger of gases and vapours in the head of the comet, ionize them creating a plasma and carry the cometary plasma at high speeds away from the Sun. And the stronger the wind blows, the straighter and longer the comet tail. But if the dust tail shines reflected sunlight, plasma fluoresce, emits its own rays from the ultraviolet radiation of the Central star.
To check the cometary hypotheses, particularly hypotheses about the ice core, in Leningrad physico-technical Institute named after academician A. F. Ioffe, experiments were conducted with artificial cometary nuclei. Interesting results on the modeling of cometary phenomena have been obtained by physicists Eugene A. Kaimakov and Viktor Ivanovich Surkovym. In the vacuum chamber, where they are to create conditions similar to the conditions of outer space, they studied the behavior of artificial cometary nuclei. As “cores” was used pure and dusty ice of different chemical composition. It turned out that upon irradiation of the nucleus of such intense light like the sun, its surface can form a matrix, dust or crust. It has high thermal insulation properties, which prevents the penetration of solar heat into the interior of the nucleus and sublimation of cometary matter – the transformation of ice to vapor, bypassing the liquid state.