Comets of the Solar system
Comets: the oldest inhabitants of the Solar system
J. L. Lagrange (1813) was also based on firmly established facts – the presence of comets that definitely move in elliptical orbits, including short-period. He explained the origin of comets gigantic volcanic explosions – emissions (eruption) with giant planets. It is, in principle, could explain the nature of the orbits of short-period comets. Subsequently, the views of La Grange shared and developed a number of scientists, among which the most important contribution of the Soviet astronomer S. K. Bo, who worked in this direction with the 20-ies to 80-ies of our century. He has eliminated the biggest internal difficulty is the concept of Lagrange – the necessity of the ejection of cometary masses (nuclei) with the “surface” of the giant planets with their powerful gravity fields, the overcoming of which requires an initial speed of 60 km/s and more. Giant planets also have thick (the length of many thousands of miles) and very dense atmosphere, in the middle of the twentieth century has been very problematic the very existence of a solid surface planets – giants beneath these atmospheres. All saints “moved” the eruptive source of emissions of cometary bodies with the giant planets on their major satellites. Of course, the important contribution of all saints in the cometary cosmogony was the opening of a prominent “secular” (in astronomy, the term refers to a change that is proportional to the time, in this case systematic, from turnover to turnover) reduce the brilliance of many short-period comets. It’s definitely meant “youth” of these comets, in the sense of their recent arrival to the inner Solar system.
In 1950, based on the study of several characteristic sverhdorogimi comets, the Dutch astronomer Jan Oort proposed the hypothesis (in less developed form, it was also expressed earlier by E. Opik and G. V. fesenkova a) the existence of the far, “predvestniki” the periphery of the Solar system, at distances from the Sun up to 100 – 150 thousand. E. giant, almost spherical cloud of cometary bodies (cometary nuclei), containing about 100 billion of these objects. They, however, belong (in the sense that they do not leave) the Solar system. Originally Oort believed that cometary bodies were thrown to the far periphery of the Solar system in the explosion of one of the planets of the Solar system. But in the next (1951) year he published a work, where in fact moved on this issue (or may have independently developed similar views) on positions developing actively then cosmogonic theories of Schmidt and his school. According to this concept, cometary bodies were formed in the gas-dust protoplanetary disk, in the same, in which was formed the whole Solar system planetesimals its outer (cold) zone. At the same time formed and the giant planets, their masses growing by accretion of planetesimals, gravitational perturbations from them was increasing and the planetesimals, which were not part of the planets that were ejected from the Solar system. Basically they with hyperbolic speeds is gone forever in the Galaxy, but a small part of them (according to V. S. Safronov, on the order of 1% – 2%), thanks to the stellar gravitational perturbations has been translated into not too elongated orbits with large semi-axes and atelinae distance (the greatest distance from the Sun) about 100 thousand. E. (Distance to the nearest stars from the Sun are some more than 200 thousand. E.).
The vast majority of comets orbit the Sun in elongated elliptical orbits. Classification of comets is made, primarily, by period of their circulation. So, comets with periods less than 200 years are called short-period, with periods over 200 years – long-period. Now there are about 700 long-period comets. These will include and a special group of “scratching” the Sun of comets that are at perihelion close to the Sun. Such comets there are about 30. Approximately 15% of all long-period comets are “new” (also known as parabolic) – these comets approach the Sun for the first time from the peripheral areas of the Solar system. Other long-period comets (the”old”) held through the Central region of the Solar system. The inclinations of the orbits of long-period comets to the plane of the Ecliptic are distributed randomly.
The inclinations of the orbits of short-period comets (there are over 200 known) to the Ecliptic plane, as a rule, small. It is assumed that short-period comets is the result of a long evolution of long-period comets in the gravitational field of large planets and the Solar system, primarily Jupiter. Short-period comets are divided into families according to their Aveling distance. Comets with afaliny distance, close to the semimajor axis of Jupiter’s orbit (5.2 a.e.) called comets of the Jupiter family. Their periods of revolution around the Sun do not exceed 20 years. Such comets there are about 150. The family of comets from other planets in the Solar system: Saturn, Uranus and Neptune are much smaller. To the family of Neptune belongs, in particular, Halley’s comet and comets of Olbers and Pons-Brooks, and some others. The prevalence in the population of comets of the Jupiter family due to the fact that gravitational perturbations from Jupiter statistically 10 times stronger than Saturn’s, and 100 times stronger than any other planet.
Strong gravitational perturbations from major planets, as well as the expiration gas jets from the nuclei of comets when they approach the Sun, lead to strong changes in the orbital elements of comets. Therefore, conventionally, we can talk about their “chaotic” motion in space of the Solar system