When modeling the individual stages of the protoplanetary cloud evolution and planet formation (Fig.), much attention is paid to the initial stage – the lowering of dust particles in the central plane of the disk and their clumping in the conditions of the pre-planetary cloud. The time of their lowering and the formation of a flattened dust disk depend on the speed of the growth of dust particles. The subsequent disintegration of the dust disk, the formation of dust clumps and their transformation into a swarm of compact asteroid-sized bodies with cosmogony. the point of view was quite fast ( 6 years). The next stage – the accumulation of planets from a swarm of “intermediate” bodies and their debris – took much longer. In the study of this stage, computer modeling is increasingly used. The results of the calculations clearly demonstrated the dependence of the finite number of planets on the mass of matter in the pre-planetary cloud. S. Dole (USA) found that with a cloud mass > 0.15.
10 8 years), previously estimated analytically. methods. The process of formation of the planets of the Earth group has already been traced in sufficient detail. The resulting method of numerical simulation of the distance between the planets, their masses, periods of their own. the rotations and tilts of the axes agree satisfactorily with the observations.
The process of formation of the giant planets was more complex, and many of its details have yet to be clarified. There are two hypotheses about the formation of Jupiter and Saturn, which contain a lot of hydrogen and helium (in their composition they are closer to the Sun than other planets). The first hypothesis (“contractions”) explains the” solar ” composition of the giant planets by the fact that in the protoplanetary disk of a large mass, massive gas-dust clumps-protoplanets – were formed, which then in the process of gravitation. they turned into giant planets. This hypothesis does not explain the removal from the Solar System of large surpluses of matter that did not enter the planets, as well as the reasons for the difference in the composition of Jupiter and Saturn from the sun (Saturn contains more heavy chemical elements than Jupiter, which, in turn, contains them relatively more than the Sun). According to the second hypothesis (“accretion”), the formation of Jupiter and Saturn took place in two stages. On the first one, which lasted approx.
10 8 years) most of the gas has already left the Solar System.
The small bodies of the Solar System-asteroids and comets-are the remnants of a swarm of “intermediate” bodies. Asteroids are rocky bodies in the interior. near-solar zone, comets – rocky-icy bodies of the zone of giant planets. The masses of the giant planets, even before the completion of their growth, became so large that their attraction began to greatly change the orbits of small bodies flying past them. As a result, some of them have acquired very elongated orbits, including orbits that go far beyond the planetary system. On bodies moving farther than 20-30 thousand au from the Sun, a noticeable gravitational field. the nearby stars were affected. In most cases, the impact of stars led to the fact that small bodies stopped entering the area of planetary orbits. The planetary system was surrounded by a swarm of rocky-icy bodies, extending to distances of 10 5 au. (
1 pc) and is the source of the currently observed comets. The existence of a comet cloud was established by the Dutch astronomer Ya. Oort (1950). The influence of nearby stars can sometimes disturb the orbit of a rocky-icy body so much that it will leave the Solar system altogether, and sometimes it can transfer it to an orbit passing in the vicinity of the Sun. Near the Sun, ice bodies begin to evaporate under the influence of its rays and become visible – there is a comet phenomenon.
Asteroids have survived to our time due to the fact that the vast majority of them move in a wide gap between the orbits of Mars and Jupiter. Similar rocky bodies that once existed in the entire zone of the planets of the Earth group have long since joined these planets, either collapsed in mutual collisions, or were thrown out of this zone due to gravity. the impact of the planets.
The largest of the sovr. asteroids-with a diameter of 100 km or more-were formed in the era of the formation of the planetary system, and the medium and small ones are mostly fragments of large asteroids that broke up during collisions. Due to the collisions of asteroid bodies, the supply of dust matter in interplanetary space is continuously replenished. Another source of small solid particles is the decay of comets during their passage near the Sun.
The bowels of the “primary” large asteroids were apparently heated to about 1000 o C, which affected the composition and structure of their matter. We know this due to the fact that small fragments of asteroid meteorites fall on the Earth’s surface, their composition and phys. sv-va k-ry indicate that they have passed the stages of heating and differentiation of the substance. The reasons for the warming up of asteroids are not completely clear. Perhaps the heating was due to the release of heat during the decay of short-lived radioactive isotopes; asteroids could also be heated by mutual collisions.
Some meteorites represent the best samples of “primary” planetary matter available to us. In comparison with terrestrial rocks, they are incomparably less changed by subsequent physical and chemical processes. The ages of meteorites, determined by the content of radioactive elements and their decay products, characterize at the same time the age of the entire Solar System. It turns out to be about 4.6 billion years old. Consequently, the duration of the process of formation of planets is insignificant in comparison with the time of their further existence.
The origin of systems of regular satellites of planets moving in the direction of the planet’s rotation in almost circular orbits lying in the plane of its equator, the authors of cosmogonic. hypotheses are usually explained by repeating on a small scale the same process that they propose to explain the formation of planets in the Solar System. Jupiter, Saturn, and Uranus have regular satellite systems, which also have rings of small solid particles. Neptune has no regular satellite system and apparently no rings. Sovr. planetary cosmogony explains the formation of regular satellites by the evolution of protosatellite disk-shaped swarms of particles that arose as a result of inelastic collisions near a given planet of planetesimals moving in near-solar orbits.
In the system of regular satellites of Jupiter, there is a division into two groups: silicate and water-silicate. Differences in chem. satellite observations show that the young Jupiter was hot (the heating could be due to the release of gravity). energy during gas accretion). In the system of Saturn’s moons, which consist mainly of ice, there is no division into two groups, which is due to the lower temperature in the vicinity of Saturn, at which water could condense.
The origin of the irregular moons of Jupiter, Saturn, and Neptune, i.e., moons that have a reverse motion, as well as a small number. the satellite of Neptune, which has a direct movement in an elongated orbit, is explained by capture.
The slowly rotating planets Mercury and Venus have no satellites. They apparently experienced tidal drag from the planet and eventually fell to its surface. The effect of tidal friction was also manifested in the Earth-Moon and Pluto-Charon systems, where the satellites, forming a binary system with the planet, are always turned to the planet by the same hemisphere.