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The solar system.
The origin and development of the planetary system.
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Astronomers of the past proposed many theories of the formation of the Solar system, and in the forties of the twentieth century, the Soviet astronomer Otto Schmidt suggested that the Sun, rotating around the center of the Galaxy, captured a cloud of dust.
From the substance of this huge cold dust cloud, cold dense pre – planetary bodies planetesimals were formed.
Our Solar System is not the only one in the universe Elements of this theory are used in modern cosmogony.
According to computer calculations, the initial mass of the gas dust cloud in which the Solar System was formed was more than 104 M .
The initial size of the cloud was significantly larger than the size of the Solar system, and its composition was similar to that observed in dense cold interstellar nebulae, that is, 99 % of interstellar gas and 1 % of interstellar dust.
Several dozen stars have now been discovered to have planetary systems.
The telescope named after.
The young star HR 4796 was studied in the Hawaiian Islands by Keka.
In the obtained images in the infrared range, a disk with a radius of about 200 AU is visible around it.
The central part of the disk is free of dust.
It is believed that large planetary bodies have already formed from dust in the central region, and comets continue to form in the outer part.
Currently, the theory of the formation of a planetary system in four stages is generally recognized.
A planetary system is formed from the same protostellar dust matter as a star, and at the same time.
The initial compression of a protostellar dust cloud occurs when it loses stability.
The central part contracts independently and turns into a protostar.
Another part of the cloud with a mass about ten times less than the central part continues to slowly rotate around the central thickening, and at the periphery each fragment is compressed independently.
Another part of the cloud with a mass about ten times less than the central part continues to slowly rotate around the central thickening, and at the periphery each fragment is compressed independently.
At the same time, the initial turbulence, the chaotic movement of particles subsides.
The gas condenses into a solid, bypassing the liquid phase.
Larger solid dust grains particles are formed.
The larger the grains formed, the faster they fall on the central part of the dust cloud.
The part of the substance that has an excess torque forms a thin gas dust layer – a gas dust disk.
A protoplanetary cloud – a dust subdisc is forming around the protostar.
The protoplanetary cloud is becoming more and more flat, it is strongly compacted.
Due to gravitational instability, separate small cold clumps are formed in the dust subdisc, which, colliding with each other, form increasingly massive bodies planetesimals.
During the formation of the planetary system, some of the planetesimals were destroyed as a result of collisions, and some merged.
A swarm of pre planetary bodies with a size of about 1 km is formed, the number of such bodies is very large – billions.
Then the pre planetary bodies are combined into planets.
The accumulation of planets lasts for millions of years, which is very insignificant compared to the lifetime of a star.
The proto sun is getting hot.
Its radiation heats the inner region of the protoplanetary cloud to 400 K, forming an evaporation zone.
Under the influence of the solar wind and light pressure, light chemical elements (hydrogen and helium) are pushed away from the vicinity of the young star.
In a distant region, at a distance of more than 5 AU, a freezing zone is formed with a temperature of about 50 K.
This leads to differences in the chemical composition of future planets.
The evolution of the solar system.
As soon as the mass of the pro planet reaches 1-2 Earth masses, it is able to capture the atmosphere.
Proto Jupiter has literally increased its mass tenfold over a hundred years due to the capture of gases.
Then the accretion rate decreases, because all the gas directly in the path of the planet has already been absorbed, and from the outside it comes quite slowly (due to diffusion).
In our Solar System, giant planets have formed on the periphery, capable of holding gas shells near them.
First, the cores of the giant planets were formed, and then the planets "built up" a shell of hydrogen and helium.
The two stage model of giant formation is confirmed by the facts.
The masses of the cores of the giant planets are approximately the same and equal to 15-20 M .
The amount of hydrogen decreases with increasing distance.
The greater the mass of the planet, the faster the accretion of gas on it goes.
According to modern calculations, the growth of Jupiter lasted for tens of millions of years, and the growth of Saturn – hundreds of millions.
The giant planets had their own minidisks of gas and dust, from which rings and numerous satellites were then formed.
During the formation of Jupiter, it was in the area of its orbit that the boundary of condensation of water vapor passed.
According to modern calculations, at closer distances, in the asteroid belt, volatile substances were in a gaseous state.
This led to the fact that the growth of pre planetary bodies in the area of the future Jupiter accelerated, and slowed down in the area of the asteroid belt.
That is why the massive Jupiter has overtaken the protoplanet closer to the Sun in terms of growth rate.
But after its" birth", Jupiter began to slow down the formation of this planet in the asteroid belt.
The clumps of matter dispersed by the gravity of the giant planets were thrown out to the outskirts of the Solar System, where they became comets.
Gravitational disturbances from Jupiter are still strongly affecting asteroids.
Uranus and Neptune grew even more slowly.
By that time, there was even less gas left in the Solar System due to the action of the solar wind, so Uranus and Neptune contain less hydrogen in percentage than Jupiter.
The main components of these giant planets are water, methane and ammonia.
Less massive planets have formed in the center of the Solar system.
Here, the solar wind blew out small particles and gas.
But the heavier particles, on the contrary, tended to the center.
The growth of the Earth continued for hundreds of millions of years.
Its bowels warmed up to 1000-2000 K due to gravitational compression and large bodies involved in the accumulation (up to hundreds of kilometers across).
The fall of such bodies was accompanied by the formation of craters with pockets of elevated temperature under them.
Another and the main source of the Earth's heat is the decay of radioactive elements, mainly uranium, thorium and potassium.
Currently, the temperature in the center of the Earth reaches 5000 K, which is much higher than at the end of accumulation.
The solar tides slowed down the rotation of the planets close to the Sun Mercury and Venus.
With the advent of radiological methods, the age of the Earth, the Moon and the Solar System was precisely determined – about 4.6 billion years.
Computer experiments have demonstrated a remarkable property of our planetary system: the passage of a star with a mass of about 0.1 of the mass of the Sun through its outer regions will not change the orbits of the planets of the Earth group much.
The same cannot be said about remote objects located in the Oort Cloud, for which the distance from the Sun is hundreds of times greater than the radius of the Earth's orbit.
The gravitational field of the Galaxy perturbs the orbits of small bodies on the outskirts of the Solar system and even causes their appearance inside the Earth's orbit.
As for the Sun, the central body of the Solar system, it is a typical main sequence star, the equilibrium of which is due to the equality of the forces of gas pressure and gravity.
The sun has existed for 5 billion years and will emit an almost unchanged flow of energy for the same amount of time due to nuclear reactions occurring in its bowels.
Then, in accordance with the laws of stellar evolution, the Sun will turn into a red giant, and its radius will increase significantly, it will become larger than the Earth's orbit.
After that, the gas shell will dissipate, and a white dwarf will remain in the place of the Sun.
This remnant of our former luminary will highlight the reserves of thermal energy for billions of years, gradually turning into an invisible cold object.
At the same time, the temperature on Earth will first increase to 10,000°C, and then decrease to almost absolute zero.
Modern planetary cosmogony meets with many issues that require a strict solution.
One of such questions is the paradox of the rotational moment.
Protoplanetary disks have a small mass, 10-100 times smaller than the central star.
For example, in the Solar system, 99.8 % of the mass consists of the Sun.
Nevertheless, the main rotational moment falls on the planets.
Therefore, the question of the redistribution of the rotational moment from the central part of the condensing gas dust cloud to the periphery is very relevant and has not yet been resolved.
Astronomers of ancient times believed that the universe and the Solar system existed forever and will exist for as long as in an unchanged form.
With the advent of Christianity, the age of the Solar system has significantly decreased.
Giordano Bruno was the first to suggest that stars, like the Sun, are surrounded by planetary systems that are constantly being born and dying.
In 1745, the French scientist Buffon hypothesized that the planets were formed from matter ejected from the Sun after the collision of the Sun with a comet.
The German philosopher Immanuel Kant in 1755 first outlined the idea of the emergence of the Solar system from a cloud of cold dust particles in chaotic motion.
According to Kant, planets are formed from the same gas dust cloud as the Sun.
In 1796, the French scientist Pierre Simon Laplace described the formation of the Sun and the Solar system from a slowly rotating incandescent gas nebula.
Under the influence of gravity, the central part of the protosun was compressed, the speed of its rotation increased, so it acquired a flattened shape.
The clots were separated from the protosun and then cooled.
The substance from which the planets were formed, initially according to Laplace, was in a hot, molten state.
But then it became clear that the Earth had never been either gas or hot.
Jeans ' hypothesis of the formation of planets in the Solar system.
A new theory proposed in 1916 by James Jeans, according to which a star passed near the Sun and its attraction caused the release of solar matter, from which planets were subsequently formed, was supposed to explain the paradox of the distribution of the angular momentum.
However, at present, experts do not support this theory.
In 1935, Russell suggested that the Sun was a double star.
The second star was torn apart by the forces of gravity during a close approach with another, third star.
Nine years later, Hoyle proposed the theory that the Sun was a double star, and the second star went through the entire path of evolution and exploded as a supernova, throwing off the entire shell.
From the remnants of this shell, the planetary system was formed.
In the forties of the twentieth century, the Soviet astronomer Otto Schmidt suggested that the Sun captured a cloud of dust while orbiting the Galaxy.
From the substance of this huge cold dust cloud, cold dense pre – planetary bodies planetesimals were formed.
Elements of many of the theories listed above are used by modern cosmogony.
Source of information: "Open Astronomy 2.5", LLC "FIZIKON" Main page of the section
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