How are planets formed? Some say it was arranged by advanced civilizations. Is this true?

This article is based on answering questions from netizens, see the screenshot below:

To put it bluntly, I don't think so.

Because modern astrophysics has a clear understanding of the laws of the birth of the universe and the birth of planets. This law is "force". It is the effect of the four basic forces discovered in the universe so far that make the universe what it is.

The four fundamental forces are gravitational interaction, electromagnetic interaction, strong interaction, and weak interaction. There have been many explanations of these four forces in the past, so I won’t go into detail today.

Planets are the most common and most common entities in the universe. They can be understood as individual celestial bodies in the universe that are spherical, including stars and planets. There are not many spherical planets in the solar system. Only the sun, the eight planets, a dozen dwarf planets, some satellites of large planets, and some asteroids are spherical in appearance.

The planet becomes a sphere mainly due to gravity.

Universal gravitation was discovered by Isaac Newton, a pioneer of modern science. It is the first of the four fundamental forces discovered by humans. Since then, human understanding of the universe has entered the modern scientific era. The core of universal gravitation is that as long as objects have mass, no matter how big or small, they will attract each other. The magnitude of gravity follows the law that is proportional to the mass and inversely proportional to the square of the distance.

The law of universal gravitation is expressed as: F=GMm/r^2. Here F represents the gravitational value, in units of N (Newton, N=kg*m/s^2); G is the gravitational constant, that is, the gravitational force when two 1 kg objects are 1 meter apart, with an approximate value of 6.67*10^-11N·m^2/kg^2; M and m are the magnitude of the gravitational interaction and the mass of the two objects, in units of kg (kilograms); r is the distance between the centers of mass of the two gravitationally interacting objects.

Under the action of gravity, fluids such as gas and liquid will approximate a sphere as long as they condense; and rocky solid planets can easily form a sphere in the lava fluid state in the early stages of their formation; but after cooling, the formation of a sphere is related to mass and volume, and the greater the mass and volume, the greater the possibility of forming a sphere.

This is because any macroscopic matter has two forces in conflict. One is the electromagnetic force, which is manifested as the molecular bond energy in solid matter and requires the matter to maintain its original state; while the gravitational force is manifested as gravity on the planet, which requires all matter to be pulled toward its center of mass. The result of the balance is to pull all the surface matter to the same distance from the center of mass, so that the planet becomes spherical.

The planet becomes spherical because gravity has the upper hand after the two forces compete with each other. How big is this "upper hand"? It is through the action of gravity that the material form that is sufficient to destroy the material retained by the electromagnetic force inside the material is formed. (See the figure below)

In order for the protrusion to generate sufficient force to collapse spontaneously, the following condition must be met: 4/3πGρrh＞E0/μ.

Here ρ represents the average density of rocky planets, r is the radius of the planet, h is the height of the protrusion on the surface of the planet, μ is the molecular molar mass, and E0 is the bond energy per mole of molecule.

From this we can see that the height of the protrusions on the surface of a planet is restricted by density (mass) and volume (distance from the center of mass). Under given density conditions, the larger the volume of a planet, the more likely it is to be spherical. For example, the density of the Earth is 5.5*10^3 kg/m^3. For a planet with a similar density to the Earth, in order to keep the protrusions on the surface no higher than 0.01r, the radius of the planet must be at least 2300km (kilometers or kilometers).

As the mass and volume of a planet continue to increase, the height ratio of the surface protrusions will become smaller and smaller, and as the mass and volume of a planet continue to decrease, the height ratio of its surface protrusions will become larger and larger. According to calculations, when the volume radius of a planet with the same density as the Earth is less than 700km, its surface protrusions can reach 0.1r. The smaller the protrusion, the higher the protrusion. That is, the peak of a planet with a radius of 700km can reach 70km, and the peak of a planet with a radius of 500km can reach 100km.

In this way, the planet cannot be spherical. Of course, this is the condition for a planet with a density about the density of the earth to be called spherical. If the density is very small or the surface is a fluid, the volume of the spherical body can be even smaller. Scientists describe the condition for a celestial body to be spherical as: the mass is sufficient to overcome the solid gravity to achieve hydrostatic equilibrium.

How many spherical planets are there in the solar system?

In the solar system, there are about 40 planets with a volume radius greater than 700 kilometers. They are:

The star Sun has a radius of 69.6km and a mass of 1.989*10^30kg, accounting for 99.86% of the mass of the entire solar system; the eight planets, from near to far from the Sun, are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. I won’t go into details about their volume, radius, and mass. If you are interested, you can search for relevant information.

There are 7 confirmed dwarf planets and candidates, including Pluto, Charon, Eris, Ceres, Makemake, Haumea and Gonggong. Among them, Charon, Ceres and Haumea have a radius less than 700km, so they are not very spherical. Haumea is an olive shape (pictured above).

There are 11 satellites with a radius greater than 700km, from largest to smallest: Ganymede, Titan, Callisto, Io, the Moon, Europa, Triton, Titania, Rhea, Titania, and Iapetus. The largest one, Ganymede, has a radius of 2631km, and the smallest one, Iapetus, has a radius of 735km.

Of course, some icy bodies are very small, with a diameter of only about 150 km, and are also spherical in shape. This is because the surface of these planets is composed of ice formed by fluids such as water and methane. There are 9 such satellites.

There are also some icy celestial bodies that have been discovered, some of which are also close to spherical. Because they are still being discovered and observed, they will not be introduced one by one.

The process of planet formation

The planets in the universe are mainly concentrated in the planetary system. A planetary system refers to a celestial system centered on a star, including planets, satellites, dwarf planets, asteroids, comets and interstellar dust, etc. These celestial bodies all move around the main star under the gravitational force of the main star, such as the solar system.

In fact, all celestial bodies below the planets are subsidiary structures of stars. They are formed by the condensation of some small particles in the planetary disk during the formation of stars. The force that condenses these small particles is gravity.

The parent body of a star is a nebula, also called a molecular cloud or interstellar dust. It is mainly composed of the lightest elements in the universe, hydrogen and helium, and contains about 1% of elements heavier than hydrogen and helium. The proportions are different from the source of this molecular cloud. The earliest molecular cloud formed in the early days of the Big Bang contained only a small amount of lithium and no other heavy elements, except hydrogen and helium. It was due to stellar nuclear fusion and supernova explosions that more and more heavy elements were produced.

Our solar system was formed from a nebula after a supernova explosion, and it is very likely that the nebula was formed after several explosions. Because of this, the composition of the sun is only about 1% heavy elements, and the proportion of heavy elements on the earth where we live is even greater.

Although the gravitational force between nebula particles is extremely small, they will still slowly attract each other and come together. If they encounter disturbances such as gravitational waves from supernova explosions, this condensation will accelerate. As they gather more and more tightly, they will gradually become a ball, and the gravitational force between them will become stronger and stronger.

Due to the unbalanced contraction, the nebula will gradually rotate, and the centrifugal force of the rotation will form a nebula disk, or dust disk, on the equatorial plane. This nebula disk is called a planetary disk, and the future planets and all the small celestial bodies in this system are formed and run in this disk.

Under the influence of gravity, the nebula in the core shrinks faster and faster, and finally forms a collapse state. The huge pressure and temperature in the core strip the extranuclear electrons of hydrogen atoms, and violent collisions and fusions occur between nuclei, thus nuclear fusion occurs. The huge radiation pressure of nuclear fusion offsets the pressure of the nebula contracting inward, gradually achieving a balance, and continuously releasing radiation energy to the outside, a star is born, and enters the main sequence stage.

The basic condition for the birth of a star is that the mass of the gathered nebula must be at least 0.07 times the mass of the sun. Only in this way can the core pressure and temperature be sufficient to activate sustained nuclear fusion. The smaller the mass of a star, the lower the core pressure and temperature, the gentler the nuclear fusion reaction, the less fuel consumption, and the longer the lifespan; conversely, the larger the mass, the greater the core pressure and the higher the temperature, the more intense the nuclear fusion reaction, the faster the fuel consumption, and the shorter the lifespan.

The smallest mass stars are called red dwarfs, and the longest lifespans can reach trillions of years. The most massive stars discovered now have masses more than 200 times that of the sun, such as R136a1, and their lifespans are only about 3 million years.

This is how the solar system was formed. The sun is a medium-to-small mass star, called a yellow dwarf, with a lifespan of about 10 billion years. During the formation of the sun, 99.86% of the mass of the entire system was absorbed. At the same time, small particles and rocks in the planetary disk collided and attracted each other, gradually condensed together, and like a snowball, it rolled bigger and bigger, and gradually formed planets.

A planet will eat up all the debris and objects in its orbit and occupy a single orbit. As objects of all sizes form, the planetary disk will become more and more empty.

Under the influence of the sun's gravity, these planets and celestial bodies almost all revolve around the sun in this planetary disk, which is called the ecliptic. During the formation process, each planet was hit by various impacts, so its rotation axis tilted, and the tilt angle was different.

Many small celestial bodies are attracted by the gravity of planets and move around them, which are called satellites. For example, the moon is the only satellite of the earth, Mercury and Venus have no satellites, Mars has 2, and Jupiter, Saturn, Uranus, and Neptune all have many satellites, with a total of more than 200 satellites of all sizes.

There are tens of thousands of galaxies in the universe, and countless stars and planets. Since stars also have a lifespan, these planets are constantly born and die. Therefore, the formation of planets is not arranged by advanced civilizations, but a manifestation of natural laws. The greatest force that influences the formation of planets is gravity.

What do you think of this explanation? Welcome to discuss, thank you for reading.

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