Humans have been looking for the source, we try to understand the origin of life, to understand the structure of the earth and the formation of the solar system. Although the solar system looked very simple, as the astronomers tried to study the solar system, they encountered some difficult puzzles.
Why is the solar system what it is today? Why are the planets in the system coming to where they are today? Astronomers have used computers to construct many models to simulate the origin and evolution of the solar system, and many hypotheses have been put forward to answer these questions.
Core accretion theory
At present, astronomers agree that the sun and its planet were born in a nebula 4.6 billion years ago. The nebula consists of gas and dust. The dense gas and dust mass will gather the less dense matter from the surrounding area by gravity. Finally, the center of the nebula forms a sun because of the contraction. An opaque ring of gas and dust stretches around the sun and is called the “protoplanetary disk.”
As early as 1755, the German philosopher Immanuel Kant proposed the above ideas. Later theorists have been refining the details of the formation of the solar system and taking into account the distribution of the planets in the solar system. They first proposed some theories that explain the formation of planets, such as the core accretion theory, that is, after the formation of the sun, static electricity causes the particles in the protoplanetary disk to gather together to form a loose structure, which eventually grows to a few kilometers in diameter. The micro-satellite, then under the action of gravity, the micro-stars collide and combine, and the planets gradually form around the sun, and these planets orbit around the sun.
The core accretion theory holds that planets are formed where they are today, and the accretion process produces different results at different locations. Earth-like rocky planets (Mercury, Mars, Venus) are called terrestrial planets because they are less distant from the sun, and volatile water and methane molecules are difficult to aggregate. Therefore, rocky planets are mainly composed of metals such as iron and nickel. Made up of metal compounds, the volume of terrestrial planets is also relatively small. The huge gas planets are called wood-like planets (Jupiter, Saturn, Uranus, and Neptune), which are located farther from the sun, lower in temperature, and can be concentrated in large quantities of gas and ice.
However, this theory is difficult to explain the existence of Trojan asteroids (a large group of asteroids that share the same orbit with Jupiter) and the Kuiper Belt (outside the Neptune orbit). Therefore, astronomers now generally believe that the location of the planets is different from the current location, and they have undergone a series of evolutionary processes before they reach the present orbit.
To this end, astronomers use computers to simulate the evolution of celestial bodies, which can more or less explain the various phenomena in the solar system. Among them, the Nice model is the most widely accepted early evolution model of the solar system in recent years.
In the Nice model, the original orbits of the four wood-like planets are nearly circular and close to the sun, and they are also very compact. They are in a protoplanetary disk filled with small rocks and ice. When micro-planets interact with gas planets, micro-planets scatter into the solar system, and Saturn, Neptune, and Uranus move toward the edge of the solar system. Many micro-planets that scatter inward fall into the gravitational field of Jupiter and become Trojan asteroids. When Uranus and Neptune crossed the outer ice tray, some of the material was thrown inside, hitting the Earth-like planet, and other substances were thrown outwards to form the Kuiper Belt.
Although the Nice model fits perfectly into the look of today’s solar system, it does not explain the orbital problem of Mercury. Mercury is the closest planet to the Sun. Its orbit is elliptical. The orbit of Mercury is the narrowest of the orbits of all the planets in the solar system. When the orbits of other planets are almost in the same plane, the orbital plane of Mercury and other orbits. The plane in which it is formed has an angle of 7°. And the Nice model is very unstable. Uranus or Neptune will always be driven out of the solar system, leaving only three gas planets.
“Jumping Jupiter” hypothesis
Subsequently, David Nesworthy, a researcher at the Southwest Research Institute in Colorado, and Fernando Roig, a Brazilian planetary scientist, proposed “Jumping Jupiter” on the basis of the Nice model after repeatedly simulating and calculating planetary orbits. hypothesis. This hypothesis is a good explanation for the strange orbits of Mercury and the instability of the Nice model.
The two scientists said that in the original formation of the solar system, there is likely to be a huge gas planet, which is about the same size as Neptune, between Saturn and Uranus. During the outward migration of the gas planet, the planet was ejected out of the solar system. In the process, it also caused the Jupiter orbit to approach the sun, and the distance between Jupiter and the sun was rapidly shortened. Scientists describe the rapid migration of orbits as “Jupiter’s jump.”
This jump did not affect other rock masses of higher mass, only affecting the smallest mass of Mercury (the mass of Mercury is about one-twentieth of the Earth), causing the orbital displacement of Mercury. In addition, Jupiter Jump can also be used to explain the asteroid belt. Due to the gravitational influence of Jupiter, the micro-planets not only did not form planets, but collided with each other, forming many debris and debris. However, astronomers are unable to observe the traces of micro-planet collisions. If the solar system once had the fifth gas planet and the solar system expelled the planet again, this process would disrupt the orbit of the asteroid, so that it is difficult to observe the evidence of the collision, and everything is very reasonable.
If the initial solar system has only four giant gas planets, then the possibility of the solar system having today’s orbital layout will be very low. But if the original solar system originally had five gas planets, it would be much simpler to understand the formation of the solar system.