What force "presses" the orbits of the planets so that they are almost on the same plane?
"I hope not to be convinced that something will have a good result, but to be certain that something is meaningful, regardless of the result."-Wenceslas Havel
Our solar system has eight inner and outer planets. These planets are of different sizes and are distributed in different orbits. Each one has its own unique nature and environment, but almost all of the planets' orbits are on the same plane. The entire solar system looks likeIt's like a flat disk with a raised center. But why?
The orbits of the major planets are basically in the agreed plane, which is almost perfect
At first glance, such perfect regularity seems very unlikely. Look at the picture below: this is the actual situation of our solar system.
Today, we can draw the orbits of the major planets with very high accuracy. We find that they all revolve around the sun on the same two-dimensional plane, and their orbital planes differ by up to 7 °.
In fact, if we take Mercury, the innermost and most orbiting planet out of the solar system, we will find that all other planets are aligned neatly: the deviation from the reference plane of the solar system or the planetAverage orbital plane is only about 2 degrees.
The plane of the planet's rotation orbit is also substantially perpendicular to the sun's rotation axis the sun itself is also rotating. Of course, the deviation of the sun's rotation axis from all planetary orbits is also within 7 °.
Such a regular order is contrary to our intuition. It makes people think that unless there is something that causes these planets to be trapped in the same plane. Because we think that the direction of the orbit can be completely random, and gravity to keep the planet stableThe force of the orbit is the same in all three dimensions.
So we may think that the solar system is more like a group of bees than a set of beautiful, orderly and nearly perfect circles. In fact, it is not wrong to think so. If we stay away from the solar system, outside the planets and asteroids,Out of the orbit of Comet Halley, outside the Kuiper Belt, and even outside the Oort Cloud, we will see a messy solar system. See picture below
So, what exactly caused our planet to form a disk? Orbiting the sun in a plane, not as a group?
To understand this, let's go back to the original formation of the solar system: starting with a cloud of gas molecules, it was exactly that that produced all the new stars in the universe.
When the mass of a molecular cloud is large enough, bound by gravity, and the temperature is low enough, it will shrink under the effect of its own gravity, just like the pipe Nebula in the upper left, it will form regions with sufficient density.Areas will generate new star clusters points in the upper right circle.
We will notice that this nebula and any similar nebula are not perfect spheres, but show irregular, slender shapes. Gravity is very discerning and can not tolerate any flaws, as long as there are slight unevennessIt will collapse, and gravity is a force that is inversely squared with distance. When the distance from a large mass object is halved, the gravity will increase four times, and the small difference in the initial shape of the gas cloud will be short.Greatly magnifies the gravitational force in one direction in time.
As a result, an extremely asymmetrically shaped star-forming nebula is formed. The place where the stars form is exactly where the gas density is the greatest. The problem is that when we look at the individual stars inside, they are perfect spheres, just like ourLike the sun.
But just when the nebula itself became very asymmetric, the individual stars formed inside the nebula came from imperfect, dense, asymmetric clumps inside the nebula.
The clumps first collapse in one of the three dimensions, because normal matter atoms consisting of nuclei and electrons collide with each other, and electromagnetic interactions occur, and they stick together.Eventually, a flat disk, or material disk, will be formed. At the same time, gravity will pull most of the material toward the center, where the stars form, but around it, we will see the so-called protoplanetary disk. HaThese disks have been directly observed by the Bo Space Telescope! It directly proves that our theory of planet formation is correct.
So from the beginning we got a protostellar galaxy that is more neat in the plane, rather than a randomly gathered sphere. To enter the next step, forming a planet, we must wait for theoretical modeling and simulation, because in a youngIn the stellar galaxies, the formation of planets takes at least a million years, and we can't observe them for a long time.
After the protoplanetary disk undergoes "collapse" in one dimension, it will continue to shrink as more and more materials are attracted to the center. But when most of the material is collected into the interior, a large amount of material will be here.Steady rotation in the disc.
This process has a physical quantity that must be conserved: angular momentum, which can tell us how the entire system gas, dust, stars rotates in essence. This means that all matter in the entire disc needs to be roughly along the sameClockwise or counterclockwise. Over time, the disc reaches a stable size and thickness, and then small gravitational instabilities will begin to create planets in the disc.
Of course, there are slight differences between the different parts of the planetary disk and the gravitational effects of interacting planets, and there are also slight differences in the initial conditions. The star formed in the center is not a single point,It's an object that stretches about a million kilometers. When you put all these factors together, it will cause all planets not to be in a completely standard plane, but will be very close.
In fact, it was not until 2015 that scientists discovered the first planetary system beyond our own, and we discovered the process of forming new planets on a protoplanetary disk.
The young star in the upper left of the above picture is located on the periphery of a nebula region, about 450 light years away, and is surrounded by a protoplanetary disk. This star itself is only about 1 million years old. ALMA-"Atacama"Millimeter / sub-millimeter wave array telescope" measured this protoplanetary disk at the millimeter waveband and returned us the image below.
It is obviously a disk, all matter is on the same plane, but there are black "slits" inside the disk. These gaps correspond to a young planet, which attracts all nearby matter! We do n’tKnowing which planets will merge together, which one will be kicked out, which one will migrate inward and be swallowed up by their parent star, but we are witnessing key steps in the development of a young solar system.
Summary: So why are all the planets on the same plane?
Because they are formed by asymmetric gas clouds, the gas clouds first collapse in the shortest direction, and all the materials "snap" into a disk, and then the materials shrink inward, but eventually around the centerAs the planets rotate, tiny density defects form in the young material disk, so they end up orbiting in the same plane, with a difference of at most a few degrees between each other.
This is another extraordinary universe story. Through theoretical simulations and the current observation of the universe itself, this story once again shows that there is an amazing consistency between our best scientific theory and the actual situation of the universe!
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