Where is the boundary of the solar system? Kuiper belt? Oort cloud? The solar system has been expanding

As we all know, in the solar system, the sun is the absolute center, and all other celestial bodies revolve around the sun. But do you know where the boundary of the solar system is?


At first, it was thought that the boundary of the solar system was Saturn, which is about 1.4 billion kilometers away from the sun. But this conclusion was changed by the discovery of Uranus, the seventh planet of the solar system, by British astronomer Herschel in 1781. That year, the boundary of the solar system was extended to about 2.9 billion kilometers away from the sun.

After the discovery of Uranus, scientists calculated its orbit, but the calculated results are not consistent with the observed results. They think it is caused by the gravitational interference of a new planet on Uranus.


In 1846, based on levier’s calculation of the orbit of the new planet, the astronomers Galle and darest of the Berlin Observatory successfully discovered Neptune, the eighth planet in the solar system. Therefore, at this time, the boundary of the solar system was extended to about 4.5 billion kilometers away from the sun.


In 1930, astronomer Thompson of Lowell Observatory discovered Pluto, which is more distant than Neptune, so he extended the boundary of the solar system to about 5.9 billion kilometers away from the sun.

But Pluto’s discovery did not end the exploration of the solar system’s boundaries.


After the 1940s, several astronomers have put forward an idea. They think that in the place far away from the sun like Pluto, the formation process of planets can not be carried out completely because of too sparse material distribution. Therefore, there is a Kuiper belt about 4.5-8.3 billion kilometers away from the sun.


Since 1992, the objects in the Kuiper belt have been released one after another. Their distribution is wider than originally estimated. The discovery of the objects has expanded the boundary of the solar system several times, but it is still not the boundary of the solar system.

Because astronomers generally speculate that there is an Oort cloud farther away from the sun. The Oort cloud is the most marginal cloud cluster in the solar system, wrapping the solar system like an eggshell. But it is very secret, it contains tens of thousands of celestial bodies, but its main part has never been observed, even in the foreseeable future, it is difficult to be observed directly, so how do we know it exists?


It mainly depends on speculation. Astronomers divide comets into two categories: short period comets (orbital period is less than 200 years); long period comets (orbital period is more than 200 years).


The orbit of long-period comets often extends to tens of thousands or even hundreds of thousands of astronomical units away from the sun.

In 1950, after analyzing the orbits of hundreds of long-period comets, the Dutch astronomer ault put forward a bold idea. He believed that there were a large number of small objects at tens of thousands to hundreds of thousands of astronomical units away from the sun, which were the source of long-period comets. If they happened to enter the solar system, they would become long-period comets.


The Oort cloud is made up of small objects, which are the source of long-period comets, so the Oort cloud is like a “big warehouse” filled with comets.


So how many small objects are there in the warehouse? It is estimated that there are several trillion, but this huge number is still very small compared with the vast space occupied by the Oort cloud. If a spacecraft passes through it, it is likely that it will not have a chance to approach any small celestial body.

For the formation of the Oort cloud, modern astronomers study that the Oort cloud was formed by the remnants of the formation of the major stars and planets after the formation of the solar system 5 billion years ago. For the specific formation, there is a hypothesis that is relatively easy to accept. Due to the gravitational effect of the big planets, the matter scattered in the galaxy will be thrown out of the ecliptic, forming a disk-shaped area, and finally forming a unique spherical shape around the solar system.


As for the hypothesis of the significance of the existence of the Oort cloud, some hypothesizes that the Oort cloud is the boundary of the solar system; some hypotheses that comets come from the Oort cloud; and some hypotheses that the Oort cloud will cause the destruction of organisms.


In a word, some specific aspects of the Oort cloud have not been clearly understood by human beings, but the research and exploration of the Oort cloud has never ended. Only on the basis of a better understanding of the solar system can we better explain the existence of the Oort cloud and provide a better basic guarantee for human beings to further explore the universe.

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