The light emitted by the sun "travels" for more than 8 minutes to reach the Earth. Have you ever wondered how big the solar system is? Where are its edges?
Some people think that Pluto is Pluto, because Pluto's distance from the Sun is about 40 times the distance between the Earth and the Sun, and it takes 5 hours and 30 minutes for light to reach there from the Sun.
As scientists continued to dig deeper, it was discovered that Pluto was far from the boundary of the solar system. If we continue to look outward, we will find that there are many asteroids, thousands of meters in diameter and thousands of kilometers in diameter, and this area is called the Kuiper Belt.
Is the Kuiper Belt the edge of the solar system? Nor is it.
The latest research suggests that the farthest point within reach of the Sun's gravitational pull is the Oort Cloud, which is 50,000 to 100,000 ASTRONOMICAL units from the Sun and is more than 1 light-year away.
So what is the Alter Cloud? What are its features?
In the 1950s, Ault came up with a very bold conjecture: at the outermost periphery of the solar system, there was a huge globular cloud of gas, the so-called Oort cloud, which was a huge ice reservoir containing not only a large amount of crushed ice, ice cubes, but also a large amount of methane. Its radius is about 15 trillion kilometers, which is 100,000 times the distance from The Earth to the Sun and more than 300 times the radius of the solar system as traditionally believed. It is bound by the sun's gravitational pull, so it is still part of the solar system.
But to this day, no direct evidence of the existence of this Oort cloud has been found. But because it explains the origin of comets in the solar system so well, almost no one would suspect the existence of the Oort cloud now.
Comets are small objects that approach the sun once in a while and then fly farther away, and most comets are thought to come from the Ault Cloud.
Comets have a long tail when they approach the Sun, because when small bodies enter the interior of the solar system and approach the Sun, some of their components will sublimate from solid to gaseous, a luminous core to form a comet nucleus, and the dust sublimated into gas becomes a luminous coma or comet tail.
But, have you ever wondered how a comet is so small that the volatiles on it will soon be used up, and how it can be so stable for billions of years? For example, Halley's Comet, which approaches the Sun once every 76 years, how does it remain stable?
This brings us to the Oort cloud.
In theoretical hypotheses, the Ault cloud is the equivalent of a comet's "gas station." When some comets fly to a point far away from the sun, they actually go back to the Oort cloud to "refuel". There is a large amount of methane and other material in the Oort cloud, and comets enter the Oort cloud to replenish this material.
Now do you understand what an Alter cloud is?
This article is scientifically checked by Wang Heyi, a first-level teacher at the Second Branch of the Affiliated Middle School of Chinese University.