In ancient times, people knew that there was a more mysterious world outside the earth, but because of the lack of scientific assistance, the ancients did not know what the world outside the earth looked like? In the eyes of the ancients, the stars at night are things in the world outside the earth, and this world is also very beautiful and prosperous, with a large number of immortals living.
With the continuous development of human civilization, we embarked on the path of technological development hundreds of years ago. With the help of scientific power, we invented the astronomical telescope and initially saw the hopeful world outside the earth, but in the eyes of the telescope, the space of the earth is dark and not as beautiful as we imagined. scene.
By the middle of the last century, with the help of science and technology, mankind finally realized the dream of flying out of the earth. After we walked out of the earth, we finally saw this extraterrestrial space that countless people looked forward to. We call it the universe.
Observed by the naked eye, the entire universe is vast, vast and dark. Except for the places where some stars can emit light, the background of the entire universe is pitch black. So is the universe really dark? Of course not. What we see through the astronomical telescope is another scene, that is, the bright light everywhere in the universe, that is the light emitted by each star.
Astronomical telescopes can see far away, but we still need detectors to explore the mysteries of the universe. For human beings who have just stepped out of the earth, the first thing is to explore the mysteries of the entire solar system, and the most mysterious and complex area of the solar system is at the edge of the solar system.
In order to explore the edge of the solar system, NASA launched Voyager 1 and Voyager 2 in 1977. Their goal is to keep advancing outside the solar system, not only to explore the mysteries of the edge of the solar system, but also to go out of the solar system and enter the interstellar space for exploration.
In the eyes of scientists, the distribution of matter in the universe is not the same. In some places, there is a lot of matter, and the density is greater, while in some places, the matter is smaller and the density is lower. Theoretically speaking, the closer the area of the star system to the sun is, the greater the density of matter should be, and the greater the density of matter in areas far away from the edge of the solar system.
In the interstellar space outside the galaxy, there is very little matter, so we say that the universe is a vacuum space. But this vacuum is not absolute emptiness, I believe my friends are very clear about this. In our seemingly empty universe, there will always be some particles. Even in the cosmic hole observed by an astronomical telescope, it is not completely free of celestial bodies and matter, but it is so small that we cannot observe it.
In theory, the interstellar space should be more empty, and the density of matter is much lower than that of the inner solar system. Is this really the case? This answer may have to rely on the Voyager to complete. After decades of flying, Voyager 1 was the first to reach the edge of the solar system, crossing the top of the heliosphere in 2012. On the other hand, Voyager 2 will pass through the top of the heliosphere in 2018 and enter interstellar space sooner or later.
After the Voyager spacecraft arrived at the edge of the solar system, it also sent a series of important detection data back to the earth. These data are very important for scientists to understand the matter of the edge of the solar system and are also an important reference for our initial understanding of interstellar space.
Earlier we talked about the concept of the heliosphere. Maybe many friends don’t understand what this means? Here is a brief explanation. The so-called heliopause refers to the place where the solar wind and the interstellar medium meet. We all know that the solar wind is the strong radiation emitted by the sun, which spreads and extends around the solar system.
The areas that the solar wind can reach belong to the solar system in a narrow sense. As the solar system continues to spread to the edge, its strength is also constantly weakening, and it will meet with the interstellar medium from the interstellar space at the weakest point. So what does it look like when the solar wind does not meet the interstellar medium? This is something that scientists really want to understand.
Back to the topic of cosmic matter density. In the solar system, the average density of protons and electrons in the solar wind is 3-10 per cubic centimeter. The farther away from the sun, the lower the density. According to previous calculations, the average electron density of the interstellar medium in the Milky Way is about 0.037 electrons per cubic centimeter, and the plasma density outside the heliosphere is about 0.002 electrons per cubic centimeter.
The above data is a result calculated theoretically by scientists. To verify this result, we need the real data detected by the Voyager. When the two Voyager spacecraft crossed the top of the heliosphere, the detectors carried on them successfully detected the electron density of the plasma.
, Voyager 1 detected 0.055 electrons/cubic centimeter at 18.3 billion kilometers, and Voyager 2 detected 0.039 electrons/cubic centimeter at 17.9 billion kilometers. The two values are basically the same. But when Voyager continued to fly in interstellar space for a while, the data returned by the probe surprised scientists.
Theoretically speaking, once Voyager crosses the heliosphere and enters interstellar space, the detected material density should be very small. After all, it is interstellar space, and the material density cannot be compared with that in the solar system. However, after Voyager 1 has flown 2.9 billion kilometers in interstellar space, the density of interstellar medium detected is 0.13 electrons/cubic centimeter, which is much larger than when it crossed the heliosphere.
After Voyager 2 has flown 600 million kilometers in interstellar space, at 18.5 billion kilometers, the density of the interstellar medium has also increased to 0.12 electrons/cubic centimeter. The values of the two exploration spacecraft are basically the same, which shows that the data detected by the Voyager spacecraft are real and reliable. The density of matter in the interstellar space outside the solar system is indeed very high. What is going on?
For this result, scientists are also puzzled. The density of matter in interstellar space is less than the density of matter in galaxies. This should be a correct conclusion. But why is the situation in the interstellar space outside the solar system so special? Some scientists have proposed a possibility that when the interstellar magnetic field lines cover the top of the heliosphere, the magnetic field lines will become stronger, which may form a kind of electromagnetic ion cyclotron instability and deplete the plasma in the covered area. .
There is also a view that the matter blown by the interstellar wind is blocked and decelerated at the top of the heliosphere, which causes a certain degree of matter to be unable to diffuse out and gather in a limited range. If this is the case, then as long as the Voyager travels a little further forward, it may be able to detect the actual density of interstellar space.
In fact, here we have to think of another possibility, that is, the space beyond the heliosphere may not be the real interstellar space. They still belong to the solar system, that is, the solar system in a broad sense. In the past, scientists believed that going out of the heliosphere meant going out of the solar system into interstellar space. However, scientists later observed the existence of the Oort Cloud, and believed that only when they stepped out of the Oort Cloud can they be considered as truly out of the solar system.
The Oort Cloud is a nebula with a thickness of one light-year, which surrounds the solar system in a narrow sense. In this nebula cluster, there are not only a large number of comets, asteroids and other celestial bodies, but the density of matter is much higher than that of interstellar space. Therefore, it may be understandable that the Voyager spacecraft walked out of the heliosphere, but detected a higher density of interstellar medium.
If the Voyager spacecraft remains at a high level in the density of the detected matter during the subsequent flight, then it is a high probability event that they are still staying in the solar system. And such a result plays an important role in our understanding of the solar system, at least it allows us to understand that the range of the solar system is much larger than previously imagined.
Of course, if the outside of the Oort Cloud is considered interstellar space, it will also disappoint scientists, because Voyager also shoulders an important task, which is to find alien civilization. They all carry a golden compact disc, which records the coordinates of the earth and human information.
Scientists expect Voyager to get out of the solar system and be very lucky to be captured by an alien civilization, and then the alien civilization will come to the solar system to come into contact with humans through the information left on the disc. Now it seems that this wish is basically hopeless, and it will probably take at least 10,000 years to cross the Oort Cloud at their speed.