How many exoplanets are really suitable for human habitation in the universe?

A paper published in the Journal of the Royal Society shows that a Swedish research team has re-investigated the exoplanets that have been discovered by humans through new methods; 45 exoplanets were screened out. They are not only similar in mass to the earth, but also similar in atmospheric composition. It is absolutely certain that liquid water can be maintained on them.

If there is no mistake in this study, these 45 exoplanets, if you think about it in your mind, are exactly the same as the earth you see in space; The blue sea, the white clouds, the clear atmosphere and the acceleration of gravity are almost the same as those of the earth, so you can't tell them from the earth at all. When you land inside these planets, you may see the difference. They may have no signs of life, and the whole planet is Wang Yang.

However, according to our previous knowledge, it is hard to imagine that a planet with the same environment as the earth is lifeless. So to a large extent, you should be able to see large buildings that are not naturally formed on it. At night, the whole planet is brightly lit. They are alien natives. At this time, you are likely to be invited as an alien invader? Guest? . In recent years, I believe you have a deep feeling that we humans are more cautious about alien life than in the last century. When you look back on the last century, we deliberately sent radio signals to outer space.

For example, the Arecibo Observatory in the United States has a spherical radio telescope with a diameter of 305 meters. It used to be the largest radio telescope with a single aperture on the earth, and later it reached 500 meters in diameter in China. Eye of the sky? Beyond. 1974, to celebrate the anniversary of 10, it is like a globular cluster M 13, which is 25,000 light years away from us. The general meaning of the signal is: hello, alien brothers, we are human beings. Look at our body structure. Look at our position here. Are you interested in being friends?

The star density of cluster M 13 is very high. Scientists believe that the probability of alien life is still quite high, so they choose to send signals to this cluster. However, it will take at least 50 thousand years for this signal to be received by alien life and then give us feedback. However, if you take the initiative to expose your behavior, it is very likely that you will not get it back in the future: hello! But a huge interstellar fleet. Besides sending signals to other planets, we also like to give gifts to extraterrestrial life. For example, in the 1970s, we launched Voyager, which contained a record with a lot of information about human beings.

At present, this information has been sent to the interstellar space 22.2 billion kilometers away from the earth. Perhaps this gift is also returned by the huge starfleet. Therefore, after human contact with alien life, many scientists are trying to stop this stupid behavior, the most representative of which is Hawking. Entering the 2 1 century, many scientists not only believe in the existence of alien life, but also believe in the so-called? Dark forest law? .

So now we rarely, or simply stop taking the initiative to contact with alien life, which is meaningless and quite dangerous. Instead, the focus of the work is to find exoplanets suitable for human survival. This work is very difficult, mainly because the planet itself does not emit light, or it can only reflect weak visible light or emit weak infrared light. However, because the distance is too far, the probability of directly observing exoplanets is very small, so we can only find them by simple introduction and study their properties.

For example, the Kepler telescope, which was launched and retired by NASA, and the TESS telescope, which took over its work in 20 18, are doing this. Are telescopes that can work in the near infrared band. We have long established a scientific model of the birth of planetary system, which is based on the observation and research of our own solar system. As long as there are molecular clouds containing various heavy elements in space, they can become the place where planetary systems were born. First of all, this cold molecular cloud will collapse into a primitive planetary disk under its own gravity; While this process is going on, the places with higher local density in the molecular cloud will attract more substances; Know that somewhere, matter first gathers enough to ignite nuclear fusion and stars are born; The birth of the star provided a center of gravity for this originally chaotic place, which made the protoplanetary disk start to move regularly under the action of the center of gravity. The planet is in the planetary disk because of uneven density. Is the above theory of planetary system formation correct? Ok, because we have seen the protoplanetary disk when the planetary system was formed in the universe through infrared or microwave/radio bands, and we have also seen the planetary disk in it? Gap? These gaps are the process of the birth and movement of planets.

Observations have confirmed that our theory about the formation of planetary systems is correct. As the newly formed planets have not cooled down, we can see them in the long wave band. But if a mature planetary system, such as our solar system, has completely turned cold, what do we think of them? There are two main methods:

Planetary transit: the planet will pass through the disk of its parent star in a certain period, and we will see the faint luminosity change of its parent star. According to its motion period and the mass of the parent star, we can calculate some orbital parameters such as the mass, radius and distance of the planet. Star wobble method: When some massive planets orbit their parent star, the parent star will also rotate around its same center of mass, so that we can observe that the spectrum of the parent star will shift red and blue in a certain period. Then calculate some corresponding parameters.

This is the way we used to look for and study exoplanets, and we can know their mass, the nature and orbital distance of their parent stars, so as to judge whether they have their own atmosphere, whether they are in the livable zone of their parent stars and so on. Through the above methods, we have discovered more than 3,500 exoplanets, most of which are 1 times or twice the mass of the earth, and their volumes are basically between Uranus and Neptune. What are these planets? Super earth? . Of course, there are also some gas giants similar to Jupiter, even bigger than Jupiter. Another interesting discovery is that most exoplanets are not as regular as the solar system, with four rocky planets inside and four giant planets outside. In amateur galaxies, any planet, even a rocky planet with a small mass, may orbit its parent star at any distance, and some gas giants are very close to their parent star, and there are various situations.

In the past, we studied whether an exoplanet was livable, mainly by looking at its mass and whether it was in the livable zone of its parent star, and then we decided whether it was so-called livable. Earth 2.0? . This method has great defects and is not accurate enough. The researchers who published this new paper analyzed the composition of the planetary atmosphere by studying the spectrum of the planetary atmosphere, and studied the gravity and atmospheric temperature of the planet according to the escape velocity of the planetary atmosphere, that is, using gas dynamics. See how similar they are to the earth.

Using the above method, scientists first analyzed 55 exoplanets that we thought might be livable before, and found that only 17 of them met the new standard, and then analyzed other planets that were previously considered uninhabitable, and found that 28 new planets met the standard. In this way, using new scientific means, scientists screened out 45 Earth-like planets from previous data. Their mass, atmospheric composition and temperature are comparable to those of the earth. They have liquid water, suitable atmospheric temperature and the same acceleration of gravity. Is it? Earth? . You may ask, what's the use of finding these planets? In fact, even if we have confirmed that these planets can support life, we have no way to prove that there is life on them. Can only rely entirely on speculation.

However, finding these livable planets can let us know that there is more than one cradle like the earth in the universe, which is very common. Explain that the earth is not special, just one of many accidents. Secondly, finding these planets can prepare for the future of mankind. Now we can't travel and emigrate, but we can definitely do it in the future. One day, the earth will no longer be suitable for living, which leads us to choose some planets that are most suitable for emigration according to the study of exoplanets by human beings in.