Beijing time, January 8th news, according to the physicist organization website report, when you look at the starry sky at night, what do you see? Stellar, no doubt. But beyond that, there are actually countless planets and billions of planets. This is based on the results of a recent study conducted by the California Institute of Technology in the United States, which further proves that planets are very common in the universe. The scientists of the research team have studied a planetary system, that is, the planetary members of Kepler-32. They believe that this planetary system is representative, so it can be used as a perfect sample to study how most planets are formed.

John Johnson is an assistant professor of planetary astronomy at the California Institute of Technology and a co-investigator of this research. Their paper has recently been accepted by the Astrophysical Journal. He said: "There are at least 100 billion planets in our galaxy, at least." For this, Jonathan Swift, a postdoctoral researcher at California Institute of Technology, said: "It sounds incredible. If you If you think about it carefully, this is indeed an eye-popping number: almost every star in the Milky Way can be divided into a planet. "And this time there are 5 planets in the Kepler-32 system used by the research team as a sample. However, the existence of only two planets has been confirmed, and the existence of the remaining three planets is still in doubt.

The California Institute of Technology's research team first confirmed the existence of three other planets in the system, and then compared it with other exoplanet systems discovered by Kepler telescopes. The five planets are orbiting an M-type red dwarf star. The number of such stars is the largest. They occupy almost 3/4 of the stars in the entire Milky Way. These five planets are about the same size as the Earth, but the distance around the stars is much shorter than the distance between the sun and the earth. These conditions are very typical of the planets found around M-type stars in other situations. Therefore, most of the planetary systems in the Milky Way may have similar properties to these five planets. So since this planetary system is so common and typical, why did the research team choose it as the research object? Why can it stand out in the screening? The reason for this is related to the unique orientation of this planetary system: it happens to be oriented sideways The earth, so when we observe from the earth, every planet in this planetary system will successively obscure the star in its center, so that its existence is detected by the Kepler telescope.

Through the research and analysis of planets covering the stellar light, scientists can determine important information such as planet size and orbital period. Because of the unique orientation of this planetary system, scientists have an excellent opportunity to study the system, and because scientists believe that these planets are very representative, then research on the system will help scientists We understand the general formation mechanism of most planets in our galaxy. Jonathan said: "I try to avoid calling it the Rosetta Stone, but this is really the closest case I have ever seen to the nature of the Rosetta Stone." He said: "It's like mastering something The new language we have been trying to understand is the language about planet formation. "And a very important basic question on the topic of planet formation is: how many planets exist in the Milky Way?

Like the California Institute of Technology ’s research team, other research groups have previously estimated that the number of planets in the Milky Way is about one planet per star, and this is the first time that astronomers have reached this conclusion by studying M-type stars. Such stars are the most numerous in galaxies. In order to carry out the relevant calculations, the Caltech team first estimated the likelihood of a M-type dwarf star having a planetary system with a lateral orientation similar to Kepler-32. Using this estimate, along with other observations obtained by the Kepler telescope, the team estimates that, on average, such a possibility is about one planet per 100 billion stars. However, their estimates only take into account the situation of orbiting stars at close distances, and do not consider the situation of other planets with longer orbits or planets orbiting other types of stars.

Therefore, the research team stated that the estimates they gave were conservative. In fact, as Swift put it, a more accurate estimate, combined with data from other sources, should yield about two planets per star. The Kepler-32 planetary system orbiting an M-type dwarf star is very special compared to our solar system. Just to say a little bit, the heat and mass of M-type stars are much smaller than our sun. For example, the star Kepler-32 has only half the mass of the sun and half the radius of the sun. The radius of the five planets orbiting them is not large, roughly between 0.8 times and 2.7 times the radius of the earth, and the orbits of these planets are very close to the stars. Their orbital distance is generally less than 1/10 AU (AU is the astronomical unit, equivalent to a sun-earth distance), such a short distance is almost equivalent to 1/3 of the distance from Mercury to the Sun.

For Jonathan, the fact that the number of M-type stars far exceeds that of other types of stars is of great significance, that is: galaxies like our solar system are very rare. He said: "This is very strange." Astronomers also pointed out that those planets that are very close to the "Sun" do not mean that it is a very high temperature purgatory and not suitable for life. The two cannot be equal. In fact, due to the low mass and low temperature of M-type stars, the habitable zone around them-that is, the temperature-appropriate area that can allow liquid water to exist on its surface, is much closer to its body than stars such as the Sun. Although for the Kepler-32 case only the outermost planet fell into the habitable zone, other M-type stars had more planets falling within the habitable zone.

As for how the Kepler-32 planetary system is formed, no one knows yet. However, the research team said they have given some restrictions on this issue. For example, their results show that these planets were formed farther away from the sun than they are now. It was later that their orbits became so close to the stars. Like other planets, the planets orbiting Kepler-32 also originated from the original dust gas planetary disk. Astronomers estimate that the amount of dust gas in the area where the five planets are located is approximately equivalent to the mass of three Jupiters. However, other researchers believe that it is impossible to have as much gas and dust material as close to the stars, because the California Institute of Technology tends to think that these planets first migrated to planets after they were formed farther away from their sun. Department of the inner side.

It is also worth noting that M-type dwarf stars emit brighter heat than the later levels in the early stages of their life, that is, when the planet begins to form. The distance between the Kepler-32 planetary systems was too close, and it was impossible for these planets to even form in the temperature environment at that distance. Prior to this, other researchers pointed out that the density of the third and fourth planets in this planetary system seems to be low, and may contain many volatile substances, such as carbon dioxide, methane or water ice and other gases. However, all these volatile substances cannot be formed so close to stars. In addition, astronomers also found that the orbital period of three of these planets is very unique, and they have formed 1: 2 and 1: 3 orbital resonance relations between them.

Jonathan pointed out that planets will not automatically form this periodic resonance relationship when they are formed. In other words, these planets must have formed at other distant locations before moving inward to their current location. Jonathan said: "If you look closely at some details of this unique planetary system, you can't help but think that these planets must have migrated to their internal positions after they were formed at a distant location."

The researchers pointed out that realizing the fact that a galaxy is actually full of planets will have far-reaching significance. In response, Swift said: "This is a very fundamental problem from the point of view of origin." He also pointed out that because M-type stars emit radiation mainly in the infrared band, it is difficult for us to observe them in the visible band. He said: "With the help of the Kepler space telescope, we learned that the number of planets in the sky far exceeds the total number of stars we can see."

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