Catching up with centaurs to "read" the historical information of the formation and evolution of the solar system
2021-11-09
Compared with the common Jupiter family comets, centaurs have been in the Kuiper belt for a long time and receive less solar radiation, so they contain more primitive materials. Therefore, the study of centaurs can help us better study the material distribution and evolution of the solar system. Between the orbits of Jupiter and Neptune, there are tens of thousands of small objects composed of ice and rock. These small bodies are occasionally affected by Jupiter's gravitational disturbance, thrown into the interior of the solar system and fly to the sun and earth. Such small objects are considered to be the source of many Jupiter family comets and near earth comets. Because they have the characteristics of asteroids and comets at the same time, they are named centaurs. Recently, according to foreign media reports, scientists at the University of Chicago in the United States said that these centaurs near Jupiter may provide important clues to reveal the mysteries of the solar system. The researchers said that through in-depth analysis of centaurs, they found that the solar system is actually a dynamic planetary system and has been in a changing state. Where did Centaur come from? Can it tell us more about the secrets of the solar system? It is far and small, which makes it difficult to observe The formation of the solar system began with a primitive Nebula 4.6 billion years ago. After accretion, aggregation and evolution, some of the original materials in the nebula have merged into eight planets, and some are still loosely distributed in several banded areas of space. The small objects in these banded areas are the evidence left by the early evolution of the solar system. Most asteroids in the solar system are the stars of the primitive solar nebula, which existed in the early stage of the formation of the sun. The Kuiper belt outside Neptune's orbit is such a region, in which there are about 100000 celestial bodies with a diameter of more than 100 kilometers. The celestial bodies in the Kuiper belt are mainly composed of frozen low boiling mixtures, mainly composed of water, ammonia and methane. There is also an asteroid belt between Mars and Jupiter. The celestial bodies here are mainly composed of rocks and metals. Compared with the two asteroid belts, the Centaur group between Jupiter and Neptune is less known. "Centaurs are small objects whose semimajor axis and perihelion are between the orbits of Jupiter and Neptune. Most centaurs originated in the Kuiper belt. In recent millions of years, their orbits have changed and become today's centaurs." Shi Jianchun, an associate researcher at the Zijinshan Observatory of the Chinese Academy of Sciences, told Science and technology daily, At present, 452 Centaur objects have been discovered. The first Centaur object discovered is called "944 Hidalgo", which was discovered by German scientists in 1920. At present, the largest Centaur object "10199 chariklo" with a diameter of about 260 kilometers was discovered by American scientists in 1997. In about a century, why are only 452 Centaur objects "captured" by humans? Shi Jianchun explained: "the Centaur is far away from the earth, and its perihelion is outside the orbit of Jupiter, that is, it is also outside the orbit of Jupiter when it is closest to the earth. In addition, it is generally small and dark, so it is difficult to find." In addition, Centaur is a transitional object between Kuiper Belt objects and Jupiter comets, and its orbital region is dynamically unstable. "The orbits of centaurs are easily disturbed by the gravity of giant planets such as Jupiter, and their orbits change," Shi Jianchun said. Centaurs can provide "unique" clues Shi Jianchun introduced that some centaurs show the same activity as comets, with coma and tail. Comets are generally composed of three parts: nucleus, coma and tail. The comet core is composed of ice material. When the comet approaches the sun, the comet material sublimates and forms a hairy coma and a long tail around the ice core. "Because centaurs have been outside Jupiter for a long time, there are many volatile components attached to celestial bodies, such as carbon monoxide ice and carbon dioxide ice. When the temperature rises and the volatile gas ice sublimates, the dust trapped on the surface of celestial bodies will be released and reflected by sunlight, forming comas and tails similar to comets we see," Shi Jianchun said. According to media reports, in this study, Seligman, a postdoctoral researcher at the University of Chicago and the corresponding author of the paper, said: "These materials are very old and contain ice that has never been melted in the early solar system. Comets are interesting not only because they are beautiful, but also because they can provide humans with a way to detect the chemical composition of materials in the distant solar system." In Shi Jianchun's view, different from ordinary comets, the characteristics of centaurs provide a "unique" clue for us to study the evolution of the solar system. "Compared with the common Jupiter family comets, centaurs have been in the Kuiper belt for a long time and receive less solar radiation, so they contain more primitive materials. Therefore, the study of centaurs can help us better study the material distribution and evolution of the solar system." Shi Jianchun said that in addition, because the perihelion of centaurs is outside the orbit of Jupiter and the temperature is low, its activity mechanism is different from that of Jupiter family comets. The activity mechanism of Jupiter family comets is driven by the sublimation of water ice, while the activity mechanism of centaurs is driven by the sublimation of gas ice and cannot be explained by the volatilization of water ice. Therefore, through the study of centaurs, scientists can The similarities and differences of comet activity driven by water ice sublimation and gas ice sublimation are compared. According to media reports, in this study, scientists studied the number of Centaur objects and the mechanism by which these objects occasionally become comets flying to the sun. They estimated that about half of Centaur comets were pushed into the solar system by interacting with the orbits of Jupiter and Saturn; the other half were trapped in the orbit of Jupiter because they were too close to Jupiter, and then died because of The influence of Jupiter's gravitational disturbance is thrown towards the center of the solar system. The latter mechanism provides a perfect way to better observe these centaurs that are about to become comets. As proposed in this study, launch a spacecraft to Jupiter and let it run in Jupiter's orbit until the Centaur crosses Jupiter's orbit. Then the spacecraft can fly in the process of the Centaur flying towards the sun and becoming a comet Observation. It is not difficult to realize "keeping the plant and waiting for the star" This idea of "keeping plants and waiting for Stars" is not a fantasy. "The method of waiting for centaurs in Jupiter's orbit is indeed feasible." Shi Jianchun believes that mankind's current space launch technology is quite mature, and it is not difficult to send spacecraft to Jupiter. At present, many spacecraft have flown to the outer solar system; the Juno spacecraft of the National Aeronautics and Space Administration (NASA) of the United States only took about five years to reach Jupiter, and is currently taking pictures of Jupiter. In addition, even when small objects move, it is possible for humans to visit them. For example, the US Osiris Rex probe visited the Benu asteroid 200 million miles away; Japan's Falcon 2 probe brought back some rock samples from another asteroid, Longgong. "However, this is not the only comet observation scheme. Different observation schemes can be formulated according to specific scientific objectives. For example, for the famous Centaur comet 29p / schwassmann wachmann, orbit can also be designed separately for flying around observation," Shi Jianchun said. This will be an imaginative picture: the ice in the comet is composed of different types of molecules and gases, which begin to burn at different points in the process of reaching the sun; the Spacecraft flies around the comet, it "looks" at the formation process of the comet and knows what the comet is composed of by measuring the comet tail. Seligman said that through this method, scientists can find out when the typical comet ice began to burn and the detailed internal structure of the comet. There is little hope to find out these from ground telescopes. At the same time, the surface of comets will erupt and form craters with the increase of temperature. Seligman said that understanding these phenomena will help scientists better understand the solar system. It is very important to understand how to form earth like planets in the solar system. Shi Jianchun has the same view on this. He believes that: "tracking and observing the process of a centaur from a small planet into a comet and developing a coma and tail is helpful to study the activity mechanism of comets and the composition distribution of water and other substances in the early solar system, so as to reveal the formation and evolution history of the solar system." (outlook new era)
Edit：He Chuanning Responsible editor：Su Suiyue
Source：Sci-Tech Daily
Special statement: if the pictures and texts reproduced or quoted on this site infringe your legitimate rights and interests, please contact this site, and this site will correct and delete them in time. For copyright issues and website cooperation, please contact through outlook new era email：lwxsd@liaowanghn.com
Sci-Tech
Recommended Reading Change it 
Home
