"Alien" in the near -ground asteroid track

We know that in addition to the eight major planets, we also wander a small asteroid and comet at the rice level to 100 kilometers. As of now, the small sky body that has been discovered has nearly 1.2 million (most of them have not observed activity, belonging to small asteroids), and the number is still increasing year by year.

The orbital position distribution of the inner solar stars that have been discovered at present | Source: Author

Most of the asteroids are located in the asteroid belt between Mars and Jupiter, called the main asteroid. Generally speaking, these cute asteroids will run safely on their orbit on their orbit. They have nothing to do with each other, but there is always a certain probability that they collide with each other and produce a large amount of fragments of different orbit. In addition, under the action of the gravitational disturbance of large planets and complex thermal physical effects, the orbit of the asteroid may migrate and even migrate to the near -ground space. Astronomers are classified as asteroids that are less than 1.3 AU (AU are astronomical units, and the average distance of the daily land) are classified as near -place planets.

Compared to the main asteroid, the near -earth asteroid may not be so cute, because their tracks will change more severely and frequently during the evolution, and even intersect with the earth's orbit. It is called potential threat near -earth planets with a diameter of more than 140 meters and a minimum meeting of the earth within 0.05 AU, and 2275 are found). Therefore, astronomers from various countries pay close attention to the asteroids.

Potential threats nearly discovered nearly small asteroid track distribution | Tap source: Author

On March 11, 2022, a near -earth stars numbered 2022 EB5 were observed two hours before falling into the earth. Fortunately, this asteroid was only about 1 meter size. The burning was destroyed, let us be shocked.

2022 EB5's track before hitting the earth (in order to better reflect the three -dimensional effect, the vertical line of the asteroid track towards the zodiac surface) | Source: Astorb.com

It is precisely because the near -earth asteroid can cause potential security threats to the earth, so precise determination and forecasting of their tracks is an important research topic. However, the content of this aspect is not the theme of this article. Readers to understand the track configuration of near -ground asteroids, especially some strange and interesting cases.

In fact, astronomers have half a long axis based on the elliptical orbit of near -earth asteroids, and they are divided into four categories in the long -distance and long -distance distances: Ammore, Aden, Apollo -type and Arina. Here we do not start these classifications, and interested readers Baidu can understand their differences. This article mainly focuses on some small planets with extreme orbit characteristics or special rail geometric formats.

2017 UR52 — Three Record Standers: the most flat track, the longest cycle, and the largest long -distance distance

First of all, let us offer a near -earth planet 2017 UR52 that broke three "world records". The asteroid diameter is about 200 meters. When discovered, the asteroid was approaching the recent point, with a speed of 37 kilometers per second. The rail cycle of the 2017 UR52 exceeds 5,000 years, which is the longest -plated small planet that is currently found the longest (meaning the largest long diameter); in addition, the eccentricity of this asteroid reaches 0.9957, which is currently the most flat orbit currently discovered rails. Small planets; Finally, combining its maximum length and maximum eccentricity, it can be inferred that it is also the largest near -ground planet that is currently discovered. Note. In fact, the orbit type of the 2017 UR52 is similar to the long -term comet. However, because it was not found to be active when it arrived near the nearby point, it was not classified as a comet.

Near -ground planet 2017 UR52's track schematic | Source: Astorb.com

2005 HC4 -Two record holders: the smallest distance and the fastest running

2005 HC4 was a near -ground planet found by the Lowell Observatory on April 30, 2005, with a diameter of about 250 meters. The eccentricity of this asteroid is also very high, reaching 0.961, and the distance reached 0.071 AU. It is the smallest near -ground planet currently discovered. It is 0.23 times that Mercury and the sun distance. hot). Considering that its long diameter is 1.821 AU, it can calculate that it has a speed of 157 kilometers per second at the time of the recent point.

Near -ground planet 2005 HC4's track schematic | Source: Astorb.com

2021 pH27 — the shortest orbit cycle

In contrast to the 2017 UR52, a near -ground planet 2021 pH27 (about 1 kilometer in diameter) discovered on August 13, 2021 has the shortest track cycle. Only 0.314 years. The asteroid is completely within the orbit of the earth, so it is also called a small planet in the earth. However, from the perspective of the Earth observer, because the relative angle between the asteroid and the sun is small, there are relatively few observation opportunities. Generally, when the asteroid reaches the far away point and the earth is just in the right place, can Watch it near dawn or dusk. Small planet 2021 pH27's track schematic | Source: Astorb.com

"Wind and Rain Rebellion" -The retrograde small planet

We know that most of the large planets in the solar system are close to 0 °, and the phenomenon is "smoothly" around Japan. This phenomenon is related to most material in the early formation of the solar system. Most of the near -ground asteroids are also "smooth" (the orbital inclination angle is less than 90 °), but there are still a small part of the near -earth asteroid under the complex mechanism that appears more than 90 °. Small planet. There are currently five known asheric stars in this kind of near -ground stars: 2014 PP69 (inclination angle 93.7 °), 2017 UR52 (inclination angle 108.3 °), 2019 EJ3 (inclination angle 139.8 °), (343158) Marsyas (inclination angle 154.4 °) and 2020 BZ12 (Inclusive angle 165.5 °).

Some studies have shown that asteroids and Jupiter's 3: 1 track resonance (that is, the ratio of the track cycle of Jupiter and asteroid is 3: 1) may be the cause of such small asteroids. The orbit evolution of the consequences of comets. In fact, in addition to the near -ground asteroid, the total number of other types of retrograde stars that has been found in the solar system has reached 122. These "retrograde" are very interested in researchers in the field of celestial physical skills. Migration mechanisms, track life, distribution characteristics, etc. have carried out various research.

Small planet 2020 BZ12's track schematic | Source: Astorb.com

"Inner Cut"/"outer Cut" small planet

Next, let's consider two kinds of small planets with a special near -ground geometry: "inner cut" and "outer cut" small planets. The "inside cut" or "external cut" here is relative to the earth's orbit, that is, the asteroid track is cut from the long -day orbit of the earth (long -day or long distance between 0.983 ~ 1.017 AU). For example, (325102) 2008 EY5 and (100085) 1992 UY4 belong to the former and the latter. Although they seem to be "beautiful" in track geometry, they are potential threats to the earth's security. Considering the situation of the eccentricity rate greater than 0.2, the number of "external cuts" types of near -land stars that have been discovered have reached 2,319, while the number of "internal cuts" type is only 66. The former is 35 times that of the latter. The difference between the disparity quantity is related to the distribution of their real quantity, but it may also be related to the "selection effect" in observation.

Small planet near the ground (325102) 2008 EY5's orbital schematic | Source: Astorb.com

Small planet 1992 UY4's track schematic | Source: Astorb.com

2016 HO3 —— The "quasi -satellite" on the earth

If the orbital cycle of a near -earth asteroid is very close to the earth, that is, a 1: 1 track resonance is formed, and it is called the earth's co -orbit planet. Because there is a certain eccentricity rate on the earth's orbit, the velocity of the around -Japan movement angle is not constant; considering that the asteroid track often has a certain eccentricity rate, this eventually leads to The movement of the earth may be recovered. And if the center position of the cycle is just near the earth (if the center location is located at the Japanese triangle tingling point 60 degrees near the earth's orbit, the asteroid is called the Earth "Troy" asteroid), then from the earth It seems that the asteroid turns "around" the earth. This kind of small celestial body is called the "quasi -satellite" small planet of the earth. This is because this phenomenon is mainly a rail geometric effect. It is really a rail movement around the earth under the dominance of the earth.

At present, the "quasi -satellite" asteroid of the earth has discovered five, and the most famous is about 40 meters in diameter (469219) Kamoʻoalewa (or 2016 HO3). It is planned to land on the asteroid and collect research samples to bring back to the earth. The 2016 HO3 is the best orbit stability in the five quasi -satellites. It is expected that it can still be maintained in the "quasi -satellite" state in the next 300 years, and it will still be a common rail with the earth in the next 1 million years.

The schematic diagram of the rails of the next 100 years in the next 100 years in the next 100 years in the next 100 years of the next 100 years of the schematic diagram of the Japanese -ground rotation system | Picture Source: Astorb.com

2020 CD3 —— "Mini Moon"

If a near -earth asteroid breaks into the earth's moon system at a relatively low speed, it may be captured by the earth moon system to become a natural satellite on the earth. However, because the arrested asteroid track energy is still relatively large, generally speaking, it will evolve over time to escape the restraint of the gravitational gravity of the earth. Therefore, such small asteroids can only be regarded as temporary satellites of the earth. The 2020 CD3 discovered by Cartelina Sky Tour on February 15, 2020 belongs to this kind of near -ground planet (it is estimated that the diameter of the small planet is only about 3 meters). According to the calculation of its track traceability, it was found that the asteroid was captured by the gravity of the earth moon system around September 2017, and then in a complex gravitational environment for the Earth for orbit movement, and left the place in May 2020 Moon. After the discovery of the asteroid, it caused great interest in the public, and was once known as the "mini moon" of the earth.

2020 CD3 (purple) is captured by the earth (blue dot), and yellow represents the moon track. | Picture source: wikipedia

2010 TK7 and 2020 XL5 -Earth Troy Star

On the surface of the earth, the position of the 60 ° angle between the earth and the 60 ° front and after the earth is called the day-earth triangle flat (or the Japanese-Eraglan day L4 and L5 points). If a small asteroid moves near the Japanese-earth triangle, such a small asteroid is called Earth's Troy asteroid. Compared with the daily-wood triangle flat moving point, the stability of the daily-earth triangle leveling point is poor, so it is generally difficult for small asteroids to stay here for a long time. For a time, people thought that there was no Troy asteroid similar to Jupiter on the earth. Until October 2010, the Wise Space Telescope in the United States first discovered a Earth Troy asteroid at about 300 meters near L4. Studies have shown that 2010 TK7 may be "captured" nearly 1800 years ago near the Earth L4 point, and after 15,000 years, it may be migrated near L5, and it may no longer "escape" and no longer become the Earth Troy stars.

Five Days-Di Laglang Day Diagram, L4 and L5 are located at 60 ° front and rear of the earth, respectively. | Picture source: wikipedia

The search for the Earth Troy asteroid did not stop. In 2017, Osiris-Rex in the United States and Hayabusa 2 small asteroid detectors in Japan searched the L4 and L5 areas of the earth during the flight, but unfortunately nothing was obtained. Fortunately, on December 12, 2020, ten years later, the pan-star plan in the United States discovered the second day-land L4 asteroid: 2020 XL5. This asteroid has a larger diameter and reached 1.2 kilometers. The orbit calculation shows that the asteroid was "captured" as an Earth Troy asteroid by about 500 years ago, and it will leave the current track after 4000 years.

Compared with other types of near -earth planets, the two Earth Troy asteroid threats to the earth is much smaller, and at least thousands of years do not have to worry about them hitting the earth. However, scientific asteroids have attracted much attention. This is because their unique dynamic characteristics help us to provide us with key clues to the early formation of the solar system. In addition, some scholars have noticed that because the low -income Earth Troy asteroid is very good, they can become a space base for exploring the solar system, and may even be used as the object of space resources.

The rail of the 2010 TK7 asteroid under the coordinates of the daily ground | Source: wikipedia

In summary, we noticed that the orbit of near -ground asteroids is indeed strange. The research on their track characteristics, origin and evolution of tracks helps us to better understand the dynamic environment in the formation of the solar system, and it also helps human research How to defend the near -planet that threatens the earth's security.

Reference materials:

1. https://www.minorplanetCenter.net/

2. https://academic.oup.com/mnras/article/462/4/3441/25899844

3. http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/ 31429/1/95-1108.pdf

4. https://academic.oup.com/mnras/article/446/2/ 1867/2893013

5.

6. https://astronomical.fandom.com/wiki/2020_cd3

7. http://www.astorb.com

About the Author

Hu Shoucun

Associate researcher at the Planet Science and Deep Space Exploration Laboratory of Zijin Mountain Observatory of the Chinese Academy of Sciences. Research areas: The dynamic dynamics and formation of the solar system.

Editor -in -chief: Wang Ying

Edit: Wang Kechao

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