The origin of the "Oscillating Star" may be the moon? Uncover the mystery of its origin
A research team from Tsinghua University recently found that an asteroid codenamed 2016HO3, called "Oscillating Star", was likely hit and separated from the Bruno crater on the back of the moon in a cosmic collision event. This research result was recently published in the academic journal Nature Astronomy.
In the future, my country will launch the "Tianwen-2" mission, which will carry out a mission to accompany and return samples from this asteroid. Today's "Science and Technology Driving Force" will uncover the mystery of the origin of this asteroid - "Oscillating Star".
Speaking of this asteroid, it is a veritable "small" planet. How small is it? Scientists predict that its diameter is only about 50 meters. The reason why it is called "Oscillating Star" is that it has been "restlessly" oscillating. And because of its special position in space, it is also regarded as a "quasi-satellite" of the earth.
The diameter is about 46-58 meters and the revolution period around the sun is about 366 days
This near-Earth asteroid was officially announced on April 27, 2016, code-named 2016HO3 and with an international permanent number of 469219. Scientists estimate that the asteroid has a diameter of about 46-58 meters, a rotation period of about 28 minutes, and an orbital period of about 366 days around the sun.
In a special orbit, it is a "quasi-satellite" of the Earth
Scientists have discovered through observation that this asteroid is in a very peculiar orbit. It not only orbits the sun like other asteroids, but also oscillates up and down and left and right relative to the earth in a very distant orbit, hence the name "Oscillating Star". Experts say that if you look from the earth's perspective, this asteroid looks like it is orbiting the earth, but this does not mean that it is actually orbiting the earth, which is why this asteroid is considered a "quasi-satellite" of the earth, rather than a satellite.
Baoyin Hexi, Professor of the School of Aeronautics and Astronautics, Tsinghua University: It is actually at the Lagrange point between the Sun and the Earth. Of course, it does not stay at one point, but moves around the Lagrange point. So it is easy for us to think that it has some relationship with the origin of the Earth. Is it formed together with the Earth, or was it a satellite of the Earth in the past? Or was it born together with the Moon? Or is it possible that it was separated from the Moon?
Always "oscillating" on the Sun-Earth Lagrange point
The Sun-Earth Lagrange point mentioned by Professor Baoyin Hexi refers to the point where the forces exerted on the asteroid by the two major celestial bodies, the Sun and the Earth, can reach a balance. At this point, the asteroid can remain relatively still. However, the "Oscillating Star" is not a peaceful asteroid. It has been oscillating continuously for millions of years.
Where did the "Oscillating Star" come from? Why did it appear in such a strange orbit? Previously, foreign researchers have proposed that this asteroid is likely to come from the moon, but there is not enough evidence to prove it.
Through observations of the "Oscillating Star", the Tsinghua team discovered that the spectrum it reflects is very similar to that of the moon, and orbital analysis and calculations also pointed to the moon as the origin of the "Oscillating Star".
April is the best time to observe the moon when it is closest to the Earth.
Experts from the research team said that it is very difficult to study the origin of this asteroid and obtain useful information. On the one hand, although the asteroid is predicted to have a diameter of 46-58 meters, equivalent to a building with more than ten floors, objects of this size are like dust in space and are extremely difficult to discover and observe. On the other hand, it is 5.21 million kilometers away from the Earth at its closest point, and the best time to observe it is only in April every year when it comes to its closest point to the Earth.
The spectrum reflected by the "Oscillating Star" is very similar to that of the Moon
Despite the difficulties, scientists from various countries still seized the brief opportunity to study the asteroid. Spectral observation and analysis results show that the spectrum reflected by "Oscillating Star" is very similar to that of the moon, so scientists believe that this shows that the surface material of the asteroid is very close to the moon, and may even come from the moon.
Cheng Bin, a postdoctoral fellow at the School of Aeronautics and Astronautics, Tsinghua University: But we cannot determine where on the moon it came from in this way. We found that most of the fragments thrown off the lunar surface will immediately fall to the earth and become the lunar meteorites we find on earth. Only a small number of lucky ones can enter the heliocentric orbit after a long period of evolution.
Although spectral observations and related analysis and calculations cannot confirm that this asteroid came from the moon, they gave the research team a clear direction for exploration, which is to look for clues on the moon.
If Oscillating Star was once part of the moon, why did it end up in its current orbit and wander alone in the universe? The research team believes that the huge impact of the meteorite hitting the moon's surface may have ejected Oscillating Star and put it in its current orbit. As long as they can find this specific impact crater, they can determine the origin of Oscillating Star. To this end, the team developed and designed a lunar surface impact simulation model to find the key impact crater.
The best way to determine whether the "Oscillating Star" was ejected when a meteorite hit the lunar surface is to reproduce the impact. This task, which is impossible to achieve in reality, can be reproduced through supercomputer big data simulation with the advancement of science and technology. Since 2019, teachers and students in Baoyin Hexi's research group have started to develop and design a lunar surface impact simulation model.
Cheng Bin and his colleagues first calculated how large the object and how fast the impact would have to be to eject a fragment as large as Oscillating Star from the lunar surface. Then they calculated how large the crater would have been. The results showed that the impact would have left a crater with a diameter of at least 10-20 kilometers.
However, when they got the calculation results, they found that there were too many impact craters on the lunar surface that met this condition.
Cheng Bin, a postdoctoral fellow at the School of Aeronautics and Astronautics at Tsinghua University: There are a lot of impact craters that meet the constraint of 10 to 20 kilometers that we proposed, thousands or even tens of thousands of them. We are very confused about which one is the origin impact crater.
Simulation calculations found that "oscillating stars" are "young" celestial bodies
In subsequent simulations, the research team found that most of the debris produced by meteorite impacts will leave the orbit near the Earth within 10 million years after the impact, and only in very rare cases may they be preserved and eventually enter an orbit similar to that of the "Oscillating Star". This means that the age of the "Oscillating Star" should be less than about 10 million years.
The source of the age condition points to Bruno crater
The research team found that there is only one impact crater on the lunar surface that is at least 10-20 kilometers in diameter and about 10 million years old, and that is the Bruno crater on the back of the moon.
Exploring the origin of asteroids through craters is an unprecedented attempt in the field of planetary science. Through the long-term orbital evolution of lunar escape fragments, the research team clearly demonstrated how the "Oscillating Star" was born from the Bruno impact crater and finally stabilized in its current orbit after millions of years of space travel.
The full name of the Bruno crater is the Giordano Bruno crater. It is located on the back of the moon and has a diameter of about 22 kilometers. The impact simulation model made by the research team simulated this impact. About 10 million years ago in ancient times, a meteorite with a size of nearly 2 kilometers hit the moon at a speed of about 18 kilometers per second. The moment it reached the surface of the moon, the huge impact caused the meteorite to quickly disintegrate. The moon also ejected a large number of fragments in the impact. Some of these fragments fell back to the moon under the action of the moon's gravity, and some fragments flew into space with this force.
Research suggests that the "oscillating star" originated from the Bruno crater on the far side of the moon
The big data simulation not only reproduced the impact, but also restored the orbital changes of the fragments nearly tens of millions of years after they were ejected from the moon. The research team believes that this can basically confirm that the "oscillating star" originated from the moon.
Cheng Bin, a postdoctoral fellow at the School of Aeronautics and Astronautics at Tsinghua University: If this star really came from the moon, then its origin must be the Bruno crater. In addition to the constraints of size and age, there are also spectral constraints. We compared the spectral data of the Bruno crater with the spectral data of the "oscillating star" we observed and found that they are very close. This is equivalent to us verifying from three angles that the Bruno crater is the origin of the "oscillating star", and there is a very high possibility that it is.
Experts said that the research results of the School of Aeronautics and Astronautics of Tsinghua University not only gave the scientific community a new understanding of the origins of near-Earth asteroids, but also created a new method for studying the origins of asteroids.
Baoyin Hexi, professor at the School of Aeronautics and Astronautics at Tsinghua University: There will be a completely new understanding. No one has ever thought that these asteroids might have been hit by large celestial bodies. If this is verified by some actual detection data or sampling, or detection in the future, it will be a very significant development in planetary science.
Wu Weiren, chief designer of China's lunar exploration project, once revealed at the China Space Day conference that my country plans to launch the Tianwen-2 probe around 2025 to conduct companion exploration and sample return of an asteroid. The Tianwen-2 probe will explore this "oscillating star."
In the future, if Tianwen-2 can successfully retrieve samples, it will help to solve the mystery of the origin of the "Oscillating Star", which will be of great significance to our understanding of the formation of the solar system, the formation of the Earth-Moon system, and the safety of the Earth.
