The earth itself is not a hard rock, 40-70 kilometers below the earth’s crust is lava, which is somewhat similar to the structure of an egg. If you want to drive more than 10,000 engines, it will take only a hundred years to push the earth to "walk", and the engine will put pressure on the earth, which the earth cannot afford, and will break the shell of the "egg". And if the engine slowly accelerates and gradually reaches maximum power, the earth will be "wandering" for a longer time, or even thousands of years. During the "wandering" period, it is difficult to predict what will happen to the earth, what will happen to it, and what human civilization will experience.
If the solar crisis is imminent, how can human beings survive? As the only planet known to exist in the Milky Way, the earth is always "roasted" by the sun.
In five or six billion years, the sun is nearing the "end" of its life, and this "roasting" will become extremely deadly.
The recent blockbuster film "The Wandering Earth 2" unfolds against this backdrop of impending doom. In the film, humans try to find a chance to survive with the help of 10,000 giant planetary engines, quantum computers that understand everything, and towering space elevators.
So, in reality, will the sun eventually deal a fatal blow to the earth? Will the earth decline with the sun? Can planetary engines really push the earth to "wander"? To this end, the Science and Technology Daily reporter interviewed a number of scientific consultants, experts and scholars of "Wandering Earth 2" to interpret the hard core science about "Wandering Earth".
If the sun comes to an end, will the earth be spared?
The sun crisis had just appeared, and humans had joined hands to face it… The future depicted in "The Wandering Earth 2" was cruel but exciting.
The sun, a huge "fireball" about 150 million kilometers from the earth, is the largest celestial body in the solar system. About 4.60 billion years ago, about 26,000 light-years from the center of the Milky Way, the sun was formed by the collapse of a nebula under the influence of its own attractive force.
At present, the sun is in its prime, astronomically known as the main sequence stage, which lasts about 10 billion years. It brings light and energy to the earth, and is an essential factor in the origin of life. But sunspots, flares, and coronal mass ejections also often cause damage to human production and life.
However, the sun will eventually age, and the origin of "The Wandering Earth 2" is the rapid expansion and aging of the sun.
More than 90 per cent of stars in the Milky Way eventually become white dwarfs. At the end of their evolution, they devour nearby planets. As an "ordinary" star, the Sun also ends up as a white dwarf. Does this mean that the planets around the Sun, including the Earth, are destined to be devoured as well?
"If the planet is relatively close to the star, it is very likely to be swallowed by the star," Gou Lijun, a scientific advisor to The Wandering Earth 2 and a researcher at the National Astronomical Observatory of the Chinese Academy of Sciences, told Science and Technology Daily.
However, "being swallowed" is not the only destination for a planet. The sun will eventually experience an outburst of a planetary nebula and become a white dwarf. Around the white dwarf, the original planets may also exist.
With the improvement of human observation methods, astronomers have indeed discovered some planets orbiting white dwarfs around them.
On September 16, 2020, the international authoritative academic journal Nature published an article saying that a team of American scientists had for the first time published evidence of a Jupiter-sized planet orbiting a white dwarf. In addition, in February 2022, British astronomers discovered that a planet may also exist in the "habitable" zone near a white dwarf named WD1054-226, 117 light-years away from Earth.
Can the earth escape and avoid the "solar crisis"?
In 2078, the earth will encounter the "helium flash" crisis of the sun, which is the key to the human decision to "wander" in the movie.
The helium flash is a key link in the evolution of the sun, and it is also the moment of life and death when the earth accepts the sun’s "roast".
"The sun shines because the core of the sun is undergoing a nuclear reaction, where hydrogen is fused to form helium. This process will gradually consume hydrogen, which will then lead to the collapse of the sun’s core. At the same time, the envelope outside the sun’s core expands under high pressure." Chen Pengfei, a professor at the School of Astronomy and Space Sciences at Nanjing University, told reporters. "When the core of the sun, which is mainly composed of helium, gradually contracts, its temperature is also getting higher and higher. When the temperature reaches about 100 million degrees Celsius, the helium will be ignited, and a large amount of helium will complete the fusion reaction in a few minutes. The energy released is huge, and the light emitted will suddenly increase by about 50 times. This process is helium flash."
In more than five billion years, after the sun becomes a red giant, its surface temperature may drop from more than 5,700 degrees Celsius now to about 3,000 degrees Celsius, when the hydrogen in the sun’s core will be exhausted. "Helium flashes usually occur at the end of the evolution of red giants," said Liang Wenjie, a scientific consultant for Wandering Earth 2 and a researcher at the Institute of Physics of the Chinese Academy of Sciences. "In the red giant stage, the sun has expanded to Earth’s orbit, and the surface temperature reaches about 3,000 degrees Celsius, while the melting temperature of the earth’s rocks is below 2,000 degrees Celsius. Therefore, whether it is a temperature change in the red giant stage or a sudden explosion of helium flashes, the earth will melt."
If the survival crisis of the earth is inevitable in more than 5 billion years, can it be avoided in advance during the "expansion period" of the sun, change the orbit and find another place, and return to the original earth orbit after the helium flash and other crises are lifted?
Liang Wenjie believes that even if the solar crisis is lifted and the earth returns to its original orbit, it may not be of much significance to the earth, "because the sun has entered the aging period at that time, and the heat it provides should not be able to support the survival of life on earth. Jupiter, Saturn, Uranus, and Neptune in the solar system are all frozen planets due to their distance from the sun, and the temperature of the planet is minus one or two hundred degrees Celsius. If the earth wants to return to the sun to obtain energy, it will have to constantly correct its orbit and approach the sun, but in the end the’big fireball ‘of the sun will still be’extinguished’."
"Even if it is possible to temporarily’run away from home ‘and then return home, the earth needs to accelerate out of the original orbit and then slow down. The process of adjusting the speed will be very long, and it will consume huge energy on the earth, and the project will be huge. What’s more, the process of returning to the earth’s current orbit and approaching the sun also has risks," Liang Wenjie said.
And if you give up the sun and find other stars, you will also face greater challenges. Gou Lijun believes that if the earth chooses another "habitat" in the universe and chooses a new star to orbit, it means to "adapt" to a new planetary orbit. Then the speed, direction, energy, etc. of entering the orbit need to be accurately measured, and it is difficult for human existing technology to achieve planetary celestial bodies in the short term.
Would nuclear fusion be a better "wandering" solution?
In the film, humans tried to find life at the end of the world through the Mountain Moving Project, the Ark Project, the Monthly Project, and the Digital Life Project. In the end, tens of thousands of giant planetary engines became the hope to push the earth to start a "wandering journey".
Mr. Liang, who has advised on the film’s planetary and lunar engines, the physics of the month-by-month plan and the way the moon explodes, said: "Artistically, the’wandering ‘way of the earth in the film is a great imagination, but it is still difficult to achieve at the current level of science."
Liang Wenjie explained: "The earth itself is not a hard rock, 40-70 kilometers below the earth’s crust is lava, which is a bit similar to the structure of an egg. If you want to drive more than 10,000 engines, and it only takes a hundred years to push the earth to’walk ‘, the engine will put pressure on the earth, which is beyond the earth’s ability to bear, and will break the shell of the’egg’. And if the engine accelerates slowly and gradually reaches maximum power, the earth will be’wandering ‘for a longer time, even thousands of years. During the’wandering’ period, it is difficult to predict what will happen to the earth, what will happen to it, and what human civilization will experience."
"But if you consider the energy supply method, controlled nuclear fusion is worth looking forward to, although it still faces great technical challenges." Liang Wenjie introduced that nuclear fusion is in the case of high temperature, two atomic nuclei collide with each other, and eventually combine to form a new atomic nucleus, which can release huge energy. The key to this is to continuously export the energy produced by nuclear fusion for a long time. To achieve this, many technical problems need to be overcome.
However, even if the nuclear fusion of hydrogen could eventually be realized and provide a large amount of energy for humanity, the important raw materials for nuclear fusion, deuterium and tritium, were in low abundance in the earth’s seawater, and the reserves of helium-3, the raw material for nuclear fusion, were also extremely scarce. Therefore, based on the total amount of resources currently available to humans, the energy of nuclear fusion is still not enough to push the earth out of the solar system.
So, is it possible to "burn stones" like in "The Wandering Earth 2" and obtain energy through heavy nuclear fusion? Liang Wenjie said that heavy nuclear fusion refers to the use of heavier elements such as silicon and oxygen as fusion raw materials to obtain nuclear energy. Compared with light nuclear fusion using deuterium, tritium, and helium-3 as raw materials, heavy nuclear fusion is very inefficient in obtaining fusion energy. Although silicon and oxygen elements have a large proportion in the earth’s crust, in order to overcome the huge electrostatic repulsion between the nuclei of heavy elements and make them produce nuclear fusion reactions, higher temperatures and stronger pressures are required, and the reaction temperature even needs to reach billions of degrees Celsius, which greatly challenges the current scientific and technological capabilities of mankind.
extended reading
Are there wandering planets in the universe?
If one day, the earth had to embark on a "wandering" journey, would it be possible to encounter celestial bodies that "sympathize with each other" in the vast universe?
According to Gou Lijun, a scientific advisor of "Wandering Earth 2" and a researcher at the National Astronomical Observatory of the Chinese Academy of Sciences, there is a type of planet that does not orbit any star in the universe, namely the wandering planet. At present, humans have detected about 100 wandering planets, the larger ones are about ten times the size of Jupiter, and the smaller ones are close to the earth.
"According to the current understanding, there may be two ways for stray planets to form: one is that when they form, only the planets themselves. Another possibility is that the planet is’ejected ‘from the star system." For example, if a larger star is near the solar system, it is possible that under the action of attractive forces, the outermost planet of the solar system may deviate from its original orbit and eventually leave the solar system.
Liang Wenjie, a science adviser for "The Wandering Earth 2" and a researcher at the Institute of Physics of the Chinese Academy of Sciences, offered another hypothesis: Large stars experience a violent explosion at the end of their evolution, a supernova explosion, and eject a large amount of interstellar material. "Planets near the star may be ejected from their original orbits at this time and become wandering planets."
In recent years, with the improvement of observation technology, stray planets have been continuously discovered by humans. In August 2018, American scientists confirmed that a planet about 12 times the mass of Jupiter was wandering alone about 20 light-years away from the earth and was not attached to any star. It was the first stray planet discovered by radio telescopes.
In 2020, American and Polish astronomers wrote in the Astrophysical Journal Letters that they might have discovered the smallest known rogue planet, with a microscopic attractive force lens, that "weighs" about 10 percent of Earth.
"Wandering planets do not emit light, so it is difficult to detect them. They are often discovered due to an accidental event, so they are paid attention to by the detector for a very short time, which also leads to the current research on wandering planets is very limited." According to Gou Lijun, according to the current level of human technology, it is impossible to determine whether there is life on wandering planets.
Liang Wenjie analyzed that in addition to the elements that make up life, such as amino acids, carbon, hydrogen and other substances, the existence of life also requires a suitable temperature. "The evolution of the universe sometimes ejects some organic matter onto the star, and the survival of organic matter requires a suitable temperature. Wandering planets do not heat up, and there are no stars to provide heat for them, so they will continue to cool down until they reach the lowest temperature in the universe. Such low temperatures are difficult to breed life," Liang Wenjie said.
