Are there wandering planets in the universe? Here's everything that "The Wandering Earth 2" didn't say

The earth itself is not a hard rock. 40-70 kilometers below the crust is lava, which is somewhat similar to the structure of an egg. If you want to drive more than 10,000 engines to push the earth to "walk" for just a hundred years, the pressure exerted by the engines on the earth is something the earth cannot bear, and the shell of the "egg" will be broken. If the engines slowly accelerate and gradually reach maximum power, the earth's "wandering" time will be longer, even tens of thousands of years. During the "wandering", it is difficult to predict what will happen to the earth, what it will encounter, and what human civilization will experience.

If the solar crisis is imminent, how can humans survive? As the only planet in the Milky Way known to have life, the Earth is constantly being "burned" by the sun.

In five or six billion years, the Sun will reach the end of its life, and this "roasting" will become extremely deadly.

The recently popular movie "The Wandering Earth 2" unfolds against the backdrop of this impending doomsday. In the film, humans try to survive with the help of thousands of giant planetary engines, quantum computers that know everything, and space elevators that soar into the sky.

So, in reality, will the sun eventually deal a fatal blow to the earth? Will the earth decay along with the sun? Can planetary engines really propel the earth to "wander"? To this end, the reporter interviewed several scientific consultants, experts and scholars of "The Wandering Earth 2" to interpret the hard-core science of "The Wandering Earth".

If the sun comes to an end, can the earth survive?

The solar crisis begins to emerge, and humans join hands to meet the challenge... The future picture presented in "The Wandering Earth 2" is cruel yet inspiring.

The sun, a huge "fireball" about 150 million kilometers from the earth, is the largest celestial body in the solar system. About 4.6 billion years ago, the sun was formed by the collapse and condensation of a nebula under its own gravity, about 26,000 light-years away from the center of the Milky Way.

At present, the sun is in its prime, which is called the main sequence stage in astronomy. This stage will last about 10 billion years. It brings light and energy to the earth and is an indispensable factor for the origin of life. However, sunspots, flares and coronal mass ejections 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.

In the Milky Way, more than 90% of stars will eventually evolve into white dwarfs. At the end of their evolution, they will devour the planets in their nearby orbits. As an "ordinary" star, the sun will also end up as a white dwarf. Does this mean that the planets around the sun, including the earth, are destined to be devoured?

"If a planet is relatively close to a star, there is a high possibility that it will be swallowed by the star," Gou Lijun, scientific consultant of "The Wandering Earth 2" and researcher at the National Astronomical Observatory of the Chinese Academy of Sciences, told reporters.

However, being "swallowed" is not the only fate of planets. The sun will eventually experience a planetary nebula explosion and become a white dwarf. Around the white dwarf, the original planets may also exist.

As human observation methods improve, astronomers have indeed discovered some planets orbiting around white dwarfs.

On September 16, 2020, the international authoritative academic journal Nature published an article stating that a team of American scientists had published for the first time evidence of a Jupiter-sized planet orbiting a white dwarf. In addition, in February 2022, British astronomers discovered that there may also be a planet in the "habitable" zone near a white dwarf numbered WD1054-226, 117 light-years from Earth.

Can the Earth escape and avoid the "solar crisis"?

In 2078, the Earth will encounter a solar "helium flash" crisis, which is the key to humans' decision to "wander" in the movie.

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 is "roasted" by the sun.

"The reason why the sun shines is that nuclear reactions are taking place in the sun's core, where hydrogen is fused to form helium. This process gradually consumes hydrogen, leading 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 Science at Nanjing University, told reporters. "As the sun's core, which is mainly composed of helium, gradually shrinks, its temperature gets higher and higher. When the temperature reaches about 100 million degrees Celsius, helium will be ignited, and a large amount of helium will complete the fusion reaction within a few minutes. The energy released is huge, and the light emitted will suddenly increase by about 50 times. This process is the helium flash."

In another 5 billion years, after the sun evolves into a red giant, its surface temperature may drop from the current 5,700 degrees Celsius to about 3,000 degrees Celsius, and the hydrogen in the core of the sun will be consumed. Liang Wenjie, scientific consultant of "The Wandering Earth 2" and researcher at the Institute of Physics of the Chinese Academy of Sciences, said: "Helium flashes usually occur at the end of the evolution of red giants. In the red giant stage, the sun has expanded to the orbit of the earth, and the surface temperature reaches about 3,000 degrees Celsius, while the melting point of the earth's rocks is below 2,000 degrees Celsius. Therefore, whether it is the temperature change in the red giant stage or the sudden outbreak of helium flash, it will melt the earth."

If the Earth's survival crisis is inevitable in more than 5 billion years, is it possible to avoid the Sun's edge in advance during its "expansion period", change its orbit and find another place, and then return to the Earth's original orbit after the helium flash and other crises are resolved?

Liang Wenjie believes that even if the Earth returns to its original orbit after the solar crisis is resolved, it may not be of much significance to the Earth, "because the Sun will have entered its aging period by then, and the heat it provides should not be able to sustain life on Earth. Jupiter, Saturn, Uranus, and Neptune in the solar system are all frozen planets because they are far away from the Sun, with planetary temperatures of minus 100 to 200 degrees Celsius. If the Earth still wants to return to the Sun to obtain energy, it will have to constantly correct its orbit and get closer to the Sun, but eventually the 'big fireball' of the Sun will still 'go out'."

"Even if it is feasible to 'run away from home' temporarily and then return home, the Earth needs to accelerate to leave its original orbit and then slow down. The speed adjustment process will be very long and will consume huge energy on the Earth. It is a huge project. What's more, there are risks in returning to the Earth's current orbit and approaching the sun," said Liang Wenjie.

If we give up the sun and look for other stars, we will also face greater challenges. Gou Lijun believes that if the earth chooses another cosmic "habitat" and chooses a new star to orbit, it means that it will have to "adapt" to a new planetary orbit, and the speed, direction, energy, etc. of entering the orbit need to be accurately calculated. The existing technology of mankind is unlikely to achieve the entry of planetary bodies into orbit in the short term.

Would nuclear fusion be a better "wandering" solution?

In the film, humans try to find a way to survive when the end of the world comes through the Mountain Moving Plan, Ark Plan, Moon-by-Moon Plan, and Digital Life Plan. In the end, tens of thousands of huge planetary engines become the hope to propel the earth to embark on a "wandering journey".

Liang Wenjie provided advice on the planetary engines, lunar engines, the physical effects of the moon-by-moon plan, and the way the moon explodes. He said: "From an artistic point of view, the way the earth 'wanders' in the film is a great imagination, but it is difficult to achieve from the current scientific level."

Liang Wenjie explained: "The earth itself is not a solid rock. 40-70 kilometers below the crust is molten rock, which is a bit like the structure of an egg. If you want to drive more than 10,000 engines to push the earth to 'walk' for just a hundred years, the pressure exerted by the engines on the earth is something the earth cannot bear and will break the shell of the 'egg'. If the engines slowly accelerate and gradually reach maximum power, the earth's 'wandering' time will be longer, even tens of thousands of years. During this 'wandering' period, what will happen to the earth, what will happen to it, and what human civilization will experience, it is difficult to predict."

"But if we 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 to make two atomic nuclei collide with each other under high temperature, and finally combine to generate a new atomic nucleus, which can release huge energy. The key is to output the energy generated by nuclear fusion stably for a long time, continuously and stably. To achieve this, many technical problems need to be overcome.

However, even if hydrogen nuclear fusion can eventually be achieved and can provide a large amount of energy for humans, the important raw materials for nuclear fusion, deuterium and tritium, are relatively low in abundance in the earth's seawater, and the reserves of helium-3, a raw material for nuclear fusion, are 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 propel 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 materials to obtain nuclear energy. Compared with light nuclear fusion using deuterium, tritium, and helium-3 as raw materials, the efficiency of heavy nuclear fusion in obtaining fusion energy is very low. Although silicon and oxygen elements account for a large proportion of 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 may even reach billions of degrees Celsius, which greatly challenges the current scientific and technological capabilities of mankind.

Are there rogue planets in the universe?

If one day the Earth has to embark on a "wandering" journey, will it be able to encounter celestial bodies with the same suffering in the vast universe?

Gou Lijun, scientific consultant of "The Wandering Earth 2" and researcher at the National Astronomical Observatory of the Chinese Academy of Sciences, said that in the universe, there is a type of planet that does not orbit any star, namely rogue planets. At present, humans have detected about 100 rogue planets, the larger ones are about ten times the size of Jupiter, and the smaller ones are close to the Earth.

"According to our current understanding, there are two possible ways that rogue planets are formed: one is that there are only planets themselves when they are formed. The other possibility is that the planet is 'ejected' from the star system." Gou Lijun gave an example. If a larger star is near the solar system, it is possible that the outermost planet in the solar system will deviate from its original orbit under the influence of gravity and eventually leave the solar system.

Liang Wenjie, the scientific consultant of The Wandering Earth 2 and a researcher at the Institute of Physics of the Chinese Academy of Sciences, offered another hypothesis: large stars will experience a violent explosion at the end of their evolution, namely a supernova explosion, and eject a large amount of interstellar matter. "Planets near the star may be thrown out of their original orbits at this time and become wandering planets."

In recent years, with the improvement of observation technology, rogue planets have been discovered continuously. In August 2018, American scientists confirmed that a planet with a mass about 12 times that of Jupiter was wandering alone about 20 light years away from the Earth, not attached to any star. It was the first rogue planet discovered using a radio telescope.

In 2020, American and Polish astronomers wrote in the Astrophysical Journal Letters that with the help of microlensing, they may have discovered the smallest rogue planet known to date, whose "weight" is about 10% of the Earth.

"Rogue planets do not emit light, so they are difficult to detect. They are often discovered due to an accidental event, so the time they are noticed by the detector is very short. This also leads to the current limited research on rogue planets." Gou Lijun said that based on the current level of human technology, it is impossible to determine whether there is life on rogue planets.

Liang Wenjie analyzed that the existence of life requires not only the elements that constitute life, such as amino acids, carbon, hydrogen and other substances, but also suitable temperatures. "The evolution of the universe sometimes ejects some organic matter onto stars, and organic matter needs suitable temperatures to survive. Wandering planets do not generate heat, and there are no stars to provide them with heat, so they will continue to cool down until they reach the lowest temperature in the universe. Such low temperatures make it difficult for life to grow," Liang Wenjie said.

Source: Science and Technology Daily, Inner Mongolia Association for Science and Technology's "Cloud Science Popularization" APP

Editor: Qiao Yuxin

Reviewer: Naren Na Zhao Lewen