The sci-fi blockbuster Wandering Earth II takes you to a futuristic dystopia where the impending solar crisis has plunged the world into a state of panic.

In the movie, in order to avoid being dragged by the moon's gravity, people need to install three giant planetary engines on the moon's surface to push it out of Earth's orbit. However, the planetary engines are destroyed by the AI "Moss", causing the moon to deviate from its intended orbit and is about to crash into the Earth.

Is it true that the Moon will impact the Earth? This brings us to the theory of Roche limit, which states that as small-mass objects keep approaching large-mass objects, they will be torn into pieces due to their enormous tidal forces, eventually leading to disintegration.

In the Earth-Moon system, the fluid ocean also rises and falls due to the gravitational influence of the Moon. As the Moon comes closer to the Earth, the Earth's gravity will knead and stretch the Moon more and more violently, and when this distance is less than a certain threshold value, the violent tidal force will tear the Moon into pieces - this threshold distance is the Moon's " Roche limit ", Gou Lijun said, a researcher from National Astronomical Observatories of China.

According to scientists' observations, the Moon is currently moving away from Earth at a slow pace. As early as the 1960s and 1970s, scientists measured that the Moon is moving away from Earth at a rate of about 3.8 centimeters per year, and this distance is mainly the result of the Earth's tidal forces. However, it is no surprise that the Earth and the Moon will be at peace with each other.

In order to use the planetary engine to push the Earth, the rotation of the Earth is gradually slowing down. The length of a day is set to 60 hours. Why has the length of the Earth's day become longer, and has the Earth's rotation really slowed down?

Now the Earth's day is 24 hours, because the Earth's rotation from west to east takes about 24 hours a week. In the film's setting, the Earth needs to brake, the time to completely stop rotating is set to be in 2065. According to projections, the Earth's rotation speed will take about 60 hours to rotate in a week in 2058.

The Earth's rotation has accelerated in recent years, and scientific research has found that the Earth's rotation rate has shown an accelerating trend since the middle of the year 2020. According to a British media report, researchers found that July 19, 2020 is 1.4602 milliseconds shorter. However, it is the true character of the Earth to be fast and slow at times. From a shorter time scale, the Earth's rotation rate and changes are very complex and uneven, Wang Libing said, a PHD from the University of Chinese Academy of Sciences.

But in the long term, slowing down is the general trend. If the Earth's rotation slows down, the alternation of day and night will still exist, it's only the duration of both day and night that will become longer. The climate would become more extreme in most areas. Extreme climates could lead to widespread animal migrations or extinctions and significant changes in the distribution of plants. The slowing of rotation will also have an impact on ocean currents, leading to changes in cold and warm currents, she added.

(All images via VCG.)

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