If the rotational speed of the Earth around the Sun and its own rotation were equal, our planet would be tidally locked. This means that one side of the planet would always face the Sun, while the other side would be perpetually covered in darkness.
To the eyes of us Earthlings, the Moon is the most observable celestial body in the night sky. If you observe the Moon closely, you will notice that at any given time, the surface of the Moon remains unchanged, which indicates that it always faces Earth with the same side.
The Moon orbits the Earth. (Illustrative image).
In fact, this phenomenon is not mysterious; the reason is that the Moon is tidally locked to the Earth, causing its orbital period around the Earth to equal its own rotation period.
Similarly, if the Earth were tidally locked to the Sun, one side of the Earth would always face the Sun, thereby making one side of the Earth perpetually in daylight while the other side would always be in darkness.
Thus, the question arises: what would happen to the Earth in this scenario? In reality, researchers have used computer models to simulate this situation.
For convenience in description, we can refer to the part of the Earth that is “always in daylight” as the “day hemisphere”, while the other part can be called the “night hemisphere.”
If the Earth were tidally locked to the Sun, one side would always be in daylight, and the other would always be dark. (Illustrative image).
Since the “day hemisphere” is constantly exposed to sunlight, its surface temperature would be higher, while the situation in the “night hemisphere” would be the opposite, leading to a significant temperature difference between the “day hemisphere” and “night hemisphere.” However, because the Earth’s atmosphere can exchange heat, this difference would not be as great as on other planets.
The simulation results indicate that the average temperature of the “day hemisphere” would be around 40 degrees Celsius, which can be described as very hot, while the average temperature of the “night hemisphere” would be about minus 40 degrees Celsius, resulting in freezing conditions on that side. Only the area at the intersection of the “day hemisphere” and “night hemisphere” would have temperatures suitable for human survival.
However, this area would be very narrow, averaging only about 60 kilometers wide. In this region, the hot air from the “day hemisphere” would compete fiercely with the cold air from the “night hemisphere,” resulting in strong, endless convective weather, essentially leading to storms and intense thunderstorms at any moment…
There would be strong, endless convective weather, essentially leading to storms and intense thunderstorms… (Illustrative image).
On the other hand, the distribution of land and sea on Earth would also undergo significant changes. The Earth is not a perfect sphere; its equatorial radius is about 6,378 kilometers, while its polar radius is about 6,357 kilometers. There is a gap of about 21 kilometers in distance.
This means that, overall, the areas near the Earth’s equator have a certain degree of bulging. Logically speaking, seawater on the Earth’s surface should flow towards areas of higher latitudes due to elevation differences. However, the reality is that there is indeed a vast ocean near the Earth’s equator due to “centrifugal force.”
According to the principle of tidal locking, if one side of the Earth is always in daylight and the other is always dark, it implies that the Earth’s orbital period around the Sun equals its own rotation period, and with such a low rotational speed, the “centrifugal force” generated would be so small that it could essentially be ignored.
In this case, seawater in the low-latitude regions of the Earth would flow into higher latitude areas, inundating vast land regions. These areas would essentially be landlocked. The land would connect to form a ring-like structure on the Earth’s surface, subsequently dividing the oceans into two large regions as a whole.
These lands would connect to form a ring-like structure on the Earth’s surface. (Illustrative image).
Moreover, the air in the Earth’s atmosphere would also experience a phenomenon similar to that of seawater, flowing towards lower latitudes in large quantities. Based on this, combined with the elevation of the land, the air in these land areas would become very thin.
Worse still, the generation of the Earth’s magnetic field is closely related to the Earth’s rotational speed. If the Earth were to complete its rotation just once a year, it would lose its strong magnetic field. Without the protection of a strong magnetic field, the natural environment of the Earth would deteriorate.
In summary, it can be observed that if one side of the Earth were always in daylight while the other side remained in perpetual darkness, the natural environment would become extremely poor, leading to the extinction of many existing species on Earth, and even humans might not be able to survive.
Fortunately, this is merely a hypothetical scenario that will not occur, as in reality, the Sun does not tidal lock the Earth.
Although the gravitational pull of the Sun does slow down the Earth’s rotation, this effect is very weak. According to scientists’ estimates, it will take at least another 50 billion years for the Sun to tidal lock the Earth.
It will take at least another 50 billion years for the Sun to tidal lock the Earth. (Illustrative image).
However, in about 5 billion years, the Sun will expand into a giant star, at which point its diameter will increase over 200 times its current diameter, causing its surface to reach or even exceed Earth’s orbit, meaning that the Earth will be engulfed by this red giant star.
