Every day, when the sun slowly rises from the east and then sinks below the western horizon, we seem to witness a natural knowledge learned from an early age. This phenomenon highlights the Earth's steady west-to-east rotation. Yet, if one looks down upon the entire solar system and sees the eight major planets orbiting the central star, you may take comfort in this strictly maintained cosmic order. Despite this order appearing fragile, as if it could collapse between one's fingers.

Although each planet is unique, their orbital direction around the same star is unified, consistent with the direction of the Sun's rotation, and so is the rotation of most planets. However, Venus seems to challenge the norm, distinguishing itself with its unusual direction of rotation.

On Venus, the scenario where the sun rises from the west could become a reality. This planet, hailed as Earth's "twin brother" due to its similar mass, volume, density, and composition, actually differs from Earth as much as heaven is from earth. This "neighbor" with extreme characteristics will bring many surprises to humanity.

Magellan probe radar data once showed that Venus's surface is covered with mountains and thousands of volcanoes, along with lava rivers stretching for 5,000 kilometers. Nonetheless, Venus's surface is in fact composed of vast plains, which at least sound like an excellent destination for space exploration.

However, the plains on Venus under extreme conditions are hardly habitable for humans. On the surface of Venus, one would face atmospheric pressure 95 times greater than at sea level on Earth, equivalent to the pressure about 1000 meters under the sea, and the air is extremely viscous. Trying to swing your arms on Venus might feel like moving through water.

Furthermore, Venus's thick layer of greenhouse gases brilliantly retains the heat from the sun, keeping its surface temperature around a scorching 480 degrees Celsius, even hotter than Mercury, which is closer to the Sun. This is caused by an uncontrolled greenhouse effect, making Venus the hottest planet in the solar system. Coupled with Venus's slow rotation speed, opposite to Earth's, one day on Venus equals 243 Earth days and nights.

Even more fascinating is that Venus's orbital period is approximately only 225 Earth days. This discovery subverts our intuition, astonishing us that the duration of a day-night cycle on Venus (one day) actually exceeds the time it takes for Venus to orbit the Sun (one year). This also explains why on Venus, the sun rises from the west. Venus's unique retrograde rotation and slow rotational speed have long perplexed astronomers, like the thick atmosphere surrounding Venus, it is filled with the unknown and mysterious.

Logically, when Venus originated from the same rotating protoplanetary disk as Earth and the other planets, it should have inherited a similar angular momentum, and its rotation direction should have been consistent with the other planets. Now, some scientists propose that the atmosphere may have played a non-negligible role in reversing the direction of Venus's rotation. Often, we may simply consider the atmosphere to be a thin layer of gas that is separate from the crust and located above the surface of the planet, and that its interaction with the solid part of the planet is minimal. However, Venus's thick atmosphere indicates that it is an integral part of the planet, omnipresent, with far-reaching influences, and is very likely to have changed Venus's own rotation behavior.

The atmosphere of Venus can completely orbit the planet in just 4 Earth days, compared to Venus's own 243 Earth-day rotational period. Such high-speed storms might exert tremendous forces on the surface of Venus. Based on this phenomenon, some scientists suggest that Venus might have originally had a prograde rotation like most planets, but at some point, its rotational axis flipped by 180 degrees. Intense atmospheric tidal forces might be the main factor causing this flip and could continue to influence Venus's rotation.

The currently most accepted explanation involves interplanetary collision. Although the present solar system seems relatively stable, the early solar system was chaotic. During a period filled with planetary collisions and competition for survival space, many planets might have been destroyed, turned into space debris, or knocked out of the solar system by larger celestial bodies. In this chaos, Venus (and Uranus) may have experienced a significant collision event that permanently altered its rotational direction.

However, earlier this year, a new study published in the journal "Cosmos" offered another viewpoint. This study took into account a unique feature of Venus—it lacks a moon, unlike other planets apart from Mercury. Scientists speculate that in the distant past, Venus might have captured and then destroyed a moon. At the beginning of the solar system's formation, thousands of planets moved along their complex orbits within the protoplanetary disk. From this dynamic and chaotic state, the construction of the planetary system became akin to a game of chance. Through computer simulations, researchers found that direct impacts between planets in such a high-density cluster were actually less common than close flybys. Therefore, based on the fact that both Venus and Mercury lack moons, they inferred that the sun's immense gravity is the primary reason these two planets do not have moons. Assuming Venus did have a moon early on and that Venus's rotation was once consistent with other planets, the moon's ultimate fate could have been retrograde.

Just as the Moon affects Earth, a hypothetical moon in orbit around Venus would have continuously influenced its rotation speed and potentially even reversed Venus's rotation direction. This hypothesized celestial body, by colliding with other nearby objects, would gradually eliminate other small moons in Venus's orbit, slowing down and eventually falling onto Venus's surface.

The satellite capture theory offers a possible explanation for Venus's unique rotational direction, slow rotation speed, and lack of natural satellites. Nonetheless, some scientists believe this theory is very difficult to prove since it would be nearly impossible to test it even with geochemical data from Venus in the coming decades. Regardless of the outcome, researchers remain keenly interested in studying Venus.

Venus and Earth, although similar in many ways, have followed distinctly different developmental paths. Venus is akin to a demonic mirror, helping us to uncover some profound truths about Earth. The habitability of Earth stands in stark contrast to Venus, which seems more like a planet intent on destroying all forms of life. Venus's uniqueness makes it a focal point of scientific investigation.

Furthermore, the dense greenhouse gas atmosphere of Venus makes it a laboratory for climate change research, an observation post for extreme weather, and possibly even a cautionary example of the tragic end that might await Earth in the future.