The American website “Big Think” published an opinion article by Ethan Slegel, in which he talked about the reasons for the great difference between the two sides of the moon near and far from the Earth.
In his article, the writer stated that the moon is the clearest and largest celestial body that the human eye can see in the night sky.
The moon appears to us as we see it thirty times the diameter of the planet Venus, and appears to be about a million times brighter than it, but its characteristics differ from place to place even from our limited perspective of it on Earth.
To the naked eye, these differences are in the form of bright and dark spots. If you look through a telescope, you will not only see those dark spots in the brightest parts, but you will also see hills, craters and mysterious terrain, known as the line of moving glass.
And while these features may be familiar, they all contain clues to the moon’s ancient history and can help us understand why the “face” of the moon we see isn’t the only perspective that matters.
The writer stated that there are two main features of the moon that cannot be ignored: the first is that its surface is largely covered with craters and that light-colored areas are generally more crater-filled than dark areas. Many areas include small craters within medium-sized craters within giant craters, demonstrating that the larger craters are so ancient that younger and smaller craters have formed above them.
Second, the dark regions, known as lunar seas, contain relatively few craters and most are smaller. These regions are notable because they are significantly different in color and composition than most of the lunar surface.
The writer pointed out that the same side of the Moon always faces the Earth, but different parts of the lunar hemisphere light up throughout the month depending on the relative positions of the Earth, Moon and Sun. Since the moon’s orbit is elliptical , it moves faster when it is closer to Earth and slower when it is further away, which explains the always slightly visible face of the moon, a phenomenon known as lunar wobble.
When the Soviet spacecraft Luna 3 managed to reach the far side of the moon, we got the first images. Although the image was not of high quality, it revealed that the near side of the moon is very different in terms of the number and size of the lunar craters and seas than the opposite side.
This discovery came as a huge shock, for decades, even as the image quality and our understanding of this side of the moon have improved. So what are the big differences between the near and far side of the moon?
The writer stated that the first immediately noticeable difference is the almost complete absence of lunar seas on the dark side. There is one prominent in the northern hemisphere of the moon, but it is small, and there may be some smaller ones but not seas as wide or deep as those on the near side of the moon.
The second difference is that the craters on the opposite side are more prominent and precise. And with a much larger area free of seas, there are more areas full of holes. Although this was first discovered in 1959, it took longer to get to the reason for this mystery. Subsequently, the scientists found that the previous analyzes were wrong.
The writer explained that the solar system is filled with dangerous comets and asteroids that periodically dissipate into the interior adjacent to our star. And sometimes the emergence of comets and meteors stem from these bodies. But when things go wrong, one of those large objects collides with a larger object, creating a disastrous effect. For this reason, it is possible that when these huge space rocks head towards the moon from the opposite side there is nothing blocking their path and colliding with it, but when they approach the moon from the nearest side, the Earth behaves like a shield.
It should be noted that the opposite side is filled with about 30 percent more holes than the near side, which is a huge difference.
This interpretation presents no differences in the abundance of lunar seas that appear on the near side versus the opposite side. The seas are believed to have emerged as a result of lava flows from the fissures. And it turns out the answer has to do with collisions in space, but not comets and asteroids.
About 4.5 billion years ago, when the solar system was still in its infancy, mainly Earth was formed. It was about 90 to 95 percent of its current mass. But there was another very large planet the size of Mars in an orbit roughly similar to that of Earth. For tens of millions of years, these two bodies have been orbiting precariously distant from each other. Finally, about 50 million years after the solar system was formed, they collided with each other.
The Earth eventually formed, while a large amount of debris was dispersed into space. Over time, a large amount of this debris combined with the effect of gravity and Earth’s heat to form the moon, while the rest made their way to Earth or elsewhere in the solar system. There is now evidence that moons orbiting other rocky worlds, such as Mars and Pluto, likely formed from giant impacts.
Among the hypotheses put forward – according to the author – is that it is possible that the position of the moon was much closer to us at the beginning, which indicates that it formed gradually after a very short time, that is, after about 100,000 years or less. . These latter details are currently unknown, but a strong possibility remains. If so, it is possible that Earth’s heat affected the material on both sides of the moon during its formation.
It wasn’t until 2014, 55 years after peering at the opposite side of the moon, that a study by Arpita Roy, Jason Wright and Stein Sigurdsson seemed to provide the supporting evidence. They examined the event that created the first Earth-Moon system and followed the possible paths of its physical evolution, as the Moon formed from a disk of debris orbiting the planets and the Earth. And if the Earth is too hot, it runs out of some elements as it gets closer to the Earth, such as calcium and aluminum. In other words, the heat of the early Earth creates a chemical gradient within the Moon, resulting in a different composition for the side of the Moon closest to Earth than the side furthest from Earth.
The writer added that the very strong tidal forces remind us that the Earth is very large compared to the Moon (about 70 times its mass) and that the Moon was closer to the Earth in the past. If this is the case, the greater abundance of calcium and aluminum in the farthest part of the disk surrounding the planet has produced a thicker crust on the opposite side of the moon than on the near side.
The writer pointed out that the lunar seas we see are evidence of lava flows that occurred much later, when molten rock flowed into large basins and plains on the moon’s surface. A thinner crust on the near side and a different composition on the opposite side explain why the two faces are so different even after billions of years.
Source: Arabic 21
