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When the Chang’e-4 mission landed in Von Karman crater on January 3, 2019, China became the first and only country to land on the far side of the Moon – the side that always faces away from Earth.
Now, China is sending yet another mission to the other side and, this time, its objective is to return the first samples from the “far side” of the Moon to Earth.
O Chang’e-6 mission, launched Fridayis expected to spend 53 days exploring the South Pole-Aitken basin to study its geology and topography, as well as collect samples from different points in the crater.
The South Pole-Aitken basin is believed to be the largest and oldest crater on the moon, spanning nearly a quarter of the lunar surface with a diameter of approximately 2,500 kilometers (1,550 miles). The impact crater is more than 8 kilometers deep.
Scientists hope that sending samples to Earth will help answer lingering questions about the intriguing far side, which has not been studied as deeply as the near side, as well as confirm the origin of the Moon.
“The far side of the Moon is very different from the near side,” said Li Chunlai, deputy chief designer at the China National Space Administration. “The extreme is basically ancient lunar crust and highlands, so there are a lot of scientific questions to be answered there.”
No real ‘dark side’
During a NASA budget hearing on April 17, Congressman David Trone asked NASA Administrator Bill Nelson why China was sending a mission to the “backside” of the Moon.
“They will have a lander on the other side of the Moon, which is the side that is always dark,” Nelson replied. “We’re not planning to go there.”
The Far Side of the Moon is sometimes called the “Dark Side of the Moon,” largely in reference to Pink Floyd’s 1973 album of the same name.
But the phrase is a bit of a misnomer for a few reasons, according to experts.
Although the far side of the moon may appear dark from our perspective, it experiences a lunar day and lunar night just like the near side and receives plenty of illumination. A lunar day lasts just over 29 days, while the lunar night lasts about two weeks, according to NASA.
The same side always faces the Earth because the Moon takes the same time to complete one orbit as the Earth and to rotate around its axis: about 27 days.
Additionally, the far side of the Moon has been more difficult to study, which has led to the nickname “dark side” and created an air of mystery.
“Humans always want to know what’s on the other side of the mountain and the part you can’t see, so this is kind of a psychological motivation,” said Renu Malhotra, Louise Foucar Marshall Professor of Science Research and Regents Professor of Planetary Sciences . at the University of Arizona in Tucson. “Of course we have sent space probes that have orbited the Moon and we have images, so in some ways it is less mysterious than before.”
Several spacecraft, including NASA’s Lunar Reconnaissance Orbiter, which constantly circles and takes images of the lunar surface, have helped shed light on the moon.
Yutu-2, a lunar rover launched by Chang’e-4 in 2019, also explored loose deposits of pulverized rock and dust scattered across the floor of Von Karman crater, located in the largest South Pole-Aitken basin.
But returning samples to Earth would allow newer, more sensitive technology to analyze lunar rocks and dust, potentially revealing how the Moon came to be and why its far side is so different from the near side.
Mysteries on the other side
Despite years of orbital data and samples collected during six of the Apollo missions, scientists are still trying to answer important questions about the Moon.
“The reason the far side is so attractive is because it is very different from the side of the Moon that we see, the near side,” said Noah Petro, NASA project scientist for both the Lunar Reconnaissance Orbiter and Artemis III, a mission that aims to take humans to the Moon for the first time since 1972. “For all of human history, humans have been able to look up and see the same surface, the same side of the moon.”
But in 1959, the Soviet Union sent a probe to fly by the far side of the Moon and captured humanity’s first images of it.
“We saw this hemisphere completely different: not covered by large volcanic lava flows, marked by craters, a thicker crust. It just tells a different story than the one next door,” Petro said.
Returning samples with robotic missions and landing humans near the transition between the two lunar regions at the south pole through the Artemis program “will help tell this fuller story of lunar history that we are missing right now,” he said.
While scientists understand why one side of the Moon always faces Earth, they don’t know why that particular side permanently faces our planet. But it could have something to do with the moon being asymmetrical, Malhotra said.
“There is some asymmetry between the side facing us and the other side,” she said. “What exactly caused these asymmetries? What are these asymmetries really? We have little understanding of this. That’s a big scientific question.”
The orbital data also revealed that the nearer side has a thinner crust and more volcanic deposits, but answers to why have eluded researchers, said Brett Denevi, a planetary geologist at Johns Hopkins University’s Applied Physics Laboratory.
“It has a different kind of geochemical composition with some strange elements that produce extra heat. There are many models that explain why the near side is different from the far side, but we don’t have the data yet,” Denevi said. “So going to the other side, getting samples and doing different types of geophysical measurements is really important to uncovering this very ancient mystery.”
Chang’e-6 is just one mission heading to the far side of the Moon, as NASA has plans to send robotic missions there as well.
Denevi helped design a mission concept for a lunar rover called Resistance, which will undertake a long trip through the South Pole-Aitken basin to collect data and samples before delivering them to Artemis landing sites near the lunar south pole. Then, astronauts will be able to study the samples and determine which ones to return to Earth.
Cracking the lunar code
One of the most fundamental questions scientists have tried to answer is how the moon formed. The prevailing theory is that some kind of object had an impact with Earth early in its history, and a giant chunk that flew off our planet formed the moon.
Scientists also want to know how the moon’s original crust formed.
Volcanic flows have created dark spots on the Moon, while the lighter parts of the surface represent the Moon’s primordial crust.
“We think that at one point the Moon was totally molten, and it was an ocean of magma, and as it solidified, the minerals floated to the top of this ocean, and that’s the lightest terrain we can see today,” Denevi said. . “Getting to the large expanses of untouched terrain on the other side is just one of the goals.”
Meanwhile, studying impact craters scattered across the lunar surface provides a story of how things moved during the early days of the solar system, at a critical point when life was beginning to form on Earth, Denevi said.
“As impacts were happening on the Moon, impacts were happening on Earth at the same time,” Petro said. “And so, whenever we look at these ancient events on the Moon, we also learn a little bit about what’s happening on Earth.”
Visiting the South Pole-Aitken basin could be the beginning of solving a multitude of lunar mysteries, Malhotra said. Although researchers believe they have an idea of when the crater formed, perhaps between 4.3 billion and 4.4 billion years ago, collecting rock samples could provide a definitive age.
“Many scientists are sure that if we figure out how old this depression is,” she said, “we will unlock all kinds of mysteries about the history of the Moon.”
CNN’s Wayne Chang contributed to this report.
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