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When the Chang’e-4 mission landed in the 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 faces the universe always.
Now, China is sending another mission to the far side, and this time, its goal is to bring back to Earth the first samples of the “hidden side” of the moon.
The Chang’e-6 mission, launched on Friday, is to spend 53 days exploring the South Pole-Aitken basin to study its geology and topography as well as collect samples from various spots around the crater.
The South Pole-Aitken basin is believed to be the largest and oldest crater on the moon, comprising nearly a quarter of the moon’s surface with a diameter of about 1,550 miles (2,500 kilometers). The impact crater is more than 5 miles (8 kilometers) deep.
Scientists hope that returning samples to Earth will help answer lingering questions about the fascinating far side, which have not been studied as deeply as the far side, as well as confirm the origin of the moon.
“The far side of the moon is very different from the other side,” said Li Chunlai, deputy chief designer at the China National Space Administration. “The distance is essentially an ancient lunar crust and highlands, so there are a lot of scientific questions to answer there.”
There is no real ‘dark side’
During the 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’ll have a lander on the far side of the moon, that’s the side that’s always dark,” Nelson replied. “We don’t plan to go there.”
The hidden side of the moon is sometimes referred to as 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 looks dark from our perspective, the near side is exactly the same on a lunar day and lunar night, and receives a lot of illumination. A lunar day lasts just over 29 days, and the lunar night lasts for about two weeks, according to NASA.
The same side always faces the Earth because the moon takes the same amount of time to complete the Earth’s orbit and rotate around its axis: about 27 days.
In addition, the far side of the moon was more difficult to study, giving rise to the nickname “dark side” and creating an air of mystery.
“People always want to know what’s on the other side of the mountain and the part you can’t see, so that’s a kind of psychological motivation,” said Renu Malhotra, Louise Foucar Marshall Research Professor of Science and Professor Regents in Planetary Sciences. at the University of Arizona in Tucson. “Of course, we’ve sent space probes that have orbited the moon, and we have images, so in a sense, it’s less mysterious than it was 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 littering the floor of Von Karman crater, which is located within the larger South Pole-Aitken basin.
But returning samples to Earth would enable the latest and most sensitive technology to analyze lunar rocks and dust, which could reveal how the moon came to be and why its side is in far as different from the near side.
Mysteries beyond
Despite years of orbital data and samples collected during six Apollo missions, scientists are still trying to answer key questions about the moon.
“The reason the far side is so strong is that it’s so different than the side of the moon that we see, the near side,” said Noah Petro, NASA’s project scientist for the Lunar Reconnaissance Orbiter and Artemis III, a mission that It aims to land humans on the moon for the first time since 1972. “Throughout human history, humans have been able to look up and see and see the same surface, the same side of the moon. “
But in 1959 the Soviet Union sent a probe to fly past the far side of the moon and took humanity’s first images of it.
“We saw this hemisphere completely different: not covered by large volcanic lava flows, marked with craters, thicker crust. It tells a different story than the other side,” said Petro.
By bringing back samples with robotic missions, and landing humans near the transition between the two lunar regions at the south pole through the Artemis program, “it will help tell this more complete story of the history of the moon that is we currently lack,” he said.
Although scientists understand why one side of the moon always faces Earth, they do not 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 in front of us and the other side,” she said. “What exactly caused those asymmetries? What are these asymmetries really? We have little understanding of that. That’s a huge scientific question.”
Orbital data has also shown a thinner crust and more volcanic deposits on the near side, but answers to why haven’t given researchers, said Brett Denevi, a planetary geologist at the Johns Hopkins University Applied Physics Laboratory.
“It has a different geochemical composition and some extra strange heat-producing elements. There are many models as to why the near side is different than the far side, but we don’t have the details yet,” said Denevi. “So it’s really important to go to the other side, get samples and do different kinds of geophysical measurements to find the long-standing mystery.”
Chang’e-6 is only one mission that goes to the edge 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 Endurance, which will take a long drive across the South Pole-Aitken basin to collect data and samples before delivering them to the Artemis landing sites near the moon’s south pole. Then, astronauts can study the samples and decide which ones to return to Earth.
Crack the moon code
One of the most fundamental questions that scientists have tried to answer is how the moon was formed. The prevailing theory is that some kind of object impacted the Earth early in its history, and a huge chunk that ejected from our planet formed the moon.
Scientists also want to know how the original crust of the moon was formed.
Volcanic flows created dark patches on the moon, while the lighter parts of the surface represent the moon’s primordial crust.
“We think at one point the moon was completely molten, and it was this magma ocean, and as that solidified, minerals floated to the top of this ocean, and that’s that lighter terrain which can be seen today,” said Denevi. “It’s just one of the goals to achieve on the vast expanses of fantastic terrain beyond.”
Meanwhile, studying impact craters littering the moon’s surface provides a history of how things moved around during the early days of the solar system at a critical point when life was beginning on Earth, Denevi said.
“As impacts were occurring on the moon, impacts were occurring on Earth at the same time,” Petro said. “And so when we look at these ancient events on the moon, we’re learning a little bit about what’s happening on Earth as well.”
A visit to the South Pole-Aitken basin could be the start of solving many lunar mysteries, Malhotra said. Although researchers believe they have an idea of when the crater was formed, perhaps 4.3 billion to 4.4 billion years ago, collecting rock samples could provide a definitive age.
“Many scientists are convinced that if we understand the age of that depression,” she said, “it will unlock all kinds of mysteries about the history of the moon.”
CNN’s Wayne Chang contributed to this report.
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