By Hou Weili
Humans around the world have been sharing common aspirations to learn about the mysterious moon throughout history. In Greek mythology, Selene was the goddess of the moon, reputed to drive a chariot across heaven. And in Chinese legends, lunar goddess Chang’e lives in the moon palace.
Alongside extensive literary expressions, humanity has been conducting scientific research on the celestial body, but most results have been restricted to explorations of the visible side of the moon, the side that can be seen from Earth.
With 2019 New Year festivities in the air, China rejuvenated the ambience on January 3 as its spacecraft Chang’e-4 became the first ever to land on the far side of the moon.
The mission started about 20 days ago when the Chang’e-4 lunar probe was launched from Xichang Satellite Launch Center in southwestern China. On January 3, developers decided to end its orbiting and made it touch down on the target destination: South Pole-Aitken (SPA) Basin, the largest, deepest and oldest crater in the solar system.
At 10:15 a.m., a variable thrust engine was ignited with the assistance of relay satellite Queqiao, or Magpie Bridge, operating in the halo orbit around the second Lagrangian point of the Earth-moon system, about 65,000 kilometers from the moon, where it can see both the far side of Earth and the moon.
Eleven minutes later, the probe made a soft landing at 177.6 degrees east longitude and 45.5 degrees south latitude in the Von Karman Crater in the SPA Basin. Then, rover Yutu-2, or Jade Rabbit-2 named after the pet of goddess Chang’e, drove onto the lunar surface to collect data and take photos.
On January 11, the China National Space Administration dubbed the Chang’e-4 mission a complete success after ground control received images and data.
“This is an important milestone for Chinese space exploration,” declared Wu Weiren, chief designer of China’s lunar exploration program.
Rather than loud criticism, China received unanimous applause from the international community for this endeavor. Observers referred the success as an epic feat that will go down in history.
“Congratulations to China’s Chang’e-4 team for what appears to be a successful landing on the far side of the moon,” wrote NASA Administrator Jim Bridenstine on his personal social media page. “This is a first for humanity and an impressive accomplishment.”
In fact, the mission has been about international partnerships from the beginning. The four scientific payloads used in the Chang’e-4 mission were developed by scientists from the Netherlands, Germany, Sweden and Saudi Arabia.
Johan Koehler, head of Solar System Science and Space Situational Awareness of Swedish National Space Agency, declared exploration of the far side of the moon a great achievement by China. “We are very happy to be a part of it,” he said.
International cooperation has enabled scientists from around the world to pool their expertise in space exploration. “I think one of the beauties of space science is that we do cooperate internationally,” opined Robert Wimmer-Schweingruber, a participating scientist from Germany. “Space science is important to me personally, but also as a message of peace worldwide.”
In scientists’ eyes, exploring the unknown is human nature and a cause that transcends national borders. “The moon is a mysterious world to us,” said Wu Weiren, who led China’s first soft landing on the moon in 2013 with the Chang’e-3 mission. “We have a responsibility to explore and understand it. Knowing it will help deepen our understanding of Earth and thereby human beings.”
Internationally, humans had previously made three close contacts with the far side of the moon. About 60 years ago, the former Soviet Union received the first images of it sent back by its Luna-3 probe. And some 10 years later, three U.S. astronauts on the United States Apollo-8 mission saw the bumpy dark sides dotted with impact craters with their own eyes. Now, China presses forward to make greater study of it possible.
“Although we still don’t yet know what we might find, exploration could influence several generations,” noted Shen Zhenrong, a designer of the lunar rover.
Scientists consider the far side of the moon much older than the front side and believe that studying the shallow lunar surface structure there might be inspirational for learning about the origin and evolutions of the moon, stars and galaxies.
Successful landing on the far side is also conducive to astronomical observation, according to Shen. “Surrounding ionized stratum makes it hard to receive lowfrequency space spectrum on Earth,” explained Shen. “The body of the moon shields against radio interference from Earth, making the dark side an ideal place for low-frequency radio astronomical observation.”
How much water is on the moon? How does radiation there affect astronauts? Can mankind send more people there? These questions have been puzzling scientists worldwide. The lunar exploration program doesn’t end with a specific goal. As the Chang’e-4 mission finishes tasks like detecting the mineral composition and measuring the neutron radiation and neutral atoms, people will learn more about the moon and get closer to answers to such questions.