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On Friday, China launched a second lander to the lunar far side. If the mission is successful, it will be the first in history to bring back a sample from the part of the moon that Earth never sees.

The mission is called Chang’e-6, named after the Chinese moon goddess and pronounced “chong-uh.” It lifted off on time at 5:27 p.m. local time under gloomy skies from the Wenchang space site on Hainan Island in southern China, carried to space by a Long March 5 rocket. About 32 minutes after the launch, the spacecraft separated from the rocket and the mission proceeded on a 5-day journey to the moon.

Why the far side of the moon?

Unlike Earth, whose erosion and shifting crust constantly renew its surface, the moon remains frozen in time. By studying samples from different parts of the lunar surface, scientists seek information about the origin and evolution of Earth’s satellite. But so far, the United States, the former Soviet Union and China have gathered samples only from the near side of the moon.

The far side of the moon — it is not actually the dark side of the moon — is distinct from the near side. It has a thicker crust, more craters and fewer maria, or plains where lava once flowed. But no one really knows why the two sides of the moon are so different.

“People want to know why this happened,” said Yi Xu, a professor at the Space Science Institute of Macau University of Science and Technology and a member of the Chang’e-6 science team. “If we can collect some samples on the far side, then we can maybe get some clues to these questions.”