China is launching a second lander to the lunar far side, which, if successful, will be the first mission in history to bring back a sample from the part of the moon that Earth never sees.
Unlike Earth, whose erosion and shifting crust constantly renew its surface, the moon remains frozen in time. Scientists hope that retrieving material from the far side will reveal information about the origin and evolution of the Earth-moon system.
The mission is called Chang'e-6, named after the Chinese moon goddess and pronounced "changa."
Chang'e-6 is scheduled to launch Friday at 5:27 am Eastern time from the Wenchang space site on Hainan Island in southern China. A live broadcast of the launch is expected to be available on the China Global Television Network, a Chinese state news service, beginning at 4:30 am Eastern time.
Chang'e-6 will be carried to space by a Long March 5 rocket. If the weather does not cooperate Friday, a backup launch window of the same duration has been reserved for the following day.
Chang'e-6 is the latest in a series of Chinese lunar missions designed to orbit or land on the moon. It will be the first probe to bring back samples from the lunar far side.
The first to visit that half of the moon, in 2019, was Chang'e-4, which included a rover to explore the moon's Von Karman crater. One year later, Chang'e-5 gathered nearly 4 pounds of regolith from the moon's near side and brought it to Earth. Scientists in other countries, including some in the United States, recently petitioned to study those samples.
It will take Chang'e-6 about a month after launch to reach the moon's far side, and another month to come back.
An orbiter will circle the moon while the mission's lander descends to the lunar surface. The lander will gather soil from the surface using a mechanical arm and collect a subsurface sample from as far down as 6.5 feet with a drill. A vehicle on the lander will then lift off from the moon, passing the sample on to the orbiter's reentry module for its return back to Earth.
The United States, the former Soviet Union and China have successfully gathered samples from the near side of the moon and brought them to Earth. But 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. With a lunar far side sample, scientists can begin to probe why the two sides of the moon are so different.
The mission will collect material from the 1,616-mile-wide South Pole-Aitken basin. The impact that created the basin -- among the largest in the history of the solar system -- is thought to have dug up material from the lunar mantle. If that material can be retrieved, scientists can learn more about the history of the moon's insides.
Because the same side of the moon always faces Earth, it is impossible to directly establish communications with the lunar far side. In 2018, China sent the Queqiao satellite into lunar orbit to relay information from Chang'e-4 to Earth. In March, it launched a second satellite called Queqiao-2. The pair will be used in tandem to remain in contact with Chang'e-6 during sample collection.
China's lunar exploration program is one facet of the nation's growing presence in space, which includes missions to Mars and future visits to asteroids. The Chang'e mission series was designed in the 1990s and, so far, has a 100 per cent success rate. Its next two probes are already in development.
Chang'e-7, expected to launch in 2026, will search for water at the lunar south pole. Chang'e-8 will survey material in the same region that could potentially be used to build future infrastructure, according to the China National Space Administration.
China hopes to send crewed missions to the moon by 2030 and is also working on establishing a permanent, international lunar research base in the 2030s.