China brought a capsule full of lunar soil from the far side of the moon down to Earth on Tuesday, achieving the latest success in an ambitious schedule to explore the moon and other parts of the solar system.
The sample, retrieved by the China National Space Administration's Chang'e-6 lander after a 53-day mission, highlights China's growing capabilities in space and notches another win in a series of lunar missions that started in 2007 and have so far been executed almost without flaw.
"Chang'e-6 is the first mission in human history to return samples from the far side of the moon," Long Xiao, a planetary geologist at China University of Geosciences, wrote in an email. "This is a major event for scientists worldwide," he added, and "a cause for celebration for all humanity."
Such sentiments and the prospects of international lunar sample exchanges highlighted the hope that China's robotic missions to the moon and Mars will serve to advance scientific understanding of the solar system. Those possibilities are contrasted by views in Washington and elsewhere that Tuesday's achievement is the latest milestone in a 21st century space race with geopolitical overtones.
In February, a privately operated American spacecraft landed on the moon. NASA is also pursuing the Artemis campaign to return Americans to the lunar surface, although its next mission, a flight by astronauts around the moon, has been delayed because of technical issues.
China, too, is looking to expand its presence on the moon, landing more robots there, and eventually human astronauts, in the years to come.
Building toward that goal, it has taken a slow and steady approach, executing a robotic lunar exploration program it devised decades in advance. Named after the Chinese moon goddess Chang'e (pronounced "chong-uh"), the program's first two missions orbited the moon to photograph and map its surface. Then came Chang'e-3, which landed on the lunar near side in 2013 and deployed a rover, Yutu-1. It was followed in 2019 by Chang'e-4, which became the first vehicle to visit the moon's far side and put the Yutu-2 rover on the surface.
One year later, it landed Chang'e-5, which sent nearly 4 pounds of near-side lunar regolith to the Earth. The achievement made China only the third country -- after the United States and the Soviet Union -- to achieve the complex orbital choreography of collecting a sample from the moon.
According to Yuqi Qian, a lunar geologist at the University of Hong Kong, the maneuvers of Chang'e-5 and Chang'e-6 are both test runs for China's future crewed missions to the moon, which, like the Apollo missions of the 1960s and '70s, need to land and then launch humans from the lunar surface.
While it works toward putting astronauts on the moon, China's long-term strategy is paying scientific benefits for understanding the solar system.
The Chang'e-5 sample was younger than the lunar material collected by the Americans or Soviets in the 1960s and '70s. It is made up mainly of basalts, or cooled lava from ancient volcanic eruptions.
Two Chinese-led research teams concluded that the basalts were about 2 billion years old, suggesting that volcanic activity on the moon extended at least a billion years beyond the time frame deduced from the U.S. Apollo and Soviet Luna samples.
Other studies of the material ruled out theories about how the moon's insides had warmed enough to generate volcanic activity. One research group found that the amounts of radioactive elements in the lunar interior, which could decay and produce heat, were not high enough to cause the eruptions. Another result ruled out water in the mantle as a potential source of the interior melting that led to volcanism.
Chang'e-6 launched May 3 with even grander scientific ambitions: bringing back material from the far side of the moon. The near side of the moon is dominated by wide, dark plains where ancient lava once flowed. But the far side has fewer of those plains. It also has more craters and a thicker crust.
And because that half never faces Earth, it is impossible to directly communicate with landers on the lunar far side, making it difficult to reach successfully. The Chinese space agency relied on two satellites it previously launched into orbit around the moon, Queqiao and Queqiao-2, to remain in touch with Chang'e-6 during its visit.
The spacecraft used the same technique as Chang'e-5 to reach the moon and then return its sample to Earth.
After a few weeks in lunar orbit, Chang'e-6 descended to a site at the edge of the South Pole-Aitken basin, the oldest, deepest impact crater on the moon. Equipped with a mechanical scoop and a drill, the lander spent two days gathering lunar rock and dust from its surroundings and the moon's subsurface.
It then stashed the material away. The mission deployed a miniature rover that snapped a picture of the lander with a small Chinese flag raised. Then, on June 3, a rocket flung the sample canister back into lunar orbit. The materials then reunited on June 6 with a spacecraft that had remained in orbit and prepared to begin the journey back to Earth.
On Tuesday, the sample container reentered Earth's atmosphere and then parachuted to the surface of the Siziwang Banner area of Inner Mongolia, where ground crews worked to recover it.
When scientists take possession of the far-side soils, they will compare the composition of the newly recovered basalts with those from the lunar near side. That may help them deduce how the moon's volcanic activity caused its two halves to evolve differently.
The mission team will also be looking for material from surrounding regions, blasted away from their original sites by impacts with comets and asteroids. If strong enough, these collisions may have excavated material from the lower crust of the moon and its upper mantle, Qian said. That could lead to insights about the structure and composition of the lunar interior.
Melted rock from those impacts could also yield clues about the age of the South Pole-Aitken basin and the era in which it formed, during which scientists believe a barrage of asteroids and comets bombarded the inner solar system.
This period "totally changed the geological history of the moon," Qian said, and was also "a critical time for the evolution of the Earth."
Clive Neal, a planetary geologist at the University of Notre Dame, called the goals lofty, but he is looking forward to the discoveries that will follow the sample's return. Referring to China's streak of lunar success thus far, "it's excellent," he said. "More power to them."
Strained political relations, however, will make it challenging for American scientists to collaborate with Chinese researchers on studying the far-side samples.
The Wolf Amendment, enacted in 2011, prohibits NASA from using federal funds for bilateral cooperation with the Chinese government. Federal officials recently granted the space agency an exemption, which allowed NASA-funded researchers to apply for access to the near-side sample retrieved by Chang'e-5. But another bill passed by the U.S. House of Representatives in June would ban universities with research ties to Chinese institutions from receiving funding from the U.S. Department of Defense.
For the future, China has its eyes set on the lunar south pole, where Chang'e-7 and 8 will explore the environment and search for water and other resources. It hopes to send crewed missions to the moon by 2030. Eventually, China plans to build an international base at the south pole.
NASA's Artemis campaign is also shooting for the lunar south pole. Bill Nelson, the space agency's administrator, has previously referred to the parallel programs as a race between the United States and China.
Many scientists reject that framing. Resources for studying the moon plunged after American astronauts beat the Soviets to the lunar surface in 1969, Neal said. "I don't like international space races, because they're not sustainable," he said. "A race is to be won. Once you win it, then what?"
He added, "I think it's important to look at space as something that can bring us together, rather than tear us apart."
Several countries contributed payloads that flew with the Chang'e-6 mission, including France and Pakistan. Chinese researchers took this as a good sign for the future.
"Lunar exploration is a shared endeavor for all humanity," Xiao said, adding that he hopes for increased international collaboration, "particularly between major spacefaring nations like China and the United States."