China achieved a historic feat by returning the first sample from the far side of the moon in June 2024. The lunar lander Chang’e 6 used a robotic scoop and drill to collect about 5 pounds (2 kilograms) of rocks and soil. Those samples were returned to Earth on June 25, 2024.
Chang’e 6 built on the successes of China’s two previous missions: Chang’e 4, which made a soft landing on the far side of the Moon and used a rover to explore the surface, and Chang’e 5, which returned samples from the near side of the Moon.
Scientists expect the Chang’e 6 samples to not only provide important geological information about the Moon, but also improve their understanding of the early history of Earth and the solar system.
Lunar scientists like me have been interested in the dark side of the Moon since the Soviet Union’s Luna 3 mission in 1959. That mission revealed that the dark side of the Moon looks very different from the dark side.
Dark side of the Moon
Because the same side of the Moon always faces Earth, you can only see the far side with spacecraft. The far side is not permanently dark – it alternates between two weeks of day and two weeks of night, just like anywhere else on the Moon.
Images taken by spacecraft show that about a third of the Moon’s near side consists of dark, flat areas, while only 1 percent of the far side consists of these areas.
These dark plains were once volcanic lava flows similar to those found on Earth in Hawaii, eastern Washington, and India.
Images taken from lunar orbit show researchers that these plains once contained volcanic vents, cones, domes, collapsed pits and channels.
Only the Chang’e 4 and Chang’e 6 missions have landed on the far side of the moon, while 25 spacecraft have successfully soft-landed on the near side. A mission to the far side is more difficult because mission control cannot see or talk to the spacecraft directly. So what is needed is a second spacecraft to transmit information between the lander and Earth. China used its orbiting satellite Queqiao-2, which was launched in March 2024.
Chang’e 6’s goal
On June 6, 2024, Chang’e 6 landed in the massive South Pole-Aitken basin, which is about 1,550 miles (2,500 km) wide and 5 miles (8 km) deep. It is the solar system’s largest impact structure: a bowl-shaped structure formed when an asteroid hits a body, causing a tremendous explosion.
Above South Pole-Aitkin lies the Apollo basin, a slightly younger and much smaller impact structure with a diameter of about 308 miles (492 km).
Impact basins expose the deep interior of the Moon, like a drill core. For example, the impact that created the South Pole-Aitkin basin may have removed some of the Moon’s crust and exposed material deep inside the Moon—as much as 62 miles (100 km) down. The later Apollo impact would have removed even more material. Therefore, the returned samples will likely contain some rocks that are different from those in the current sample collection.
Chang’e 6 landed here on some of the sparse, far-side volcanic deposits. Analyzing the composition of the volcanic rocks that Chang’e 6 brings back could help researchers understand why there is so much volcanic deposit on the near side. Scientists will also be able to compare the ages of these far-side rocks to rocks from near-side volcanic eruptions that occurred about 3.9 billion to 3.2 billion years ago.
Measuring the true age of rocks will help scientists improve other methods, such as crater counting, which is used to estimate the age of planetary surface formations.
Because planetary surfaces accumulate more craters the longer they’ve been around, researchers can estimate the age of a planet’s surface by comparing the number of craters they can count to those created by a simulated model. But crater counting isn’t very accurate — having real rock samples could help researchers figure out how to improve these methods.
Revealing secrets from the Moon’s molten past
Researchers assume that the Moon, along with some rocky planets, was almost entirely molten — meaning that for a brief period early in its history, the Moon was lava with little or no solid rock.
Chang’e 6’s landing site could contain material from the Moon’s mantle – the layer beneath its crust. These samples could help scientists understand how the Moon evolved from a magma ocean into geological layers – the solidified crust, mantle and core.
Data from these samples could also provide clues about Earth’s evolution during the final stages of planet formation. Scientists estimate that rocky planets like Earth were rained down with a huge number of asteroids and comets around 4 billion years ago. We call this period the “lunar cataclysm.” Studying specific rocks from impact craters on the Moon could help scientists learn more about this period.
Because the South Pole-Aitkin basin is the oldest well-preserved structure on the Moon, it may contain evidence of whether the number of basin-forming impacts occurred over a longer time period, such as 500 million years, or a shorter time period, such as 200 million years. Knowing the time scale will help gauge the intensity of impacts during the formation of the solar system.
A scientific gift from far away
Extraterrestrial materials, such as samples from the Moon, Mars, asteroids, and comets, are gifts that continually give us gifts.
Scientists will keep these samples intact by organizing and preserving them in laboratories. This process will distribute some of the valuable samples to be analyzed with state-of-the-art equipment. The rest will be preserved for future generations of scientists to explore new questions decades from now.
Science progresses most when scientists share ideas, data, and samples. By the end of 2023, the China National Space Administration made samples from Chang’e 5 available to a number of international researchers. I expect to see a similar sample-sharing program for Chang’e 6 samples.
But this sharing doesn’t go both ways. NASA cannot share curated samples directly with Chinese researchers because of the Wolf Amendment, which prevents NASA from using funds to collaborate on any programs with China.
China’s future lunar exploration plans include the Chang’e 7 and 8 missions, scheduled for 2026 and 2028 respectively. These missions will land at the South Pole to search for water ice, carbon dioxide ice (also known as dry ice), and methane in the form of ice. NASA’s recently canceled VIPER rover had similar goals. These missions will help China figure out where to put the International Lunar Research Station, planned for 2030.
This article is republished from The Conversation, a nonprofit, independent news organization that brings you facts and trusted analysis to help you understand our complex world. By Jeffrey Gillis-Davis Arts and Sciences at Washington University in St. Louis
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Jeffrey Gillis-Davis does not work for, consult, own shares in, or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond his academic appointment.