China achieved a historic feat by bringing back the first-ever 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. These samples were returned to Earth on June 25, 2024.
Chang’e 6 built on the achievements of two previous Chinese 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 brought back samples from the near side of the moon.
Scientists expect the Chang’e 6 samples will not only provide important geological knowledge about the moon, but also improve their understanding of Earth and the early history of the solar system.
Lunar scientists like me have been fascinated by the far side of the Moon since the Soviet Union’s Luna 3 mission in 1959, which showed that the far side of the Moon looks very different from the near side.
The back of the moon
Because the same side of the moon always faces Earth, the far side can only be seen from spacecraft. The far side is not permanently dark – it cycles between two weeks of daylight and two weeks of night, just like every other location on the moon.
Images taken by spacecraft show that about a third of the surface on the near side of the Moon is made up of dark, smooth plains, while only about 1% of the far side of the Moon is made up of such plains.
These dark plains were once volcanic lava flows, similar to those on Earth in Hawaii, eastern Washington, and India.
Images taken from orbit around the moon 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 made soft landings on the near side. A landed mission on the far side is more difficult because mission control cannot directly see or talk to the spacecraft. So what is needed is a second spacecraft to relay information between the lander and Earth. China used its Queqiao-2 satellite, which is set to launch in March 2024.
Chang’e 6’s touchdown
On June 6, 2024, Chang’e 6 landed in the colossal South Pole-Aitken Basin, which is about 2,500 kilometers (1,600 miles) wide and 8 kilometers (5 miles) deep. It is the solar system’s largest impact structure: a bowl-shaped feature created when an asteroid collided with a celestial body, causing a massive explosion.
On top of the South Pole-Aitkin is a slightly younger and much smaller impact zone, the Apollo Basin, with a diameter of about 492 kilometers.
Impact basins expose the moon’s deep interior, much like a drill core. For example, the impact that created the South Pole-Aitkin Basin may have removed some of the lunar crust, exposing material deep inside the moon—as deep as 62 miles (100 km). The subsequent Apollo impact would have removed even more material. So 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. By analyzing the composition of the volcanic rocks that Chang’e 6 brought back, scientists may be able to figure out why the near side has so many more volcanic deposits. Scientists can also compare the ages of these far-side rocks to rocks from near-side volcanic eruptions that occurred about 3.9 to 3.2 billion years ago.
By measuring the true age of the rocks, scientists can refine other methods, such as counting craters, which are used to estimate the age of surface formations on planets.
Because planetary surfaces accumulate more craters as they age, researchers can estimate the age of a planet’s surface by comparing the number of craters they can count to the number of craters generated by a simulated model. But counting craters isn’t very accurate: real rock samples can help researchers improve these methods.
Uncovering Secrets from the Moon’s Molten Past
Researchers believe that the Moon, along with some rocky planets, was once almost completely molten. So for a brief period early in its history, the Moon was simply lava with little or no solid rock.
Chang’e 6’s landing site could contain materials from the moon’s mantle — the layer beneath the crust. These samples could help scientists understand how the moon evolved from a magma ocean to a geologic layer — a solidified crust, mantle and core.
Data from these samples can also provide clues about the evolution of Earth in the final stages of planet formation. Scientists predict that about 4 billion years ago, many asteroids and comets crashed into rocky planets like Earth. We call this period the “lunar catastrophe.” By studying certain rocks from crater impacts on the moon, scientists can learn more about this era.
Because the South Pole-Aitkin Basin is the oldest well-preserved structure on the Moon, it could provide evidence about whether the number of basin-forming impacts occurred over a longer period, such as 500 million years, or a shorter period, such as 200 million years. Knowing the time scale would help gauge the intensity of the impacts during the formation of the Solar System.
A scientific gift from the other side
Extraterrestrial material – such as samples from the Moon, Mars, asteroids and comets – are gifts that keep on giving.
Scientists will curate and maintain these samples in laboratories to keep them pristine. This process will distribute some of the precious samples for analysis with state-of-the-art equipment. The rest will be stored for future generations of scientists to investigate new questions that will arise decades from now.
Science makes the most progress when scientists share ideas, data, and samples. In late 2023, the China National Space Administration made the Chang’e 5 samples available to a group of international researchers. I expect a similar sample-sharing program for the Chang’e 6 samples.
However, this sharing doesn’t go both ways. NASA can’t share the samples it curates directly with Chinese researchers because of the Wolf Amendment, which prohibits NASA from using funds to collaborate with China on any programs.
China’s future plans for lunar exploration 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 ice form. NASA’s recently canceled VIPER rover had similar goals. These missions will help China figure out where to put its International Lunar Research Station, scheduled for 2030.
This article is republished from The Conversation, a nonprofit, independent news organization that brings you facts and reliable analysis to help you understand our complex world. It was written by: Jeffrey Gillis-Davis, Arts and Sciences at Washington University in St. Louis
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Jeffrey Gillis-Davis is not an employee of, an advisor to, an owner of stock in, or a recipient of funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond his academic appointment.