That mission, and the 2020 Chang’e-5 robotic mission before it, are the first to return lunar rocks to Earth since the 1970s. Together they are building on what scientists learned from Apollo-era missions, helping to unravel mysteries about how the Moon was formed and why it looks the way it does today, and providing clues about our solar system’s history.
But big puzzles remain, such as why the far side of the Moon—the half that always faces away from Earth—is so radically different from the near side. And what is behind the surprising finding that lunar volcanoes may have been active much more recently than previously thought? “The more we look at the Moon, the more we’ve discovered—and the more we realize how little we know,” says Clive R. Neal, a geologist at the University of Notre Dame who specializes in lunar exploration.
China’s 2024 Chang’e-6 robotic lander mission brought more than four pounds of rocks from the far side of the Moon back to Earth.
Credit:
CNSA / CAS
With NASA planning to send astronauts back to the Moon’s surface in 2027 for the first time since 1972, geologists are excited about what rocks they might find there and the scientific secrets those samples could reveal—along with what resources could be mined for a future Moon base, or for renewable energy back home on Earth.
Origin story
The samples brought home from the Moon in the 1970s by the Apollo missions and the Soviet Union’s Luna missions cleared up quite a lot about the Moon’s history. Because the lunar samples shared strong similarities with Earth rocks, this added weight to the idea that the Moon was formed when a Mars-sized object called Theia collided with the proto-Earth roughly 4.5 billion years ago.
Debris from the impact was thrown into orbit around Earth and eventually coalesced into the Moon. In its early days, the Moon was entirely molten. As the magma ocean cooled over hundreds of millions of years, the Moon formed a crust and a mantle below. Giant pools of lava filled impact craters and settled into the lunar lowlands, or maria (Latin for “seas”), while highlands and volcanic domes loomed above them. Eventually, the volcanism died out.
Without plate tectonics or weather, the only things left to alter the Moon’s cold, dead surface were meteorites. A lot of the Apollo-era samples were found to have formed from the heat and pressure of impacts around 3.9 billion years ago, suggesting that they were the result of a short period of intense pummeling by space rocks called the Late Heavy Bombardment.
But research since the 1970s has refined or changed this picture. Higher-resolution orbital images have revealed plenty of large impact craters that seem far older than 3.9 billion years, for example. And meteorites found on Earth, thought to have been ejected from various areas of the Moon during big impacts, have been found to span a huge range of ages.
All this work together suggests that the asteroid bombardment didn’t happen in one dramatic spike but rather over an extended period lasting from perhaps 4.2 billion to 3.4 billion years ago. In this scenario, the Apollo samples dated to 3.9 billion years likely all came from just one huge impact that spewed rock over a very wide area that happened to include the Apollo-era landing sites.
The Moon: Dead or alive
Greater mysteries surround volcanism on the Moon. “The canonical thing I learned in school was that the Moon had been geologically dead for billions of years,” says Samuel Lawrence, a planetary scientist at NASA’s Johnson Space Center in Houston.
The long-held theory was that a small body like the Moon should have lost its heat to space relatively quickly—and a frigid, extinguished Moon shouldn’t have widespread volcanic activity. Apollo-era samples suggested that most of this volcanism stopped 3 billion years ago or earlier, supporting the theory. But research over the past two decades has overturned that view.
This geologic map of the Moon released in 2022 by China is the most detailed global map yet published and includes information gleaned from the 2020 Chang’e-5 mission.
Credit:
J. JI ET AL / THE 1:2,500,000-SCALE GEOLOGIC MAP OF THE GLOBAL MOON 2022.
In 2014, Lawrence and colleagues posited that some patches of irregular terrain in the middle of the dark plains, or mare, spotted by the NASA Lunar Reconnaissance Orbiter were the result of volcanism that kept going until less than 100 million years ago. “That is totally, totally surprising,” says cosmochemist Qing-Zhu Yin of the University of California, Davis.
The latest sample-return missions added more concrete evidence for recent volcanism. In 2020, the Chang’e-5 robotic mission landed in Oceanus Procellarum (the Ocean of Storms) — a spot picked in part because it looked geologically young given how few craters had accumulated there. Sure enough, the volcanic rocks brought home by that mission were found to be 2 billion years old, the youngest ever retrieved from the Moon. “That was big news,” says planetary geoscientist Jim Head of Brown University, who worked on NASA’s Apollo missions.
On top of this, when researchers trawled through thousands of glass beads found in the Chang’e-5 soil samples, most of which are thought to have been created by impacts, they identified three that were volcanic—and only 120 million years old. This finding was published just last year and still needs to be verified, but if such recent dates hold up, they suggest that the Moon might still be capable of producing deep magma even today, Yin says.
All this indicates that the Moon might not have cooled as fast as everyone thought it did. It’s also possible that some of the younger volcanism could have been powered by radioactive elements underground, which can generate enough heat to form magma and are known to be prevalent in certain patches of the Moon. This could explain the 120-million-year-old volcanic glass beads, for example. But not all the early volcanism can be explained this way: The Chang’e-5 volcanic rocks, along with some 2.8-billion-year-old volcanic rock brought back from the far side by Chang’e-6, came from source rocks not enriched with these elements.
“It throws up more questions than it answers,” Neal says. “It’s job security for people like me — we now have new questions to address.”
