Ancient rocks collected from the far side of the moon are giving scientists a fresh look at the violent history of our solar system.
The rare samples suggest that asteroid impacts on the moon happened over a much longer period than researchers once believed, challenging a theory that has been widely accepted for decades.
The findings, published in Science Advances, are based on rocks returned by China’s Chang’e-6 mission, the first spacecraft to bring samples back from the moon’s far side.
These unique samples are helping scientists better understand not only the moon’s past but also the early history of Earth.
Unlike Earth, the moon has remained largely unchanged for billions of years. Our planet constantly reshapes itself through erosion, volcanoes, earthquakes, and the movement of tectonic plates. These natural processes have erased much of the evidence from Earth’s earliest history.
The moon, however, has no weather, no oceans, and no active plate tectonics. As a result, its surface has preserved a record of asteroid impacts dating back to the formation of the solar system. Scientists often describe the moon as a natural time capsule because it has kept this ancient history almost intact.
Until recently, nearly all lunar samples came from the side of the moon that always faces Earth. The Chang’e-6 mission changed that by collecting rocks from the far side, giving researchers the first opportunity to compare both halves of the moon.
Scientists analyzed tiny pieces of these rocks using a technique that measures radioactive elements to determine when the rocks were heated by asteroid impacts. The study identified impact events that occurred between about 4.33 billion and 1.13 billion years ago, allowing researchers to reconstruct more than three billion years of the moon’s history.
For many years, many scientists believed the moon experienced a short but extremely intense period of asteroid impacts known as the Late Heavy Bombardment. According to this idea, countless asteroids struck the moon and other planets in a relatively brief period around four billion years ago.
The new evidence paints a different picture. Instead of one sudden wave of impacts, the study suggests that asteroid collisions gradually became less common over hundreds of millions of years. This slower decline changes scientists’ understanding of how the early solar system developed after the planets formed.
The discovery is important because the moon and Earth formed at about the same time and have shared much of their history. Every major asteroid impact recorded on the moon likely reflects similar events that affected the young Earth. Since Earth’s ancient impact record has mostly disappeared, the moon provides valuable clues about conditions on our own planet billions of years ago.
Learning when these impacts happened can help scientists understand how Earth’s environment evolved during its earliest years. Large asteroid collisions may have influenced the planet’s surface, atmosphere, oceans, and even the conditions that eventually allowed life to emerge.
The study also highlights the scientific value of exploring the moon’s far side. Because this region experienced fewer later geological changes than the near side, it preserves a clearer record of the earliest events in the solar system.
As new lunar missions continue to return samples and gather data, scientists expect to uncover even more secrets hidden in the moon’s ancient rocks. Each new discovery helps piece together the story of how the moon, Earth, and the rest of the solar system evolved over billions of years.
