The materials brought back from the Moon—comprising rocks, soil, and core samples—represent some of the most valuable extraterrestrial matter available for scientific study. These samples hold the record of the Moon’s geological history and the early solar system. Unlike materials analyzed remotely by robotic probes, these returned specimens can be subjected to increasingly sophisticated laboratory techniques over decades. This ability to re-examine them with new, precise instrumentation makes them a continuously yielding resource for planetary science.
How Lunar Samples Were Collected
The vast majority of lunar samples were collected during the six crewed NASA Apollo missions between 1969 and 1972, which were meticulously planned geological expeditions. Astronauts employed specialized tools, including tongs, scoops, and core tubes, to collect documented samples from the lunar surface and subsurface. The six Apollo missions returned approximately 382 kilograms (842 pounds) of material from diverse geological regions.
The Soviet Union also successfully collected and returned lunar material through its automated Luna program. Between 1970 and 1976, three robotic probes—Luna 16, 20, and 24—returned about 300 grams of soil from three distinct sites on the Moon’s near side. More recently, China’s robotic Chang’e missions have renewed global sample collection efforts. The Chang’e 5 mission returned 1.731 kilograms of material from a geologically young volcanic region, and the Chang’e 6 mission returned 1.935 kilograms from the far side of the Moon.
Physical Characteristics of Lunar Samples
The returned lunar material falls into two categories: solidified rock and fragmented soil, both shaped by the Moon’s airless environment. The solidified rocks include dark, dense basalts, which formed from ancient lava flows and are rich in iron and titanium, composing the dark plains known as the maria. In contrast are the light-colored anorthosites from the lunar highlands, which are dominated by calcium-rich plagioclase feldspar. This compositional difference reflects the early cooling and differentiation of the Moon’s crust.
The fine, dusty soil, called regolith, is produced by the continuous bombardment of micrometeorites shattering surface rocks. This process results in abrasive, sharp-edged particles, unlike terrestrial soil, which is smoothed by wind and water erosion. A unique component in the regolith is the presence of agglutinates, which are tiny glass-bonded particles created when micrometeorite impacts melt and fuse surrounding material, embedding microscopic specks of pure iron. The Moon’s lack of atmosphere and the constant stream of hydrogen from the solar wind create a chemically reduced environment, explaining the lack of hydrated minerals and oxidized iron in most returned samples.
Protecting and Curating the Samples
The long-term preservation of the lunar collection is handled by specialized curation facilities, with the primary repository located at the Johnson Space Center (JSC) in Houston, Texas. To prevent terrestrial contamination and preserve the pristine state of the material, most samples are stored in specialized vaults either in a vacuum or under a controlled, inert atmosphere of ultra-pure nitrogen. This curation ensures that the samples remain chemically and physically unaltered for study by future generations of scientists.
Researchers worldwide must follow a formal process to gain access to the collection. Investigators, known as Principal Investigators, submit a detailed request to the Apollo Sample Curator, outlining their scientific goals and the specific analytical techniques they intend to use. These proposals undergo a peer-review process by the Lunar Sample Subcommittee of the Curation and Analysis Planning Team for Extraterrestrial Materials (CAPTEM). This review process is designed to maximize the scientific return from the samples while ensuring that this irreplaceable material is preserved.
Major Scientific Discoveries
Analyzing the composition and age of the lunar samples has provided the primary evidence supporting the Giant Impact Hypothesis, the leading theory for the Moon’s formation. The identical ratios of stable oxygen isotopes found in both lunar and terrestrial rocks suggest a common origin, consistent with the theory that a Mars-sized body collided with the proto-Earth, and the debris coalesced to form the Moon. Further support comes from the anorthositic composition of the lunar highlands, which indicates that the Moon was once covered by a global magma ocean, with the lighter, plagioclase-rich minerals floating to the surface to form the crust.
Geochronological analysis, particularly the highly precise uranium-lead (U-Pb) dating of tiny zircon crystals, has provided a timeline for the Moon’s early history. These mineral grains indicate that the Moon’s crustal differentiation began approximately 4.51 billion years ago, placing the formation event within the first 60 million years of the solar system’s existence. Furthermore, impact-melt rocks collected from various landing sites have revealed a distinct clustering of ages between 3.8 and 4.1 billion years ago. This data supports the concept of the Late Heavy Bombardment, a hypothesized period when the inner solar system experienced a dramatic spike in asteroid and comet impacts. The ability to date this event using lunar samples has allowed scientists to establish a chronological framework for the entire inner solar system, including Mars and Mercury.