Chang'e-5: Lunar Sampling and Dating the Returned Material

Chang'e-5 undertook the uncrewed sample-return task in the Chinese lunar exploration programme's sequence of orbiting, landing and returning, linking observations on the lunar surface with analysis in terrestrial laboratories. The China National Space Administration organized the mission; the China Academy of Space Technology led development of the spacecraft; the China Academy of Launch Vehicle Technology was responsible for the rocket; and the National Astronomical Observatories of the Chinese Academy of Sciences handled the ground application system and the receipt and management of scientific data and samples.

The spacecraft comprised an orbiter, return capsule, lander and ascender. Near the Moon, it separated into two combinations: one remained in orbit while the other descended to collect samples, which were subsequently transferred through a rendezvous in lunar orbit. The planned launch schedule had been delayed by launcher problems, and the mission ultimately flew in 2020.

Northeastern Oceanus Procellarum was selected to obtain young mare basalts not covered by earlier sampling missions. The landing site was approximately 43.058° north and 51.916° west, at a higher latitude than the Apollo and Luna sampling sites. Relatively flat mare terrain predominates there, but impact craters, wrinkle ridges and rilles also occur in the region. Remote-sensing geological surveys supplied the spatial context for interpreting the samples.

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At 04:30 Beijing time on 24 November 2020, the Long March 5 Y5 launch vehicle sent Chang'e-5 toward the Moon from Wenchang, Hainan. At 20:58 on 28 November, the spacecraft began a braking maneuver near the Moon and entered lunar orbit after its engine fired for about 17 minutes. This phase achieved gravitational capture; further orbital adjustments were then needed to prepare for descent.

On 1 December, the lander–ascender combination landed in the preselected region on the Moon's near side. The other combination remained in orbit rather than descending with it, waiting for the ascender after completion of surface operations. This division of responsibilities linked lunar sampling, orbital reception and the return to Earth as successive flight phases.

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Lunar sampling used both drilling and surface collection. The drill obtained a regolith core about one meter long, with a flexible sampling bag collecting and preserving subsurface material. Guided by camera images, the robotic arm collected surface regolith and rock fragments near the lander. The two types of samples were initially packaged separately and then placed in the sealed container on the ascender.

The landing and panoramic cameras recorded landforms; the Lunar Mineralogical Spectrometer observed spectra in the sampling area; and the Lunar Regolith Penetrating Radar assisted in assessing subsurface structure. The instruments' location-specific information allowed terrestrial laboratories to relate the samples to the environments from which they had been collected.

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On 3 December, the ascender lifted off from the lunar surface and entered orbit. On 6 December, it rendezvoused and docked with the orbiter–return-capsule combination and transferred the samples to the capsule. The ascender then separated, while the orbiter and return capsule waited before beginning the Moon-to-Earth transfer.

On 17 December, the return capsule separated from the orbiter, slowed through two atmospheric entries, and finally descended by parachute. At 01:59 Beijing time, it landed in the designated area of Siziwang Banner, Inner Mongolia. The mission returned 1,731 grams of lunar samples. After recovery, the sealed container was taken to Beijing, shifting the work from surface operations to sample preservation, cataloguing and laboratory research.

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The preliminary study published by Chunlai Li, Hao Hu, Meng-Fei Yang and colleagues did not treat the returned regolith as a single homogeneous rock. Researchers selected 155 milligrams of surface-collected material for particle statistics, using microscopic images to measure particle size and shape and carrying out microscopy, mineral identification and chemical analyses on rock fragments.

The particle statistics differed according to the basis of measurement. By number, 95 percent of particles had equivalent diameters between 1.40 and 9.35 micrometers; by mass, 95 percent fell between 4.84 and 432.27 micrometers. The contribution of a few larger particles to total mass therefore cannot be inferred directly from their proportion by count.

The material observed included basalt fragments, agglutinates, glass and a small amount of breccia. The basalt fragments consisted mainly of pyroxene, feldspar, olivine and ilmenite; the overall chemical composition showed relatively high ferrous oxide and a low magnesium number. The researchers related the samples to mare basalt and discussed the role of fragmentation and weathering of local bedrock in forming the regolith.

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In 2021, Qiu-Li Li, Qin Zhou, Yu Liu and other researchers analyzed basalt fragments in the returned samples. The team selected representative particles with different rock textures and measured lead isotope compositions in their minerals, obtaining a crystallization age of 2.030 billion years with an uncertainty of about 4 million years.

This was about 800–900 million years younger than the young mare basalts previously dated directly, confirming that the lunar interior could still generate basaltic magma at a relatively late stage. It also provided an important calibration point for crater-counting chronology: remote-sensing studies can compare surface ages using crater sizes and numbers, but require directly dated physical samples as constraints. Sample return linked the relative age of a particular terrain to an isotopic age testable in the laboratory.

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