Unraveling Chang'e-6: Chinese scientists set to explore first samples from moon's far side

At the Chinese Lunar Sample Laboratory, Chinese scientists are preparing to study the world's first lunar samples from the moon's far side.

The samples, which were collected as part of the Chang'e-6 mission, were transferred to a re-entry vehicle on Thursday, according to the China National Space Administration (CNSA).

The ascender of the Chang'e-6 lunar probe, carrying the moon samples, performed an unmanned rendezvous and docking with the orbiter-returner combination in lunar orbit, the CNSA said, adding that this is the second time China has achieved the maneuver, following the groundbreaking success of the Chang'e-5 mission in 2020.

Located in Beijing, the lunar laboratory of the National Astronomical Observatories (NAOC) is equipped with a room designated for unsealing samples, a middle room for samples collected by the Chang'e-5 probe, and an innermost room reserved for samples collected by the Chang'e-6 probe.

Zhou Qin, deputy chief designer of the ground application system of Chang'e-6 mission, told China Media Group (CMG) that "once the samples are here, we will conduct preliminary studies on their physical properties and chemical components." 

"We have made all the necessary preparations, including the availability and functionality of instruments commonly used for chemical component analysis, such as microscopes, scanning electron microscopes, and electron probes," she added.

The lab serves as a receiving and distribution center for both the Chang'e-5 and future Chang'e-6 samples. Samples collected by Chang'e-5 have been embedded in resin for scientific studies.

"Small rock fragments or lunar soil were embedded in resin to create these slices of samples. Scientists can directly use these slices for various analyses, including isotope and chemical component analyses. We can see that these slices contain two particles, and we have also created a slice using lunar soil, which is extremely fine," Zhou said.

The CNSA has completed the distribution of six batches of Chang'e-5 lunar samples to domestic institutions. Foreign scientists and institutions are permitted to apply for the samples in the seventh batch.

Embedding the samples in resin not only preserves the original shape of the sample particles, but also ensures long-term preservation and use. "These are the seventh batch of slices of samples to be distributed. The seventh batch consists of five sample slices, and we have prepared them all for distribution," Zhou said.

No contamination storage

The NAOC allows for the long-term storage of the samples in a high purity nitrogen environment and ensures there is no contamination during the research process. For example, there is a cabinet filled with nitrogen used for sample unsealing at the lab, where lunar samples collected by the previous Chang'e-5 probe were unsealed.

"The cabinet is filled with nitrogen with pressure inside which is designed to be a little bit higher than the pressure outside, so as to prevent air from getting inside to pollute the samples," said Zhou.  

Lunar samples to be brought back by the Chang'e-6 mission will also be unsealed in the cabinet and distributed to scientists for research. According to the lab, lunar samples brought back by the Chang'e-5 mission were categorized and stored based on the standard of "whether they had been exposed to the air."

"The samples, once exposed to the air, can be further divided into two categories. One is the rock samples that we picked out from the lunar soil which are numbered and stored separately. We have already weighed them and taken pictures of the rocks by exposing them to the air. The other is the returned samples that we have already released to the public," Zhou said.

"According to the requirements of China's Lunar Exploration and Space Engineering Center, the samples lent out, as long as there is a surplus, must be returned to us. The returned samples can be re-applied and reused by scientists for further research," she added.

The lunar samples which have not been exposed to the air are kept in a nitrogen-filled, sealed cabinet.

"The 10 bottles here are used to store original samples collected with a sampling shovel. They are very fine with an average particle size of about 50 microns, which is similar to the thickness of a flour particle. We divided about 150 grams of samples into each bottle. As we distributed the samples to institutions for research, some bottles are one third or half filled. There are also some borehole samples stored here on the shelve, which have never been exposed to the air," said Zhou.

"At present, the lunar samples we keep at the lab are available for distribution. According to the initial plan, 10 percent of the samples have been kept for remote and permanent backup storage, which means we have made preparations for reserving and sub-sampling," she said.