Water on Moon? Chinese laboratory makes discovery in rock samples

Researchers have analyzed the lunar rock samples sent back by the Chinese Lunar Lander Chang’E-5 and found them to have traces of water. The findings were published in the journal Nature

Chang’E was sent to the Moon in December of 2020, where it collected samples of rocks and soil from the lunar surface. The onboard spectral analysis confirmed the presence of water in real-time in the samples. Two days later, a rocket was fired off from the Moon with these samples and landed on Earth two weeks later. Researchers have been studying these samples in further detail and have now found evidence of water in them.

But is it lunar water?

On analysis of the rocks and soil, the researchers found that the samples, on average, contained 30 hydroxyl parts per million. Hydroxyl is the name given to a molecule that contains one atom of hydrogen — and one atom of oxygen is often the result of water reacting with some matter. 

Researcher Parvathy Prem, who was not involved in the research, told New Scientist that the amount of water found during this mission was lower than expected. The fact that the samples were taken at a time when lunar temperatures were close to 200oF (93oC) may have also contributed to this.

Scientists wanted to confirm that the water present on the surface indeed belongs to the Moon. Solar winds also contain hydrogen molecules that can combine with oxygen on the surface to form water molecules. Such molecular are usually found in glassy structures and were also found during previous missions to the Moon, such as Apollo 11. These were tested in the early 2000s, a press release provided by the Chinese Academy of Sciences said. 

The researchers had taken this into consideration and collected samples at a time when solar winds were low. The impact of this decision was evident when Chang’E collected samples containing only a third of such glassy structures compared to the Apollo 11 mission. The bulk of the hydroxyl molecules was found in a phosphate-rich mineral called apatite, which occurs naturally on the Moon as well as on Earth. Interestingly, the apatite crystals contained up to 179 parts per million of water content, New Scientist said in its report.

“This excess hydroxyl is indigenous, demonstrating the presence of lunar-originated internal water in the Chang’E-5 lunar samples, and that water played an important role in the formation and crystallization of the late lunar basaltic magma,” Li Chunlai, corresponding author of the study said in the press release. 

What does it mean for future lunar missions? 

While the presence of water is great news, it is not like we have found an underground spring that will support a human settlement in the near future. However, it does provide information that can be used to estimate water signals in future remote sensing survey data. 

China’s subsequent lunar missions called Chang’E 6 and Chang’E 7 will use a combination of remote sensing and onsite and laboratory testing to better understand the source and distribution of lunar water. 

“By investigating lunar water and its source, we are learning more about the formation and evolution of not just the Moon itself, but also the solar system,” Li added. 

Abstract

The distribution range, time-varying characteristics, and sources of lunar water are still controversial. Here we show the Chang’E-5 in-situ spectral observations of lunar water under Earth’s magnetosphere shielding and relatively high temperatures. Our results show the hydroxyl contents of lunar soils in Chang’E-5 landing site are with a mean value of 28.5 ppm, which is on the weak end of lunar hydration features. This is consistent with the predictions from remote sensing and ground-based telescopic data. Laboratory analysis of the Chang’E-5 returned samples also provide critical clues to the possible sources of these hydroxyl contents. Much less agglutinate glass contents suggest a weak contribution of solar wind implantation. Besides, the apatite present in the samples can provide hydroxyl contents in the range of 0 to 179 ± 13 ppm, which shows compelling evidence that, the hydroxyl-containing apatite may be an important source for the excess hydroxyl observed at this young mare region.

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