China's lunar lander Chang'e-5, which had earlier confirmed the presence of water on the Moon, has now determined its source on the lunar surface.
In 2020, Chang'e-5 delivered the first real-time, on-site definitive confirmation of water signal in the 11 basalt rocks and soil samples via on-board spectral analysis. Again in 2021, the finding was validated through laboratory analysis of eight samples the lander returned in 2021.
Now, the Chang'E-5 team has determined where the water came from and published their results in the journal Nature Communications.
"For the first time in the world, the results of laboratory analysis of lunar return samples and spectral data from in-situ lunar surface surveys were used jointly to examine the presence, form and amount of 'water' in lunar samples," said LI Chunlai from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC).A
"The results accurately answer the question of the distribution characteristics and source of water in the Chang'e-5 landing zone and provide a ground truth for the interpretation and estimation of water signals in remote sensing survey data," Chunlai added.
Chang'e-5 did not observe lunar rivers or springs; rather the lander identified, on average, 30 hydroxyl parts per million in rocks and soil on the Moon's surface.
The samples were collected during the hottest part of the Moon's day, at temperatures nearing 200 degrees Fahrenheit, when the surface would be at its driest. The timing also coincides with low solar winds, which can contribute to hydration at high enough power.
The team found hydroxyl to originate from two different sources.
A small portion appeared in glassy material made by solar winds interfering with the lunar surface, just as it did in an Apollo 11 sample collected in 1971 and tested in the early 2000s.
But the Chang'e-5 sample only contained about a third the amount of solar wind-generated, hydroxyl-containing glass as the Apollo sample.
This suggests that the solar wind still contributed, although weakly, to the hydroxyl contents observed in the Chang'e-5 landing site. The bulk of the hydroxyl in the Chang'E-5 samples was contained in apatite, a crystalline, phosphate-rich mineral naturally found to be on the Moon, as well as Earth.
Launched on November 23, 2020, Chang'e 5 is China's first lunar sample-return mission and the fifth lunar exploration mission of the Chinese Lunar Exploration Programme. It landed on the Moon on December 1, 2020, in the Northern Oceanus Procellarum near a huge volcanic complex, Mons Rumker.