China’s Chang’E-5 lunar lander has made the first in-situ detection of water on the surface of the Moon, providing crucial context for the samples it returned to Earth. This mission landed on December 1, 2020, and returned samples later that same month (December 17, 2020).
Using its Lunar Mineralogical Spectrometer, Chang’E-5 collected reflectance spectra in the 0.48−3.2 micrometer wavelength range from its surroundings at the landing site in the Northern Oceanus Procellarum on the nearside of the Moon. Water (in the form of OH or H2O) exhibits a strong absorption at 2.85 micrometers. This was used by scientists to calculate the abundance of water in regolith (soil) at the landing site, as well as a light-toned rock near the lander that authors believe may be from a different geological unit.
The derived water contents of the regolith at the landing site varied from nearly undetectable to approximately 120 parts per million (ppm). Most of the measurements were below the detection limit, in agreement with measurements on Apollo regolith samples and orbital observations, with two data points at the higher water contents. These higher water contents were argued to result from the implantation of solar wind (mostly hydrogen), which was fortuitously not removed from these areas by the lander’s exhaust to reveal the dryer regolith underneath. These low water contents in the lunar regolith may suggest either that the lunar mantle is very dry or that there has been substantial volatile loss at the landing site. In contrast, the light-toned rock showed a water content up to 180 ppm, which may imply an additional source from the lunar interior.
“Our results provide the field geological context for the [already] returned samples and establish the relationship between the in-situ measurements and laboratory analyses of the returned samples,” writes Honglei Lin (Chinese Academy of Sciences) in the recent publication in Science Advances. READ MORE