China’s Chang’e 5 lunar lander has sent back the first on-site evidence of water on the surface of the moon.
The moon had long been thought to be totally dry, but scientists have confirmed the presence of water on its surface just over a decade ago.
Until now their findings had been based on orbital observations but the latest study, published in Science Advances on Friday, said the lander had detected signs of water molecules (H2O) or a close chemical relative hydroxyl (OH).
“It’s like a ‘field trip’ out on the Moon, the first opportunity to detect signs of water at close range and high resolution on the lunar surface,” Lin Honglei, lead author of the study from the Institute of Geology and Geophysics at the Chinese Academy of Sciences, told China Science Daily.
Chang’e-5 sent back rock samples of the moon in late 2020 and since then the lander has been carrying out further observations, including an analysis of the characteristics of lunar water.
Most of the water in the lunar soil is thought to be the result of “solar wind” that drove hydrogen atoms onto the surface of the moon, where they reacted with oxygen in the surface minerals to form water and hydroxyl.
Chang’e 5’s lander used a mineralogical spectrometer to analyze the chemical composition of rocks and soil at the landing site and found a water concentration of fewer than 120 parts per million (ppm), or roughly equivalent to 120g water in one tonne, in the lunar soil.
In contrast, the water concentration in the rock was about 180 ppm, a difference the researchers said could be a result of the rock originating from below the surface where there may be an additional water source.
The study builds on years of previous research examining the presence of water on the moon. When the Apollo astronauts first returned from the moon in 1969, the satellite was thought to be completely dry.
It was not until 2007 when water molecules were first discovered in lunar rocks. In 2018, Nasa confirmed the presence of water ice in permanently shadowed craters around the moon’s poles and two years later announced that H20 was widely distributed across the lunar surface.
China is planning two further missions to the moon – Chang’e 6 and 7 starting in 2024 – to examine the content and distribution of lunar surface water at the same site, Lin Yangting, one of the study’s co-authors, said.