For a long time, it was assumed that the inside of the moon is bone-dry, as all volatile substances must have been lost during its formation history. But this assumption contradicted already a study from the year 2008: A research team of the Brown University in Providence discovered traces of water in Glaseinschlüssen in volcanic moon rock, which had brought back the Apollo 15 and 17 missions from the moon. In 2011, another study of tiny crystalline structures in these inclusions showed that they actually contained similar amounts of water as some basalt rocks on Earth. This indicated that at least parts of the moon mantle have similar bound water as comparable formations on earth.
"The question remained whether the Apollo missions' samples generally represented the characteristics of the Moon's interior, or perhaps coincidentally came from unusually water-rich regions, " says Ralph Milliken of Brown University. Looking through the lunar orbit, he and his colleagues have tried to clarify this question. They used data from the orbital spectrometer aboard the Indian probe Chandrayaan-1. By analyzing which wavelengths of light are absorbed or reflected by the lunar surface, scientists were able to draw conclusions about the minerals and compounds present there. As a reference material they used the samples of the Apollo missions.
The evaluations revealed: In almost all volcanic deposits of the moon, including the area of the landing sites of Apollo 15 and 17, the researchers found evidence of the presence of hydrous volcanic rocks. "The distribution of these deposits is the sticking point, " says Milliken. "They are everywhere - so the Apollo samples were not an unusual case. The volcanic deposits seem to be generally rich in water, suggesting that the same is true for the mantle of the moon, "the researcher said.
Results with scientific and practical benefits
As he and his colleagues emphasize, these results now raise interesting questions about the history of our satellite. It is believed that the moon was born with a bang: In the early days of the solar system, a Mars-large celestial body slammed on the young earth. From the ruins of this collision then formed the moon - it consists of earthly material and substance of the cosmic bolide. In this scenario, it seems unlikely that the heat of impact could have allowed water to form on the moon. "However, the current evidence suggests that somehow survived water or that it came to the moon shortly after the impact of asteroids or comets, before he has completely solidified, " says co-author Shuai Li. The exact origin of the water inside the moon is still an open question. "Display
In addition to the scientific importance, the results could also have practical benefits, say the scientists. They explain that while the volcanic glass inclusions do not contain much water - only about 0.05% by weight - there are so many of them that it could be worth the effort of producing water. Until now, shady regions on the lunar poles have been considered as cheap landing sites for moon missions, because there could be water ice. The volcanic deposits, however, there are also in places that could be much more accessible, the researchers say. "Ways to bring less water from the earth, are in great demand. Our results now suggest a new alternative, "said Li.
Original work of the researchers:
- Nature Geoscience, doi: 10.1038 / ngeo2993