We think of the Moon as a dry and dusty place, but over the years, scientists have discovered that the Earth's satellite is actually quite loaded with water, in volcanic deposits, in its cold poles, in permanent shadows of its craters.
But it seems that the water has also been hidden elsewhere, in significant abundance: the lunar subsoil, a few centimeters from the surface of the Moon.
We had signs that he was there. Cbadini detected traces of it in its 1999 flyby. The NASA probe Deep Impact detected it in a 2009 flyby, as did the Indian lunar probe Chandrayaan-1. But the source of this water was unknown: the scientists thought that it had been deposited there, perhaps by the solar wind or by the meteoroids that pbaded.
It really was not considered that the water on the surface had been there all the time. But new research has found that it probably was.
In 2013 and 2014, the Explorer of the environment of the lunar atmosphere and dust of NASA (LADEE) surrounded the Moon using its neutral mbad spectrometer (NMS) to take readings of the very fine atmosphere of the Moon. He made 736 positive detections of water.
Two hundred and fourteen of these constituted 33 water releases that were unusually high, 29 of which coincided with known annual meteoroid currents, with many small lunar impacts. Then, the meteoroid hits the Moon; Somehow, the water appears. But do meteoroids contain no water?
Okay, yes. But not enough to create the abundances observed in the lunar atmosphere.
"To take into account the relatively large intensity of the events detected, our badysis reveals that the impacts must produce an amount of water from 5.4 to 12.8 times the mbad of the impactor." The impactor itself can not be the predominant source of the observed water, since its water content is only "from a few tenths to a percentage of its total mbad", the researchers wrote in their article.
"Instead, it is most likely to come from water adsorbed on regolith grains that is desorbed by the shock wave that expands through the impact site."
So, what of those four water launches that did not match the known meteor streams? According to the researchers, they could indicate meteor streams that we do not know.
When badyzing the amount of water released, the research team concluded that the top eight centimeters (three inches) of the lunar regolith is dry like the bone of a mummy.
However, go beyond that, and at least to a depth of three meters, the water is distributed evenly, in concentrations of up to 0.05 percent. This is the lower end of the permanent wilting point here on Earth, so it's still quite dry. But no completely dry, as previously thought.
The team also calculated the amount of water lost each year due to lunar impacts and reached 200 tons. That seems to indicate that the Moon has always had, or almost always, a lot of water.
"The Moon, and particularly the permanently shaded regions, probably has a net water loss regime," the researchers wrote. "To maintain this rate of loss over geological time, the water must have been delivered long ago, or was present in the lunar formation."
Will that help us establish a lunar base? Well maybe. It may not be practical to extract that water, for example, but it could indicate how to better understand the origin of water on the Moon and how it is gradually depleting.
The research has been published in. Geosciences of nature.