An article published in the journal “Nature Communications” describes a research about the water on the Moon and concluded that it was brought mostly by asteroids that struck it between 4.5 and 4.3 billion years ago. Until now, scientists generally thought that water was transported by comets but according to the international team led by Jessica Barnes of the British Open University things are different.
The problem of water on the Moon is complex and had several twists over the decades. The Apollo missions brought back to Earth a number of rocks from the Moon but initially it looked like they were totally devoid of water. Subsequent analysis techniques allowed to study them better finding inside them small amounts of water. This led scientists to wonder where it came from and the most plausible answer were comets.
In the course of this new research the chemical and isotopic composition of the lunar volatile materials were compared with those of the materials found in comets and meteorites. The amount of water that might have arrived on the Moon from comets and asteroids was calculated and the result is that more than 80% came from asteroids known as carbonaceous chondrites.
This type of asteroid consists of materials that remained in the same state of a few billion years ago, at the beginning of the solar system’s history. These are materials that include carbon and even organic compounds, including amino acids. When the Moon was still forming following an impact of a planetoid with the primordial Earth, those asteroids bombarded it for a long time, at least several tens of millions of years.
At the time the surface of the Moon was a kind of magma ocean and the water brought by asteroids mixex up with the various minerals. When the rocks cooled down and solidified, that water remained trapped inside them, even in the deeper layers. According to the researchers comets have contributed only a small fraction of that water because the water in comets contains a greater amount of deuterium compared to that found on Earth, on the Moon or in the asteroids.
This isn’t the first research to support the theory of water brought to the Moon by asteroids: in September 2015 an article published in the journal “Planetary and Space Science” described a research on this topic. In that case, however, that theory was supported by computer simulations, instead this time there are direct analyzes of the water existing on the Moon.
The doubt is that water may have been brought more recently, when on the Moon there was still volcanic activity capable of melting the rocks and then to mix the water with them. The research will continue, also because it’s the water present on Earth has likely the same origin.