Less than two years ago, China took both small and large steps towards its goal of becoming a space power. For the first time, the Asian giant has managed to send a robotic spacecraft to the Oceanus Procellarum, the ocean of storms, a huge dark spot on the Moon visible to the naked eye from the Earth where they are located, according to those responsible for the Chinese. space program. , the youngest terrains on our satellite. The catheter Chang’e 5 Upon landing near Mount Rümker, a 70-kilometre-long mass that rises more than a kilometer above the horizon, he used a robotic arm to collect samples, package them and send them to the orbiter hovering over the moon. From there they were sent back to Earth. And all this in a single lunar day, about 14 Earth days.
Analysis of these samples, the first collected from the Moon since the Soviet mission moon 24 in 1976, today it is a surprise. China believes it has solved one of the Moon’s biggest mysteries: where does the water it contains come from?
The Moon likely formed when a planet the size of Mars collided with Earth more than 4 billion years ago. The cataclysm caused a piece of Earth to be ripped off and completely covered in molten rock by the violence of the impact. The temperatures must have been so hellish that all the water must have evaporated forever.
However, in recent years, several robotic missions and ground-based telescopes have confirmed that the Moon continues to store water; and not drops, but tons in the form of ice. Much of it is in the perpetual shadow areas of the poles, where the sun never reaches. And these unexplored regions, especially those at the South Pole, have become where the first manned missions to the satellite will land in more than 50 years. They go there precisely because there is water, and with it possible sustenance for the colonists and raw material for rocket fuel with which, one day, they will reach Mars.
Until now, it was not known where that icy water came from. Other space probes have pointed out that it also exists in the illuminated areas of the satellite without knowing once again how it got there, perhaps on board asteroids or in some reserve not detected so far.
In a study published today, scientists from the Chinese National Academy of Sciences (CAS), in collaboration with two European researchers, guarantee that the key to the origin of water on the Moon lies in the samples sent to Earth by the Chang’e 5 northwest of the satellite. These contain impact glass, tiny grains of different colors that likely formed at high temperatures after meteorites collided. These glasses collected by the Chinese probe contain small amounts of water, according to the study, published in the specialized magazine nature geoscience.
Sen Hu, from the ANC’s Laboratory of Planetary Physics, explains that the water content in the crystals is about 2,000 parts per million, or about 2,000 grams for every ton of soil. “On the Moon, meteorite impacts are very frequent and occur throughout the entire satellite, with which the glass is distributed throughout its geography, from the equator to the polar regions”. The precious element may be in its molecular variant, with two atoms of hydrogen and one of oxygen, although the so-called hydroxyl is probably more abundant, with one atom of hydrogen and one of oxygen, explains Hu.
The researchers estimated the total amount of H₂O on the entire Moon stored in this way: about 270 billion tons. This is a huge reserve compared to other estimates. In 2010, for example, a NASA radar on board the Indian probe chandrayaan He estimated that at the North Pole there were about 600 million tons.
The Chinese samples are about a billion years younger than those collected by astronauts in the US Apollo program and the Soviet Union’s robotic missions. The latest analyzes show that these crystals have been forming for the last 2 billion years, with peaks in production coinciding with periods of intense meteorite bombardment, including 68 million years ago when another large meteorite hit Earth and wiped out the dinosaurs. ,
“The most interesting thing”, explains Hu, is that the water that is trapped in the lunar crystals was generated by the Sun. Analysis of the different types of hydrogen atoms in the samples suggests that the bombardment of charged particles from the sun, called the solar wind, and which contain positively charged hydrogen atoms, penetrate the glasses and combine with the oxygen already present. When the temperature is high enough due to solar radiation, these crystals can also release some of their H₂O cargo. “These crystals are responsible for the water cycle on the Moon”, summarizes the Chinese scientist.
With a view to future manned missions, “this could be an alternative source of water”, acknowledges the researcher. “The way to extract it would be to collect the lunar soil, heat it in an oven at 100 degrees and capture the resulting steam”, he details.
It might sound crazy, but Europa is sending a robotic mission to the Moon called Prospect to do just that as part of an experiment. A probe will drill into the lunar soil, collect samples and heat them up to 100 degrees to study the volatile compounds present, including water vapour, explains James Carpenter, head of planetary sciences at the European Space Agency (ESA), to this newspaper. “This project, which we will launch in 2026, can shed light on whether there is water trapped in the moon’s minerals,” he points out.
The new China-led study provides “an important demonstration that water is trapped in lunar crystals scattered across the surface,” Carpenter said. But the amount of this material is very small, mind you, so to get interesting amounts on manned missions, a lot of lunar soil would have to be processed. “These cups are probably not an exploitable water reserve,” he says.
What this work provides is clear evidence of the water cycle on the satellite, including the possible origin of frozen reserves at the poles. The Moon’s atmosphere is so thin that molecules suspended in it never interact. That way, when the sun hits the glass grains, it releases water vapor and is ejected “in a ballistic trajectory,” like a cannonball, explains Carpenter. “Water tends to stay longer in the coldest and darkest places”, which would explain why it accumulated in the form of ice at both poles, he points out.
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