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Helium is the second lightest and most abundant chemical element in the universe, if we stick to ordinary matter. It is only surpassed in this classification by hydrogen. This noble gas accounts for between 24 and 26% of the total mass of stars, which are also responsible for manufacturing it. fusing hydrogen nuclei inside through the reactions of nuclear fusion that they carry out naturally, and which we talk to you about in quite some depth in the article that we dedicate to the life of the stars.
Still, most of the helium in the universe was not made by stars: it was produced by the Big Bang, which is why scientists refer to it as “primordial helium.” But the most curious thing is that, despite how abundant it is in the universe, it is scarce on Earth. Its great lightness caused most of the helium contained in the cloud of dust and gas from which our planet was formed to escape gravitational confinement.
Be that as it may, the real protagonist of this article is not the normal helium that we have all heard about; It is helium-3, an isotope that may play a crucial role in nuclear fusion reactions that will possibly help us solve forever our energy problems. And also in other areas, such as, for example, in dilution cooling systems that use superconducting quantum computersas well as other emerging technologies.
Interlune plans to test the extraction of lunar helium-3 in 2027
Most of the helium that we can find in the universe has taken the form of an isotope known as helium-4, which is characterized by having two protons and two neutrons in its nucleus. Although, as we have seen, most of it was lost during the formation of the Earth, this gas can also arise as a result of natural radioactive decay of heavier chemical elements, such as uranium, radium or thorium, which are relatively scarce on our planet.
The only difference between helium-4 and helium-3 is that the latter isotope has one less neutron in its nucleus. That’s all. We know that helium-4 nuclei have two protons and two neutrons, so helium-3 nuclei will have two protons and a single neutron. It may seem like an irrelevant difference, but it is not. It is a very important difference because the physicochemical properties of the element vary as a consequence of their lower atomic mass. And, in the case of these two isotopes of helium, their behavior also changes from the point of view of quantum mechanics.
The solar wind spreads helium-3 throughout the solar system and beyond, causing it to reach surrounding planets in relatively large quantities.
The bad news is that if helium-4 is relatively scarce on Earth, helium-3 is even more so. Stars, like our Sun, produce it in large quantities as a result of nuclear fusion reactions between hydrogen nuclei that occur when they are in the main sequence stage during which they burn most of their fuel. Once created, the solar wind spreads helium-3 throughout the solar system and even beyond, causing it to reach surrounding planets in relatively large quantities.
The reason why this gas hardly accumulates on Earth is that our planet has a double protective shield: the atmosphere and the Earth’s magnetic field. These two barriers represent a very effective defense against the solar wind and cosmic radiation, which reaches the atmosphere mainly in the form of protons and high-energy alpha particles. The Moon, unlike the Earth, has no atmosphere, so it lacks this protective shield. Additionally, its magnetic field is much weaker than Earth’s and is not dipolar.
The terrestrial, on the other hand, can be approximated to a magnetic dipole, so the magnetic field lines are directed from the north pole to the south pole. All this causes the surface of the Moon to be much more exposed to cosmic rays and the solar wind than the surface of the Earth, causing very significant quantities of helium-3 transported by the solar wind to accumulate there, which is deposited in rocks and lunar dust, a few meters deep.
Up to a million tons of regolith need to be processed to obtain a single kilogram of helium-3
The first challenge that humanity will have to solve to appropriate the helium-3 accumulated on the Moon is none other than the processing of lunar regolithwhich is the loose layer of soil and rock fragments that covers the surface of the satellite. Interlune, a company founded in Seattle (USA) in 2020, plans to extract the regolith and process it using compact harvesting robots that, according to this company, are very efficient.
The problem is that lunar dust is very abrasive, and, in addition, up to a million tons of regolith must be processed to obtain a single kilogram of helium-3. Even so, this company plans to test the extraction of this isotope with a lunar mission in 2027, and in 2029 it intends to build a pilot plant on the Moon. It sounds good, but a priori these dates seem excessively optimistic. Additionally, it is still unclear how much it will cost to transport lunar helium-3 to Earth using space vehicles. Be that as it may, we can be sure that it will not be easy or cheap to do so.
Image | Pixabay
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