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“Space erosion” is the gradual erosion of unprotected planets, moons, and asteroids caused by solar wind, cosmic rays, micrometeorites, and larger meteors. Agglutination and solar wind are forms of spatial disturbance that affect the physical and optical properties of planetary surfaces. Helium-3, deposited on the sun-facing surface of the Moon by the solar wind, is considered an economic resource by the Russian and Chinese governments for second-generation nuclear fusion energy.
“Space erosion” refers to the slight erosion caused on unprotected planets, moons and asteroids from solar wind, cosmic rays, micrometeorites and larger meteors. Space weathering affects the physical and optical properties of the surfaces of planetary bodies, so understanding their specifics is important for interpreting remotely sensed data, such as space probe photographs of the solar system’s outer moons.
The first form of spatial alteration recognized is that of agglutination: tiny fragments of material that are vaporized by tiny micrometeorites and scattered on the surface. The agglutinated coated material appears black to the human eye due to the presence of nanophase iron. Agglutination is common, for example, in lunar soils, where it makes up 60 to 70% of mature lunar soils. Spatial agglutination and erosion are partly responsible for the dark appearance of the lunar maria. Because the average micrometeorite is tiny (only a few tens of nanometers in diameter), erosion occurs on very small surface levels, and only in the last couple of decades have we had microscopes powerful enough to probe the specifics of its structure.
Another form of spatial disturbance that occurs, in part on the Moon, where it has been studied, has to do with the solar wind. Over billions of years, the solar wind hitting the sun-facing surface of the Moon deposited light elements, most notably helium-3, which is thought to be a source of second-generation nuclear fusion energy. Helium-3 requires more energy to fuse than first-generation nuclear fusion fuels such as deuterium, but it also releases more energy. Just 20 tons of Helium-3 could fuel US energy needs, if we successfully develop a fusion reactor that can extract more energy from Helium-3 than is needed to fuse it.
The helium-3 on the Moon caused by space erosion is considered an economic resource by the Russian and Chinese governments. The Chinese government has cited helium-3 as the main reason for trying to reach the Moon, and a Russian energy company has set a goal of mining helium-3 on the Moon by 2020.
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