Credit: © NASA

The lunar inventory of 3He — the lighter, non-radioactive isotope of helium that has been suggested as a potential source of fusion fuel — is believed to be higher than on Earth. A new study quantifies the distribution and total amount of this isotope on the Moon's surface.

Wenzhe Fa and Ya-Qiu Jin from Fudan University in China1 simulate the solar wind flux distribution on the near and far sides of the moon — the main source of lunar 3He. They combine the results with estimates of the maturity of the lunar soil and the abundance of the mineral ilmenite, which are the two main determining factors for the retention of 3He in the surface soil. They also propose a remote sensing model to estimate the regolith layer thickness, which can address a major uncertainty in estimation of the lunar 3He inventory. Together with measured ground truth from the Apollo soil samples, the results suggest that the lunar maria — extensive volcanic plains on the Moon's surface — are likely to have the highest relative abundances of 3He as their high content of titanium dioxide suggests abundant ilmenite. The overall 3He content in the Moon's regolith is estimated to be around 650,000 tonnes, which is much more than the 20 tonnes previously suggested for Earth.

Whether 3He mined from the Moon will ever provide an alternative to fossil fuels remains unclear. But the fact that we can even attempt to quantify its abundance bears witness to our phenomenal acquisition of knowledge of the Moon, the solar system and the Universe over the 50 years since the launch of Sputnik — reason enough to celebrate humanity's first step into space.