Lunar exploration is undergoing a renaissance. Dozens of missions, organized by multiple space agencies—and increasingly by commercial companies—are set to visit the Moon by the end of this decade. Most of these will involve small robotic spacecraft, but NASA’s ambitious Artemis program aims to return humans to the lunar surface by the middle of the decade.

There are various reasons for all this activity, including geopolitical posturing and the search for lunar resources, such as water-ice at the lunar poles, which can be extracted and turned into hydrogen and oxygen propellant for rockets. However, science is also sure to be a major beneficiary.

The Moon still has much to tell us about the origin and evolution of the Solar System. It also has scientific value as a platform for observational astronomy. //

Several types of astronomy would benefit. The most obvious is radio astronomy, which can be conducted from the side of the Moon that always faces away from Earth—the far side.

The lunar far side is permanently shielded from the radio signals generated by humans on Earth. During the lunar night, it is also protected from the Sun. These characteristics make it probably the most “radio-quiet” location in the whole solar system, as no other planet or moon has a side that permanently faces away from the Earth. It is, therefore, ideally suited for radio astronomy. //

At that time, most of the matter in the Universe, excluding the mysterious dark matter, was in the form of neutral hydrogen atoms. These emit and absorb radiation with a characteristic wavelength of 21 cm. Radio astronomers have been using this property to study hydrogen clouds in our own galaxy—the Milky Way—since the 1950s.

Because the Universe is constantly expanding, the 21 cm signal generated by hydrogen in the early Universe has been shifted to much longer wavelengths. As a result, hydrogen from the cosmic “dark ages” will appear to us with wavelengths greater than 10 m. The lunar far side may be the only place where we can study this. //

Moreover, there are craters at the lunar poles that receive no sunlight. Telescopes that observe the Universe at infrared wavelengths are very sensitive to heat and therefore have to operate at low temperatures. JWST, for example, needs a huge sun shield to protect it from the sun’s rays. On the Moon, a natural crater rim could provide this shielding for free. //

But there is also a tension here: human activities on the lunar far side may create unwanted radio interference, and plans to extract water-ice from shadowed craters might make it difficult for those same craters to be used for astronomy. As my colleagues and I recently argued, we will need to ensure that lunar locations that are uniquely valuable for astronomy are protected in this new age of lunar exploration.