Lunar exploration is experiencing a renaissance. Dozens of missions organized by various space agencies and increasingly commercial companies are poised 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 several reasons for all this activity, including geopolitics and the search for lunar resources that can be mined like water ice at the lunar poles and converted into hydrogen and oxygen for rockets. However, science would certainly benefit a lot as well. The moon has a lot to tell us (opens in new tab) about the origin and development of the solar system. It also has scientific value as a platform for astronomy observations.

The potential role of Earth’s natural satellite for astronomy was discussed at a meeting of the Royal Society earlier this year. The meeting itself was prompted in part by the now anticipated extended access to the lunar surface.

Advantages of the far side

Several types of astronomy would be useful. The most obvious is radio astronomy, which can be done on the reverse side of the Moon always facing the Earth. The far side of the Moon is permanently shielded from radio signals produced by humans on Earth. It is also protected from the sun on a moonlit night. These features make it perhaps the most “radio quiet” place in the entire solar system, because no other planet or moon has a side permanently facing away from Earth. Therefore, it is ideal for radio astronomy.

Radio waves are a form of electromagnetic energy, such as infrared, ultraviolet, and visible light waves. They are determined by different wavelengths in the electromagnetic spectrum. Radio waves with a wavelength greater than 15 m are blocked by the Earth’s ionosphere. However, radio waves of this wavelength reach the surface of the Moon unhindered. For astronomy, this is the last unexplored region of the electromagnetic spectrum and is best studied from the far side of the Moon.

Observing space at these wavelengths falls under the umbrella of “low frequency radio astronomy.” These wavelengths have the unique ability to probe the structure of the early universe, particularly the cosmic dark ages. – the period before the formation of the first galaxies. At that time, most of the matter in the universe was in the form of neutral hydrogen atoms, except for the mysterious dark matter. They emit and absorb radiation with a characteristic wavelength of 21 cm. Radio astronomers have used this property to study hydrogen clouds in our own galaxy, the Milky Way, since the 1950s.

As the universe continued to expand, the 21 cm signal produced by hydrogen in the early universe was shifted to much longer wavelengths. As a result, hydrogen from the cosmic “dark ages” will appear to us at wavelengths longer than 10 m, and the far side of the Moon may be the only place we can study it.

Presenting a good summary of the scientific basis at a recent meeting of the Royal Society, astronomer Jack Burns described the far side of the Moon as “a pristine, quiet platform for low-frequency observations of the dark ages of the early universe.” Space weather and magnetosphere associated with habitable exoplanets.” .

Signals from other stars

Another potential application of distant radio astronomy is trying to detect radio waves from charged particles trapped in the magnetic fields (magnetospheres) of planets orbiting other stars, Burns says.

This will help assess the extent to which these exoplanets can support life. Radio waves from the outer planets’ magnetospheres would likely have a wavelength of more than 100 m, so they would need a radio-quiet environment in space. Again, the far side of the Moon would be the best place.

A similar argument can be made for attempts to detect signals from intelligent aliens. And after discovering an unexplored part of the radio spectrum, there is also the opportunity to make accidental discoveries of new phenomena. We should learn about the potential of these observations when NASA’s LuSEE-Night mission lands on the far side of the Moon in 2025 or 2026.

crater depths

The moon also provides opportunities for other types of astronomy. Astronomers have extensive experience with optical and infrared telescopes operating in space, such as the Hubble Space Telescope and the James Webb Space Telescope (JWST). However, the stability of the lunar surface could be advantageous for such instruments.

There are also craters at the poles of the Moon that do not receive sunlight. Telescopes observing the universe in infrared radiation are very sensitive to heat and therefore have to operate at low temperatures. JWST, for example, needs a massive sun shield to protect it from the sun’s rays. On the Moon, the natural crater rim could provide this protection for free.

The Moon’s low gravity may also enable the construction of much larger telescopes (opens in a new tab) than is possible for free-flying satellites. These considerations led astronomer Jean-Pierre Maillard to suggest that the Moon could be the future of infrared astronomy.

The cool, stable environment of permanently shadowed craters could also have the advantages of detecting gravitational waves, “ripples” in space-time caused by processes such as exploding stars and colliding black holes.

In addition, the Moon has been bombarded by charged particles from the Sun – the solar wind – and galactic cosmic rays for billions of years. The lunar surface may contain many records of these processes. Examining these can provide insight into the evolution of both the Sun and the Milky Way.

For all these reasons, astronomy will benefit from the current renaissance of lunar exploration. As lunar exploration continues, astronomy in particular will benefit from infrastructure built on the Moon. This will include both transportation infrastructure (rockets, ground vehicles, and other vehicles) to access the surface, as well as humans and robots in the field to build and maintain astronomical instruments.

But there’s a tension here too: Human activity on the far side of the Moon could create unwanted radio interference, and plans to extract water ice from shadowy craters could make it difficult to use the same craters for astronomy. As my colleagues and I have discussed recently, we will need to ensure that areas on the Moon are protected, which are of unique value to astronomy in this new era of lunar exploration.