Keeping an eye on the far side of the moon

When Canadian astronaut Jeremy Hansen travels beyond the moon on Artemis 2, part of his job will involve observing the far side of the moon, which is not visible from Earth. At the same time, scientists back on Earth will also be watching carefully, because they plan to eventually send telescopes and robots there to peer into deep space.

Our moon is literally two-faced. Since it is gravitationally locked to the Earth, it always keeps one side facing towards our planet and the other side facing outwards to deep space. While the far side is sometimes called the dark side, this is a misconception. It gets as much sunlight as the side facing Earth.

The far side of the moon is a much rougher, crater-saturated surface than the near side, which has large flat plains, called "Maria" which is the Latin word for seas. It is also a very quiet place, sheltered from all the artificial radio noise that comes from the Earth, which is why astronomers are so interested in it as a location for their radio telescopes.

The only way to see the far side of the moon is by spacecraft, so Hansen will have the rare opportunity to see sights few humans have seen with the naked eye since the Apollo era. In fact, he will see more than those early pioneers, because the Artemis flight path will take him 7,500 kilometres beyond the moon, so the entire globe will come into view.

Apollo astronauts orbited very close to the surface, so they only saw the equatorial regions. 

In addition, Hansen will see the whole Earth alongside the moon at the same time, a perspective never before seen by human eyes.

During their flyby of the moon, the Artemis crew will be peering out the windows making detailed observations of the lunar surface because the human eye can pick out subtle details such as differences in colours or shades of grey that cameras could miss. Those differences reflect various ground conditions, such as the amount of dust or roughness of the surface that could affect a landing spacecraft. 

One of the proposed missions to the far side is the Japanese TSUKUYOMI, or the Lunar Meter Wave Telescope, that will place the first of an array of radio dishes on the lunar far side in an attempt to look back to the earliest days of the universe known as the dark ages. 

About 400,000 years after the big bang, a time before stars and galaxies were born, there was a period when the universe was made mostly of neutral hydrogen gas that did not give off light, hence the term dark ages. However, the gas did radiate very faint radio signals that should be detectable by ultra sensitive instruments on the moon. 

Signals from the dark age could also unravel the mystery of how dark matter, which dominates matter in the universe today, affected the evolution of the early universe, perhaps directing it to develop stars, galaxies and planets.

The first TSUKUYOMI prototype is proposed to land near the south pole of the moon in 2027 to 2028, with more antennae aimed at the far side in the 2030s. These will be joined by another robotic radio observatory called LuSEE Night from the University of Boulder Colorado, which aims to launch this year, and a NASA robot called Farside Seismic Suite that will record moonquakes, scheduled to launch in 2027.

There are also other plans for lunar observatories by both NASA and ESA that are in the early stages of development.

While the human missions to the moon will focus on building a colony and searching for water ice at the south pole, their landing sites will always have the Earth on the horizon for communication purposes.

On the other side of the moon, completely hidden from view, will be a plethora of robots silently peering out to the edge of the universe and back to the beginning of time to find out how it all began.