Though the moon has been watching us stoically for billions of years, there are still plenty
of things we don’t know about it. We don’t really know for sure how it formed, where it came from,
and we especially know very little about its dark side. What mysteries are waiting
to be solved on this hidden hemisphere? This is Unveiled, and today we’re answering
the extraordinary question: what really happens on the dark side of the moon?
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Firstly, the name “dark side of the moon” is actually inaccurate,
despite being widely popularized by Pink Floyd’s most famous and influential album.
The name scientists use for the moon’s other hemisphere is “FAR side of the moon”,
because it’s not any darker than the side we can actually see. Just like the near side,
it still gets plenty of sunlight. In fact, when Earth has a new moon, if you were in space on the
opposite side, you’d be seeing a full moon as the entire hemisphere would be illuminated by the sun.
But it’s still dark in a more abstract sense. It’s mysterious and still very unknown because
of how difficult it is to actually get there. Human eyes hadn’t seen the far
side of the moon at all until the Soviet Luna 3 probe photographed it in 1959, images that
remain distorted and difficult to parse. And it wasn’t until Apollo 8 almost a decade later
that humans saw it in person, a privilege that’s been afforded to very few even today.
When people first saw the far side of the moon, they were struck by how much more pockmarked it
was compared to the near side. The near side of the moon does have a lot of craters, but it also
has huge, gray regions called “lunar maria” or “mare”. These areas are so pronounced that
you can easily see them with the naked eye when you’re looking at the moon on an ordinary night,
and indeed, they were named thousands of years ago by the Romans who could see them just like
we can today. The name “mare” is actually Latin for “sea”, the same root that we get words like
“maritime” from. It was believed that these gray expanses were actual seas.
In a sense, this was correct, but not in the way that Romans thought;
the maria are huge fields of ancient lava, some dating back billions of years to the formation
of the Earth-Moon system. When the moon formed, the near side was exposed to heat from the Earth,
which was still extremely hot. This resulted in a thinner crust on the near side,
with more aluminum and calcium condensing in the atmosphere of the cooler far side.
And this is why the near side has fewer visible impact craters. It’s not that there were fewer
asteroid impacts, but that the near side has had more volcanic activity and those craters
are filled by volcanic flows. The far side’s thicker, less malleable crust has prevented maria,
so we can see billions of years’ worth of impact craters there. Though the maria are extremely old,
the moon is constantly getting barraged by meteors, just like Earth. In both cases,
most meteors are small, but there’s always the chance that there will be a large impact event.
But one popular theory about the far side of the moon isn’t about these many impact craters
at all. According to some, the far side of the moon is the best place in the solar system for
aliens to spy on us without being detected. The moon itself blocks radio waves, meaning that if
aliens were living there and producing radio signals, we wouldn’t be able to detect them.
Since the moon is so inhospitable, any race trying to survive there would have to be very advanced,
and so would almost certainly be using radio waves in some way or another. It's also totally
invisible to humans on Earth because of the way the moon is tidally locked. There is simply no way
we could ever see the far side of the moon from Earth without using a lot of complex equipment.
However, the same thing that makes it so difficult for us to detect alien life on the moon would also
make it very difficult for them to spy on us in the first place. So it wouldn’t necessarily
be a great base of operations. Still, this hasn’t stopped conspiracy theorists from
trying to find strange structures in images of the far side of the moon over the years,
going as far as to suggest there are “castles” and other buildings present on the surface.
In 2020 they claimed such structures were even visible in official images released by NASA.
Because the moon blocks radio signals, there’s only one way to communicate with objects on
the far side of the moon from Earth: a relay satellite. Currently, there is only one relay
satellite serving this function, the Chinese satellite Queqiao. Queqiao was designed to
be a relay between the Chang’e 4 lunar lander and Yutu-2 rover, which landed on the far side of the
moon in early 2019. Without Queqiao, we would have no way to get any of the data the rover
is sending back to Earth, and if we ever want to further explore the far side of the moon,
we would need more of these satellites. Otherwise, the people there would be utterly stranded with no
way to communicate with Earth, which obviously isn’t ideal. If aliens were hiding over there,
they would also need relay satellites to spy on us, if that’s what they’re doing.
But in that case, we should have been able to detect these satellites by now.
Satellites are notoriously difficult to hide, for multiple reasons, but the main reason is
simply that you can see them. Some satellites you don’t even need a telescope to spot, just a pair
of binoculars. During the Cold War, scientists spent years trying to develop satellites that
can’t be detected on radar to little avail. Even if you make them as camouflaged as possible, you
still have the problem of infrared radiation. They produce a lot of heat and this makes them very
easy to spot if you have specialist instruments. Admittedly, if aliens were living on the moon
and had spy satellites, they could feasibly have used technologies unknown to us to disguise them.
However, this simple act of blocking out radio communications may be a reason why it’s more
interesting to look at what DOESN’T happen on the far side of the moon,
rather than what does. Because it’s a radio dead zone that doesn’t get any radio signals
from Earth beyond the Queqiao satellite, it’s the perfect spot to build a radio telescope.
The idea of building a radio telescope on the moon has been floated many times over the years,
with NASA itself proposing such an idea as recently as 2020. This particular plan is called
the Lunar Crater Radio Telescope, or LCRT, and it would be built in an impact crater on the far
side of the moon. NASA plans to build the LCRT using rovers and other robots, so that we don’t
need to send a manned mission out there to undertake grueling, lunar construction work.
But it’s not exactly gotten off the ground yet. As of writing, it’s still in the proposal stage.
If we could get together the funding to put a radio telescope on the moon, there’s no
telling what we would be able to find, and we wouldn’t have to worry about Earth interference.
For instance, the famous Wow! Signal, detected in 1977, has widely been reported as potential
evidence of intelligent, alien life trying to communicate. But many have suggested that
the Wow! Signal didn’t come from outer space at all, but from somewhere on Earth. This isn’t a
popular theory and it is generally accepted that the Wow! Signal did come from space,
even if it’s unlikely that it was an alien communication. But it does go to show just
how tricky detecting alien radio signals is with so much white noise coming from Earth. By building
the LCRT or any other radio telescope on the far side of the moon, we’d be one step closer to
detecting aliens. The moon’s potential as an alien detector is one big reason why the SETI Institute
actually advocates against sending missions to the far side of the moon. For example, it
objected to China’s Chang’e 4 mission on the basis that it would create too much radio noise there.
The far side of the moon is the most unfamiliar part of our closest celestial neighbor, and
we still have a lot to learn about what goes on there. Perhaps one day in the future we could use
it to our advantage… but, until then, it’s a solar system location that’s relatively close to us, and
yet one that will remain shrouded in mystery to a certain degree. The theories are sure to continue,
and the intrigue is sure to remain, because that’s what really happens on the dark side of the moon.
What do you think? Is there anything we missed? Let us know in the comments, check out these other
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