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The hidden side of the Moon is an ideal place to listen to alien civilizations

They want to mount a radio telescope inside a crater on the ocular side of the Moon. Image credit: Saptarshi Bandyopadhyay / NASA JPL

Are we alone in the universe? It is a question whose answer – whether yes or no – philosophically and scientifically would shake our world to the core. To find out, scientists have long used powerful radio telescopes for the cosmos. The theory is that, like us, other intelligent species may be transmitting radio signals with the distinctly “unnatural” signature of a technological civilization.

But despite decades of attentive listening, we still don’t catch anything. Even in a recent survey of 10 million stars made by the radio telescope Murchison Widefield ArraY in Western Australia – one of the most extensive to date – scientists have found nothing of note.

Where is everyone?

There are many theories, but one possibility is that we just don’t look hard enough. Our galaxy, with its hundreds of billions of stars and countless planets, is a very big place. The scientists who conducted the Murchison survey said it was like searching a pool-sized area in the ocean. In our search for a needle, we may just need to sieve more straw.

But there is a problem.

Our own civilization’s ceaseless radio chatter—which, in theory at least, would be similar to the signals SETI’s searching for—is growing louder, making it much harder for scientists to filter out local noise. While researchers have techniques and software to remove human signals, some are suggesting a more radical solution. Might we escape the noise entirely?

The further from civilization you go—Australia’s outback or Chile’s Atacama desert—the more the chatter fades. And if you keep following this line of reasoning to its end, you’ll land in a place with the most profound silence of all: the far side of the moon.

It is no surprise, then, that scientists have been dreaming of an observatory on the moon for years. Equally not surprising is the fact that such an observatory does not yet exist.

But one recent article – written by researchers sponsored by Breakthrough Listen, Eric Michaud, Andrew Siemion, Jamie Drew and Pete Worden – advocate a SETI observatory (search for extraterrestrial intelligence) on the Moon or in lunar orbit. And, notably, they suggest that such a project is perhaps for the first time approaching feasibility.

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SETI on the far side

The hidden side of the Moon is an ideal place to look for radio signals from other civilizations for a number of reasons.

The first, as noted, is its exquisite radio silence. Astronomer Phillipe Zarka, quoted by the authors, said:

The hidden side of the Moon during the lunar night is the quietest place in our local universe.

And for radio signals of human origin, this is a permanent condition. The Moon is locked by gravity, so one side of it is always facing away from Earth.

How quiet is there?

According to the authors, a NASA orbiter in the early 1970s found that Earth’s radio noise decreased by one to three orders of magnitude when the satellite passed behind the moon. Simulations suggest that this effect would be even greater on the surface. lunar. One study found that near the Daedalus crater some radio signals from Earth would be reduced by up to 10 orders of magnitude (10 billion times). The only remaining radio interference from man would be from jeep probes and probes in other parts of the Solar System – of which there are, of course, much less than in Earth orbit.

In addition to an environment largely devoid of human radio interference, lunar nights last for two weeks, allowing extended viewing groups. And the cherry on top: an observatory on the Moon can detect wavelengths in parts of the radio spectrum that are blocked by the Earth’s ionosphere.

Together, these attributes make the Moon an exceptionally desirable destination for SETI – if you can, in fact, find out how to finance and build an observatory that takes advantage of them …

… There is no way to say when (or if) we will have a SETI observatory on the far side of the Moon, but the search for silence is a valid cause. It would be a shame to miss ET’s call simply because we can’t hear the phone.


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