The Far Side of the Moon Is an Ideal Place to Listen For Alien Civilizations

Singularity Hub Daily

Are we alone in the universe? It’s a question whose answer—whether it’s yes or no—would philosophically and scientifically rock our world to the core. To find out, scientists have long been turning powerful radio telescopes to the cosmos. The theory is that, like us, other intelligent species are perhaps broadcasting radio signals with the distinctly “unnatural” signature of a technological civilization. But despite decades of intent listening, we’ve yet to pick anything up. Even in a recent survey of 10 million stars by the Murchison Widefield Array radio telescope in Western Australia—one of the most extensive to date—scientists found nothing of note. Where is everyone? Theories abound, but one possibility is we simply haven’t looked enough. Our galaxy, with its hundreds of billions of stars and countless planets, is a very big place. The scientists conducting the Murchison survey said it was like searching an area the size of a swimming pool in the ocean. In our search for a needle, maybe we just need to sift more straw. But there’s 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’s no surprise, then, that scientists have been dreaming of an observatory on the moon for years. Equally unsurprising is the fact no such observatory yet exists. But a recent paper—written by Breakthrough Listen sponsored researchers Eric Michaud, Andrew Siemion, Jamie Drew, and Pete Worden—makes the case for a SETI (search for extraterrestrial intelligence) observatory on the moon or in lunar orbit. And notably, they suggest that such a project is, perhaps, for the first time approaching feasibility. SETI on the Far Side The far side of the moon is an ideal place to search for radio signals from other civilizations for a few reasons. The first, as noted, is its exquisite radio silence. Astronomer Phillipe Zarka, quoted by the authors, says, “The far side of the moon during the lunar night is the most radio-quiet place in our local universe.” And for radio signals of human origin, this is a permanent condition. The moon is tidally locked, so the far side always faces away from Earth. How quiet is quiet? According to the authors, an early-1970s NASA orbiter found radio noise from Earth declined by one to three orders of magnitude as the satellite passed behind the moon. Simulations suggest this effect would be even greater on the lunar surface. One study found that near the crater Daedalus some radio signals from Earth would be reduced by as much as 10 orders of magnitude (10 billion-fold). The only remaining radio interference of human origin would be from rovers and probes elsewhere in the Solar System—of which there are, of course, far fewer than in Earth orbit. Added to an environment largely devoid of human radio interference, lunar nights last two weeks, allowing for extended viewing parties. And the cherry on top: An observatory on the moon could detect wavelengths in parts of the radio spectrum that are blocked by Earth’s ionosphere. Together, these attributes make the moon a uniquely desirable destination for SETI—if you can, in fact, figure out how to fund and build an observatory that takes advantage of them. The paper outlines two options. A Lunar Arecibo The easiest route would be to place a telescope in lunar orbit. The orbiter would scan the sky for signals from behind the moon—taking advantage of the far side’s ra...