The quest for signs of advanced extraterrestrial civilizations, or technosignatures, has taken an intriguing turn. A recent paper by Oxford astrophysicist Brian C. Lacki proposes that the best place to search for evidence of alien megastructures may not be in distant star systems, but rather in the dust of our own Moon.
The Longevity of Civilizations
The search for technosignatures is often framed by the Drake equation, which estimates the number of technological civilizations in the Milky Way. A significant variable in this equation is the “longevity” of a civilization, which refers to the duration during which it produces detectable signals. Lacki emphasizes that the probability of overlapping with an active civilization is low, suggesting that we are more likely to discover the remnants of a “dead” civilization.
Passive Technosignatures
Traditionally, the Search for Extraterrestrial Intelligence (SETI) has focused on detecting passive signals such as radio waves. However, the window for sending such signals from Earth has been relatively short—approximately 100 years. As our communication technology evolves, many of our earlier broadcasts are being phased out. Thus, Lacki argues for the search for passive technosignatures, which could include relics that require no maintenance and can persist for billions of years.
Types of Passive Signatures
Lacki categorizes potential passive technosignatures into three types: diffusers, occulters, and glinters. Occulters would exhibit unnatural dimming patterns, similar to transiting exoplanets. Glinters would involve massive mirrors reflecting starlight, appearing as anomalous lens flares. Diffusers would scatter light isotropically, producing faint signals with unusual colors or polarizations. While these systems are inherently passive, their initial construction would necessitate some maintenance.
Moon Dust as a Repository
As civilizations evolve, their megastructures may eventually degrade into what Lacki terms “technograins.” These remnants could be propelled out of their host solar systems by solar winds, allowing them to drift through the galaxy. Our solar system, in its orbit around the Milky Way, encounters interstellar material, which may include pulverized technosignatures. The Moon, being an inactive body, could preserve these remnants for billions of years.
Ultimately, Lacki’s paper suggests that rather than relying solely on advanced space telescopes, we might find evidence of extraterrestrial intelligence by analyzing lunar regolith. Discovering such remnants would profoundly alter our understanding of cosmic history and the potential for intelligent life beyond Earth.
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