\n<\/p>\n
Imagine an alien civilization that runs on dazzling technologies far more advanced than our own. Picture city-size starships, planet-wide mines or swarms of solar panels that harvest energy directly from a star.<\/p>\n
As these aliens go about their otherworldly business, the erosive forces of space wear down their infrastructure, loosening tiny bits of debris that detach and drift into the cosmos. If the civilization collapses, its remains degrade even faster. Clouds of particles might be unleashed into the galaxy, akin to the microplastics in Earth\u2019s oceans, sprinkling countless worlds with the detritus of an extraterrestrial society.<\/p>\n
Some of these particles, if they exist, may have even wafted through our solar system, perhaps settling on the surface of the moon, proposes a team of scientists focused on the search for extraterrestrial intelligence, or SETI. In their provocative study, which is in peer review for the <\/em>International Journal of Astrobiology, they suggest that searching for these microscopic remnants in lunar soil could resolve one of humanity\u2019s great questions: Are we alone in the universe?<\/p>\n \u201cIf any other technological civilization has ever existed in our galaxy, it\u2019s not an unreasonable hypothesis to think that particles of them are on the moon in some quantity,\u201d said Lewis Pinault, an affiliate scientist at the SETI Institute in Mountain View, Calif. and a researcher at Birkbeck College, University of London , who led the research.<\/p>\n<\/div>\n<\/div>\n In the study, the team showed how alien infrastructure might weather and erode into tiny particles and modeled how they would be dispersed through the galaxy. This process is already well observed here on Earth: Satellites, for example, shed microscopic material into space.<\/p>\n Sofia Sheikh, a scientist at the SETI Institute who studies hypothetical alien technologies known as \u201ctechnosignatures,\u201d described the team\u2019s idea as \u201ca creative and worthwhile avenue.\u201d She said that is especially true in the context of renewed interest in the moon from Artemis, a NASA program that aims to return astronauts to the moon\u2019s surface.<\/p>\n \u201cWe know on Earth that time and entropy take their toll on everything that humans make,\u201d wrote Dr. Sheikh, who was not involved in the study, \u201cand there\u2019s a lot more to explore in how the breakdown of technological artifacts can be applied to SETI searches.\u201d<\/p>\n<\/div>\n<\/div>\n Dr. Pinault and his colleagues modeled the possible trajectories of the particles through the galaxy, showing how they might intersect with our solar system over time. They speculate that some particles might survive impacts with the moon, leaving traces of alien societies that may have already gone extinct.<\/p>\n<\/div>\n<\/div>\n \u201cIf you concede that looking for alien intelligences is a legitimate part of science, which clearly it is, then looking for the technological products \u2014 a.k.a artifacts of these intelligences \u2014 ought to be just as scientifically valid as looking for their radio emissions,\u201d said Ian Crawford, a professor of planetary science at <\/strong>Birkbeck College, University of London and a co-author on the study.<\/p>\n The idea was inspired in part by the Ukrainian researcher Alexey V. Arkhipov, who in the 1990s pioneered the idea that the moon could be a collection site for alien artifacts. But in that era, the search for alien life was largely relegated to the fringes of academic research, and Dr. Arkhipov\u2019s research didn\u2019t gain much traction at the time.<\/p>\n Dr. Pinault and his colleagues have resurrected the concept and trained their focus on particles on the small scale of microns, comparable in size to a single bacterium. In a nod to Dr. Arkhipov\u2019s work, the scientists named their hypothetical specks \u201cArkhipov particles\u201d in the study.<\/p>\n Each star could have had multiple civilizations that were generating debris, Dr. Pinault said. He added that aliens \u201cmay have become starfarers who are developing similar technologies around each star system that they go to, so the potential of there being quite a bit of interesting debris in the galaxy is pretty high.\u201d<\/p>\n The researchers also considered the possibility that aliens might have dispatched microscopic machines for surveillance purposes or other types of active missions. They called these operational objects \u201cBracewell particles\u201d after the physicist Ronald Bracewell, who proposed the idea of autonomous alien probes in the 1960s.<\/p>\n<\/div>\n<\/div>\n Jason Wright, a professor of astronomy and astrophysics at Penn State and a SETI researcher, called the preprint \u201cimpressive\u201d and \u201cextremely thorough\u201d and said the approach was worth a shot.<\/p>\n \u201cThey\u2019ve revived what is actually a pretty obscure idea and shown that it\u2019s plausible,\u201d said Dr. Wright, who was not involved in the work.<\/p>\n<\/div>\n<\/div>\n To test their hypothesis, the scientists propose sending a mission to the surface of the moon to sift through about a cubic meter (35 cubic feet) of soil as a starting point \u2014 a tall ask. Specialized instruments would then comb through the soil searching for artificial particles, perhaps by screening for metals and other manufactured substances.<\/p>\n Dr. Pinault has already developed models designed to search for larger artificial objects on the moon, such as the unlocated remains of the Soviet lander Luna 9. Similar models could also be trained to detect tiny grains that might have an artificial origin.<\/p>\n<\/div>\n<\/div>\n Even if artificial grains were identified, there would be a high chance that they were of human origin. Many spacecraft parts have crashed into the moon over the decades, so it would not be surprising to find micron-scale debris from our own defunct missions. To determine whether a particle came from Earth or from some alien world, scientists would need to analyze the chemical fingerprint of the object.<\/p>\n Finding even one alien technosignature in one lunar sample is a long shot, Dr. Crawford said. But if one were found in the moon\u2019s dust \u2014 and confirmed to be genuinely alien, rather than rubbish from our own civilization \u2014 it would answer the tantalizing mystery of whether life exists beyond Earth.<\/p>\n \u201cThe chances of finding anything on the moon are so small,\u201d Dr. Crawford said, that \u201cthis would immediately imply that there must probably be lots and lots of them, at least in the history of the galaxy.\u201d<\/p>\n \u201cIt would be a very, very important discovery if made,\u201d he added, \u201cbut it is a needle-in-a-haystack exercise.\u201d<\/p>\n<\/div>\n<\/div>\n