The search for extraterrestrial life usually looks towards places where water, organic molecules or, in the case of technological civilizations, radio signals and laser emissions may exist. But there is another possibility: that a civilization has long disappeared and that all that remains of it are tiny remnants of its technology.. Not an abandoned ship or a monumental structure, but microscopic particles traveling through space. A team of scientists proposes to look for them in an unexpected place: the Moon.
The study, led by Lewis J. Pinault of the SETI Institute, proposes using the lunar regolith (the layer of dust and fragments that covers the surface of our satellite) as a kind of archaeological archive of the galaxy. The idea is based on an exceptional characteristic of the Moon: it lacks an atmosphere, liquid water and geological activity comparable to that on Earth, so the materials that reach its surface can remain there for extraordinarily long periods.
Pinault’s team has studied what would happen if a technological civilization produced tiny, resilient particles, either as waste from its space activities or as a consequence of large-scale engineering projects. Some could escape their planetary system and enter interstellar space. If they survived the journey, a small fraction could end up reaching other star systems, including our own.
The calculations indicate that Refractory particles of about 0.3 micrometers in radius, about three thousandths of a millimeter, could travel distances of kiloparsecs over hundreds of millions of years. The trip would not be easy: the particles would undergo interaction with interstellar gas and erosion processes, while solar radiation and the heliosphere would act as filters. However, the models show that there would be an arrival channel slow enough for a small fraction to survive the impact with the Earth-Moon system.
This is where the advantage of our satellite appears. For about 4 billion years, the lunar surface has been accumulating dust from space. On Earth, rain, wind, oceans, and geological activity continually redistribute and destroy ancient materials. On the Moon, however, a particle can be buried and preserved for enormous periods. It is, in a way, a library of the history of the solar system and its galactic environment.
The proposal consists of analyzing approximately one cubic meter of regolith. It would not be necessary to examine each grain one by one: the authors propose combining microscopy, tomography, spectroscopy and artificial intelligence systems capable of classifying large quantities of particles to detect those with anomalous properties. The candidates could then undergo detailed analyzes of their composition and structure. The challenge would be distinguish a possible artificial particle from the enormous amount of natural material present in the lunar soil. It wouldn’t be enough to find something strange. It would be necessary to demonstrate that its chemical, physical or structural characteristics are difficult to explain by natural processes.
And here appears one of the most interesting aspects of the study: even finding nothing would be a scientific result. ANDPinault’s team calculates that a negative analysis of one cubic meter would allow limits to be established on the amount of technological material that certain civilizations could have produced and dispersed throughout the galaxy. In one of their scenarios, the absence of particles would rule out that Sun-like stars have typically dispersed more than about 0.10 Earth masses of long-lasting artificial debris throughout galactic history.
There is also a much more favorable scenario for the search: that a civilization does not limit itself to releasing waste into space, but deliberately sends particles towards other systems. Then, the probability of finding them could be several orders of magnitude higher, depending on the frequency of those visits and the amount of material deposited.
The proposal comes at a particularly opportune time. Future lunar missions, including Artemis and Chang’e, will return carefully documented new samples and will increase the amount of material available for this type of analysis. Instruments capable of studying regolith directly on the lunar surface could also be developed.
For now, there is no evidence that those particles are there. The work is in the process of peer review. What it offers is something more modest and, perhaps for that reason, more interesting: a way of transforming speculation into an experiment. Instead of asking if any extraterrestrial civilization could exist, The authors propose to look for one of the things that any technological civilization could leave behind: its waste. If an unexplainable particle ever appears, we may not have to listen to a signal from the stars. It would be enough to look at a grain of lunar dust.