Can We Detect Aliens by Their Space Junk?
Despite the best efforts of SETI (Search for Extraterrestrial Intelligence) scientists, aliens have still evaded our detection. That's not entirely surprising. Unless extraterrestrials are purposely transmitting powerful, focused radio signals in our general direction and we're tuned in, there's little to no chance our telescopes would pick up their broadcasts. And so we're left here, alone and listening.
Clearly, SETI could use a few new tricks, and in a recent article published to the arXiv preprint archive, astrophysicist Hector Socas-Navarro of the Canary Islands Institute of Astrophysics in Spain provides one.
Socas-Navarro suggests applying transit photometry, the highly successful method of discovering exoplanets, to search for alien technology. When an exoplanet transits its host star, it blocks some of the star's light. Astronomers can spot this subtle dimming tens of thousands of light years away, and from it, they can determine a few basic characteristics about the planet itself, including its size and composition.
According to Socas-Navarro, astronomers could potentially also determine the presence of technologically-advanced alien life. He reasons that an alien species might place satellites, space habitats, solar panels, and other objects into geostationary orbit around their planet, just like us, and if this orbit grows cluttered enough, the collective junk, which he termed a "Clarke Exobelt" (CEB), might block out some of the star's light. While it would be exceedingly difficult to spot such a meager dimming with our current telescopes, Socas-Navarro says it isn't impossible. He calculated that if any of the much discussed TRAPPIST-1 exoplanets had sufficiently cluttered orbits, equal to what Earth might have in the year 2200, we may be able to detect their CEBs right now. (Below: a picture of space junk blocking a star's light.)
Socas-Navarro admits that a ring of alien-made space junk might be difficult to distinguish from a ring of natural space junk composed of rocks and planetary debris. But, he says, "These two structures have a different intrinsic geometry."
"Both are extremely thin and flat but in different (perpendicular) directions. Rings are extended in the radial direction and thin in inclination. CEBs, on the other hand, are thin in the radial direction and extended in inclination."
Another obvious drawback of Socas-Navarro's hopeful idea is that advanced alien species might decide to keep their orbits relatively clear. Space junk around our planet is already deemed problematic and ideas are floating around to clean it up. Still, we don't lose anything by watching for CEBs.
"As with any other technomarkers, the search for CEBs is a long shot," Socas-Navarro writes. "We have no idea if they exist or how likely they are to occur. However, given that candidate identification is based on the same light curve observations that are currently demanded in the search for habitable exoplanets, it does not require of any additional effort, at least initially, other than being alert for possible detections."
Source: Hector Socas-Navarro. "Possible Photometric Signatures of Moderately Advanced Civilizations: The Clarke Exobelt." arXiv:1802.07723 [astro-ph.EP]