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There are various ways scientists hope to detect intelligent life in space. From monitoring incoming radio signals, looking for visual signatures of a habitable world, to wearing tinfoil hats with antenna arrays, perhaps the most interesting way is to look for their mega-engineering projects. Mega-engineering is concerned with structures and projects on a tremendous scale. It's not unreasonable to think that our astronomical neighbors haven't already tried this; the demand for more resources and places to house a growing population makes astroengineering a common-sense goal. For example, Dyson Spheres are hypothetical structures they might make that we could detect. The former could take care of energy, but what about raw resources: minerals and precious metals? Look no further than your friendly neighborhood asteroid belt.
Asteroid mining makes sense. Even on Earth today, asteroid mining companies, backed by innovators and visionary billionaires, are developing plans and technologies to aid them in the upcoming space ''gold rush'' of the 21st century. Silicon, platinum, palladium, nickel, and water, which can be broken down into hydrogen and oxygen to make rocket fuel, are all examples of lucrative gems to be found, according to a Wired article. It's not hard to imagine why an advanced civilization would take advantage of these opportunities, as well as extensively develop the corresponding infrastructure required for such a large scale operation. The interesting thing about this is that mining in space produces evidence that we can detect.
Since our miners would be digging only for certain species of chemicals, the chemical content of the asteroid belt would not resemble what we'd expect if left untouched. Since asteroid belts and their parent star are formed from the same primordial interstellar dust, (described in a process called the nebular hypothesis), scientists can predict the chemical makeup of far-away asteroid belts by looking at the metal content of the parent star. With spectroscopy, which analyzes the light emitted off of astronomical objects (such as asteroid belts) and from their stars, we can ascertain all this information. Different chemical species will produce different spectral lines, so if we use spectroscopy and notice a debris field missing several chemical species that ought to be there, that is difficult to explain.
Another way scientists can browse for space mining projects is by considering the size many asteroids in the belt should be, and comparing that with what sizes they actually are. The large asteroids would likely be the victims of mining endeavors, increasing the relative number of smaller bodies compared to larger ones, and thus changing the size distribution of the belt. We can predict the approximate size distribution by accounting for the radiation pressure and balance of gravity. (If that's not a powerful example of the predictive power of scientific theory and mathematics, then I don't know what is). Of course, evidence of this occurrence alone isn't good proof of industrious miners; the same result could occur through the impacts of large bodies, but it does raise an eyebrow. Your hopes of finding extraterrestrial intelligence here would be encouraged if there were further evidence of thermal fluctuations in the belt. Industrial mining would create an unusual temperature distribution, as the mechanical process would heat up dust significantly and toss it out.
It's not the most reliable way to conduct SETI inquiries, but asteroid mining enterprises present a hypothetical way to detect, and narrow down astrobiological candidates. It is a little disappointing that a mining operation would have to be very large-scale to detect, and that our instruments of detection need further refinement for our goal. On the other hand, the more ideas we have that could be used to look for life in the universe, the better!
For further reading:
1. Forgan. D. et al. Extrasolar Asteroid Mining as Forensic Evidence for Extraterrestrial Intelligence. International Journal of Astrobiology. 10, 307-313 (2011)
2. Wall. M. ''New Asteroid Mining Company Aims to Manufacture Products in Space''. Wired. (2013).
3. Villard. R. "Asteroid Forensics May Point to Alien Space Miners". Discovery. (2011).
4. Morley. C. "Could We Observe Aliens Mining Asteroids?''. Astrobites. (2011).
Image credit: (Via NASA/JPL-Caltech)
