If we want to find intelligent aliens, we should be looking for signs of mining in extraterrestrial asteroid belts, argue two astrophysicists.
Duncan Forgan at the University of Edinburgh and Martin Elvis at the Harvard Smithsonian Center for Astrophysics argue that any advanced civilisation is likely to engage in mining on a large scale, and that this should in theory be visible to current and future telescopes.
First, they say, simply moving materials around the solar system would distort the expected chemical signature in the debris ring around a star.
Second, the activity would alter the distribution of objects in the asteroid belt: mining large objects would make more sense than small ones, so there would be fewer big asteroids in a system that had been systematically mined.
Third, mining would create lots of dust, which would be easily visible thanks to its effects on local temperatures.
Using the star Vega as an example, the team looked to see whether any of these phenomena could be confused with natural processes.
"We find that individual observational signatures of asteroid mining can be explained by natural phenomena, and as such they cannot provide conclusive detections of ETIs [extra-terrestrial intelligences]," they say.
But, say the authors, "They could provide a means of identifying unusual candidate systems for further study using other SETI techniques."