“The search for extraterrestrial intelligence (SETI) could be taking the wrong approach. Instead of listening for alien radio broadcasts, a better strategy may be to look for giant structures placed in orbit around nearby stars by alien civilisations.

‘Artificial structures may be the best way for an advanced extraterrestrial civilisation to signal its presence to an emerging technology like ours,’ says Luc Arnold of the Observatory of Haute-Provence in France. And he believes that the generation of space-based telescopes now being designed will be able to spot them.” (New Scientist)

Arnold does not make a compelling case, to my way of thinking, about why a civilization would go to the trouble (oops! it might be no trouble for them…) of doing this rather than merely broadcasting their presence. His argument seems to arise from nothing so much as that our telescopes have recently gotten powerful enough to spot a planet-sized object transiting a star.