Why bother asking astronomers to detect life in space? According to Alexey V Arkhipov of the Institute of Radio Astronomy in Kharkhov, Ukraine, people with metal detectors might be a better bet.
Writing in the June issue of The Observatory, a British astronomy magazine, he points out that it is very difficult for small objects to remain in stable orbits in a planetary system.
Instead, they tend to be ejected into deep space by gravitational interactions. Near planets whose civilisations had developed spaceflight, such objects would include spacecraft and pieces of them.
If a nearby star had a planet with significant space projects, for example mining asteroids to make big space structures, we could expect a slow drizzle of bits to arrive on the Earth like natural meteorites do.
Using figures for the number of stars near the Sun, the percentage that might have planets and the amount of material that civilisations on them might turn into spaceships, Dr Arkhipov calculates that such remains could turn up on the Earth every 117 years. That would still mean that 4,000 such objects would have appeared on the Earth during its history.
He says that "the possibility of artefact finds in pre-human layers and reports of unusual meteorites are worth objective analysis".
Several meteorites per year arrive at the Earth's surface but none has ever shown signs of being an engineered object.