Planets that look alike might be a sign of spacefaring aliens

Nearby planets that look unusually alike could be a sign of spacefaring alien life that has travelled between stars, researchers have suggested.

Astronomers searching for extraterrestrial life tend to look for specific signals, either in the form of “biosignatures” – molecules that are only produced by biological processes – or “technosignatures”, abnormal patterns of light that may have been produced by technologies.

Both of these rely on assumptions…