[troutman]

How could we detect aliens? Ancient artifacts?

https://astrobiology.nasa.gov/news/artifacts-in-space/

Longtime SETI scientist and advocate Jill Tarter, for instance, wondered if the signatures of intelligent civilizations could be imprinted on neutrinos. She said that a leak of the radioactive isotope tritium, which has a short 12-year half-life, could also signal the presence of advanced life because (unless it’s near a supernova) it would have to come quite recently from a nuclear reactor.

Taking it further, she and others argued that artifacts of intelligent life would include many atmospheric and planetary changes that could only be accomplished by intelligent beings. For instance, the presence of unnatural pollutants such as chloroflurocarbons (CFCs) or sulfur hexafluoride (SF6) in an exoplanet atmosphere would, in this view, be an “artifact” of civilization.

https://www.forbes.com/sites/brucedo...h=3647ee0a195a

“[Evidence of past] mining or quarrying could show up in gravimetry or magnetic surveys, even if an ancient mine was buried under the lunar regolith,” said Davies. “We could detect [alien] nuclear waste perhaps from a lunar satellite by looking for localized gamma ray sources from the lunar surface.”

“In searching for artifacts, one is looking for ‘something fishy’," said Davies. “But ‘fishiness’ requires a human decision in advance about a signature of artificiality. There are some simple examples, like right angle edges. But we have little idea what million year-old technology might look like.”