One of the strongest signs of life outside Earth was announced this week, but some astronomers cautioned that it is extremely difficult to verify. That raises the question: will there ever come a point where we have definitive evidence of extraterrestrial life, and when might that be?

The supposed signs of life were picked up by the James Webb Space Telescope (JWST) from the exoplanet K2-18b, 124 light years away. Nikku Madhusudhan at the University of Cambridge and his colleagues reported a signal of dimethyl sulphide (DMS), a molecule that…