Floating in the habitable zone of a distant red dwarf star, K2-18b has become one of the most talked-about exoplanets in recent memory—and for good reason. The recent detection of dimethyl sulfide (DMS), a molecule typically produced by life on Earth, has ignited both excitement and caution among scientists. Could this be a sign of alien biology, or just chemistry playing tricks on us? As telescopes become our time machines and spectrometers our sniffers of distant worlds, K2-18b invites us to rethink what we mean by 'life'—and how we'll know it when we see it.