Among the most abundant molecules in the known biosphere, nitrogen has long confounded astronomers with a paradox: the gas that fills most of Earth's sky leaves almost no fingerprint on the light passing through it. Now, by listening for the brief electrical whisper that occurs when two nitrogen molecules collide, researchers have found a way to give this silent majority a voice — a faint infrared shadow near 4.15 micrometres that may one day help humanity recognize, across interstellar distances, the kind of world it already calls home.