A theory explaining Jupiter's banded whistler emission in particular low-frequency hiss and chorus is proposed. It is shown that superthermal electrons described by a kappa distribution function cause whistler instability below one-third of the electron gyrofrequency, whereas a two temperature Maxwellian leads to a band of unstable growing modes just below one-half of the electron gyrofrequency. A superposition of both yields almost exactly the structure of whistler mode hiss and chorus detected by the Voyager 1 and 2 plasma wave instrument.