Detection of a radio emission at 3 kHz in the outer heliosphere

A radio source in the outer heliosphere has been detected by the plasma wave receivers on Voyagers 1 and 2. The radio emission is observed in the frequency range 2–3 kHz, and is above the local solar wind electron plasma frequency whenever supporting plasma density data are available. The maximum spectral density of the emission recorded is ∼10−14 V2 m−2 Hz−1. The bandwidth of the radio noise is ∼1 kHz. Possible sources include continuum radiation from Jupiter's distant magnetotail and radiation at the second harmonic of the plasma frequency at the heliopause. If the latter interpretation is correct, these data represent the first remote observations of the heliopause.