The above display is a frequency-time spectrogram. The results in this figure show an increasing plasma density as Juno descended into Jupiter’s ionosphere during its close pass by Jupiter on 02 February 2017.
The intensity, or amplitude, of the waves is displayed based on the color scale shown on the right. The actual observed frequencies of these emissions approach 150 kHz. To get the sounds into a range we can hear, the 150 kHz signal was reduced 60 times. The momentary, nearly pure tones follow a scale related to the electron density, and are likely associated with an interaction between the Juno spacecraft and the charged particles in Jupiter’s ionosphere. The exact source of these discrete tones is currently being investigated.