Radio emissions from Jupiter arise from charged particles moving through Jupiter’s magnetic field. Many of these particles come from the moon Io, which is volcanically active and ejects tonnes of matter into space every second. The radio emissions in the 20 MHz band are thought to derive from synchrotron radiation that is emitted in specific directions according to the changes in the direction of motion of the charged particles. As a consequence, there are at least three intense emission occurrences related to the location of the moon Io and the presence of magnetic storms on Jupiter itself, known as Io-A, Io-B and Io-C. When the orbital positions are favourable, these radio emissions are directed towards Earth where they can be detected.

Below is a graph showing the current orbital phase angle of Io and the Central Meridian Longitude (CML) of Jupiter (represented by the small pink circle), with conditions required for strong radio emissions to be detected from Earth, marked by the coloured ellipses.