 The first evidence for the existence of Jupiter's magnetic field came in 1955, with the discovery of the decametric radio emission or DAM.As the DAM's spectrum extended up to 40 MHz, astronomers concluded that Jupiter must possess a magnetic field with a maximum strength of above 1 milliteslas (10 gauss).In 1959, observations in the microwave part of the electromagnetic (EM) spectrum (0.1–10 GHz) led to the discovery of the Jovian decimetric radiation (DIM) and the realization that it was synchrotron radiation emitted by relativistic electrons trapped in the planet's radiation belts.