Discovery
It has been suggested that the radio emissions from Jupiter's magnetosphere may have been first heard by Nikola Tesla in 1899, when he claimed to have possibly received radio signals from Martians. As early radio receivers were very broadband (as waveband filters were not common until the 1920s), it would have been possible for the Jovian shortwave emissions to have been received by Tesla. Tesla confusing the emissions as coming from Mars may have been due to Mars and Jupiter being located close to each other in the sky at the time. 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 strength of about 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. These synchrotron emissions were used to estimate the number and energy of the electrons around Jupiter and led to improved estimates of the magnetic moment and its tilt.
By 1973 the magnetic moment was known within a factor of two, whereas the tilt was correctly estimated at about 10°. The modulation of Jupiter's DAM by Io (the so-called Io-DAM) was discovered in 1964, and allowed Jupiter's rotation period to be precisely determined. The definitive discovery of the Jovian magnetic field occurred in December 1973, when the Pioneer 10 spacecraft flew near the planet.
Read more about this topic: Magnetosphere Of Jupiter
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