Why Study Jovian Radio Waves?
Jupiter was one of the first radio sources discovered with early radio telescopes on Earth. It is
one of the "brightest" radio sources in the sky.
Early studies of Jovian radio emissions told us that Jupiter had a strong internal magnetic field
and that Io was a very important member of the Jovian system, since its position about Jupiter
strongly affects the strength of Jovian radio emissions.
Galileo studies of Jovian radio waves greatly extend Earth-based and previous spacecraft studies
of Jovian radio emissions.
Radio emissions provide a method of remotely sensing plasmas not studied directly by Galileo.
The following displays are called frequency-time spectrograms because they show the intensities of waves as a function of frequency (vertical axis) and time (horizontal axis). Colors are used to convey intensity with red being used for the most intense waves and blue for the least intense waves.
In this spectrogram a number of different types of Jovian radio waves are shown. Since many of the names are long, radio astronomers have assigned acronyms to some of them. DAM stands for decametric radiation. Galileo only observes the lower frequency portion of this type of emission; it normally goes to about 40 MHz and this upper frequency limit provided early radio astronomers with a surprisingly accurate estimate of the strength of the internal Jovian magnetic field. HOM stands for hectometric radiation. This emission is thought, like DAM, to be generated near Jupiter associated with auroras. The source of broadband kilometric radiation bKOM is not yet well identified. It likely comes from the high Jovian auroral zone, but could also be generated near the Io torus. Escaping and trapped continuum radiation are low-frequency radio emissions generated quite some distance from the planet but in the magnetosphere. The trapped emissions cannot leave the magnetosphere because their frequency is lower than the surrounding solar wind plasma will allow to propagate, hence, they are trapped in the Jovian magnetosphere.
In addition to the examples shown in the upper spectrogram, this panel shows narrowband kilometric radiation nKOM. These emissions are known to be generated near the outer edge of the Io plasma torus at a distance of 8 or 9 Jovian radii from Jupiter. In fact, it is thought that high frequency ECH (electron cyclotron harmonic) bands (also shown in this spectrogram) may be the source for the nKOM radio emissions.