Cyclotron maser radiation from planetary magnetospheres (abstract)

Abstract

For over 20 years it has been known that the Earth is an intense radio emitter in the frequency range from about 100 to 500 kHz. This radiation is generated at altitudes of about one Earth radius over the northern and southern auroral zones, and is closely correlated with the occurrence of discrete auroral arcs. During active periods, the total radiated power is very large, averaging from 107 to 108 W, with peaks possibly as high as 109 W. It is now widely believed that this radiation is generated by a process known as a cyclotron maser instability. This process involves a Doppler-shifted cyclotron resonance interaction between the free-space R-X mode and the auroral electrons. The most recent data, from the Viking satellite, indicate that the free-energy source driving the instability is produced by electrons trapped by the magnetic mirror force and the electric field response for the auroral particle acceleration. In addition to the Earth, it is now known that four other planetary magnetospheres, at Jupiter, Saturn, Uranus, and Neptune, all have similar types of radio emissions. Also, it has been suggested that certain types of microwave emissions from the Sun, and from binary star systems may also be produced by this same mechanism. Thus, in addition to being a relatively new, interesting plasma physics phenomenon, the cyclotron maser mechanism appears to be important for a broad range of astronomical radio sources.