Planetary radio astronomy: Earth, giant planets, and beyond

[摘要] The magnetospheric phenomenon of non-thermal radio emission is known sincethe serendipitous discovery of Jupiter as radio planet in 1955, opening thenew field of "Planetary Radio Astronomy". Continuousground-based observations and, in particular, space-borne measurements havemeanwhile produced a comprehensive picture of a fascinating research area.Space missions as the Voyagers to the Giant Planets, specifically Voyager 2further to Uranus and Neptune, Galileo orbiting Jupiter, and now Cassini inorbit around Saturn since July 2004, provide a huge amount of radio data,well embedded in other experiments monitoring space plasmas and magneticfields. The present paper as a condensation of a presentation at theKleinheubacher Tagung 2013 in honour of the 100th anniversary of Prof. KarlRawer, provides an introduction into the generation mechanism of non-thermalplanetary radio waves and highlights some new features of planetary radioemission detected in the recent past.

As one of the most sophisticated spacecraft, Cassini, now inspace for more than 16 years and still in excellent health, enabled for thefirst time a seasonal overview of the magnetospheric variations and theirimplications for the generation of radio emission. Presentlymost puzzling is the seasonally variable rotational modulation of Saturnkilometric radio emission (SKR) as seen by Cassini, compared with earlyVoyager observations.

The cyclotron maser instability is the fundamental mechanismunder which generation and sufficient amplification of non-thermal radioemission is most likely. Considering these physical processes, furthertheoretical investigations have been started to investigate the conditionsand possibilities of non-thermal radio emission from exoplanets, frompotential radio planets in extrasolar systems.

[学科分类] 电子、光学、磁材料