Searching for Exoplanets with Low-Frequency Radio
Non-thermal, low-frequency radio emissions from the Earth, Jupiter, Saturn, Neptune, and Uranus have been observed for decades. They are now "understood" to be caused by the cyclotron-maser instability (CMI) from unstable keV electron distributions in the planetary magnetospheres. It stands to reason that this process is also at work in the purported magnetospheres of extrasolar planets. Particularly from ”Hot Jupiters”, extrasolar Jupiter-size planets that orbit their primary at very close range, we expect the radiated power to be strong enough to allow detection from Earth. Also, exoplanets orbiting stars that are relatively near our solar system should be good targets. However, to date no definitive detections have been made in the radio regime.
But exoplanet emissions will eventually be detected, and their characterization will lead directly to the determination of various parameters, such as the planetary magnetic field, the planet's rotation period, and aspects of interior composition. These parameters are difficult to obtain using any of the optical or astrometric techniques. The spectrum of the emission will establish the magnetic field strength of the planet and place constraints on its magnetosphere and possible interaction with a stellar wind. If satellites orbit the planet, their presence could be inferred through modulation of the CMI emission, as is the case for the Io-modulated emission from Jupiter. And importantly, the radio method benefits from stellar activity, thus opening up a window to star systems not observable with other methods.