[Previous] | [Session 36] | [Next]
B.J. Butler (NRAO)
At long wavelengths (\lambda > 6 m; \nu < 40 MHz), the emission from Jupiter is dominated by extremely strong and variable cyclotron maser emission. This emission arises from solar wind deposited keV electrons in the magnetosphere, which subsequently develop an anisotropy in their energy distribution, becoming unstable. When these electrons encounter the auroral zones of the planet, emission results at the gyrofrequency of the magnetic field at the location of the electron (fg = 2.8 Bgauss MHz). The emission is very sporadic, but can reach magnitudes of 105 Jy. In addition, the emission is modulated by the satellite Io.
It would be extremely valuable to detect this type of emission from Extrasolar Giant Planets (EGPs), because it provides the following: \begin{itemize} \item Direct detection of the EGP;\\[-7truemm] \item Presence and strength of the EGP magnetic field;\\[-7truemm] \item Existence of satellites;\\[-7truemm] \item Rotation period of the EGP. \end{itemize}
Current predictions (using the so-called ``Radiometric Bode's Law'') suggest that it is possible to detect this type of emission from EGPs, but that it is necessary to catch the planet in an outburst. Even in outburst, the predicted emission is weak, of order mJy. Searches with the VLA at 74 and 330 MHz have been unsuccessful so far [2]. Added sensitivity and lower frequencies are what are needed for more conclusive searches for this emission. There are currently two instruments being proposed to be built which would provide additional sensitivity at low frequencies: LOFAR and SKA. Prospects seem good that at least LOFAR may come on-line within the next decade or so.
\noindent [1] Farrell et al., 1999, JGR, 104, 14025; Zarka et al., 2001, Ap&SS, 277, 293. [2] Bastian et al., 2000, ApJ, 545, 1058.
[Previous] | [Session 36] | [Next]
Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.