Possibility of detecting magnetospheric radio bursts from Uranus and Neptune

Abstract

EARTH, Jupiter and Saturn are sources of intense but sporadic bursts of electromagnetic radiation which we call magnetospheric radio bursts (MRBs). The Earth's MRBs are observed at kilometric wavelengths, with a power flux spectral peak near 200–300 kHz, a bandwidth roughly half the peak frequency, and a high frequency cutoff near but below the electron gyrofrequency corresponding to the polar surface magnetic field. The Earth's MRBs last a few minutes. Jupiter's MRBs occur at decametric wavelengths, with a power flux spectral peak near 7–8 MHz, a bandwidth again roughly half the peak frequency, and a high frequency cutoff below the polar surface electron gyrofrequency; Jupiter's MRBs also last a few minutes. Saturn's MRBs are observed at hectometric wavelengths, with a power flux spectral peak near 1 MHz and a bandwidth of roughly half the peak frequency, and again last a few minutes. The similarities in the power flux spectra together with the burst occurrence patterns suggest a common physical origin for the MRBs of all three planets. Perhaps the common mechanism is noise amplification by field aligned currents since Gurnett¹ has shown that Earth's MRBs are associated with bright auroral arcs which involve intense field aligned currents. Field aligned currents result from the interaction of the solar wind with the magnetosphere and should be a general feature of the interaction between the solar wind and a planetary magnetosphere (Vasyliunas² and Kennel³). If MRBs are ultimately produced by the solar wind–magnetosphere interaction, their total radiated power might scale as the solar wind power input into the magnetosphere. Kaiser and Stone⁴ have suggested the frequency of emission scales as the polar magnetic field strength of the planet. Here, we scale the intensity of MRBs to the solar wind input and the frequency of emission to the polar field strength to estimate the possibility of detecting MRBs from Uranus and Neptune.