The Radiometric Bode's Law and Extrasolar Planets

We predict the radio flux densities of the extrasolar planets in the current census, making use of an empirical relation—the radiometric Bode's law—determined from the five "magnetic" planets in the solar system (the Earth and the four gas giants). Radio emission from these planets results from solar wind-powered electron currents depositing energy in the magnetic polar regions. We find that most of the known extrasolar planets should emit in the frequency range 10-1000 MHz and, under favorable circumstances, have typical flux densities as large as 1 mJy. We also describe an initial, systematic effort to search for radio emission in low radio frequency images acquired with the Very Large Array (VLA). The limits set by the VLA images (≈300 mJy) are consistent with, but do not provide strong constraints on, the predictions of the model. Future radio telescopes, such as the Low Frequency Array and the Square Kilometer Array, should be able to detect the known extrasolar planets or place austere limits on their radio emission. Planets with masses much lower than those in the current census will probably radiate below 10 MHz and will require a space-based array.