The Detectability of Radio Auroral Emission from Proxima B

Abstract: Magnetically active stars possess stellar winds whose interaction with planetary magnetic fields produces radio auroral emission. We examine the detectability of radio auroral emission from Proxima b, the closest known exosolar planet orbiting our nearest neighboring star, Proxima Centauri. Using the Radiometric Bode's Law, we estimate the radio flux produced by the interaction of Proxima Centauri's stellar wind and Proxima b's magnetosphere for different planetary magnetic field strengths. For plausible planetary masses, Proxima b produces 6-83 mJy of auroral radio flux at frequencies of 0.3-0.8 MHz for planetary magnetic field strengths of 1-3 B$_{\oplus}$. According to recent MHD models that vary the orbital parameters of the system, this emission is expected to be highly variable. This variability is due to large fluctuations in the size of Proxima b's magnetosphere as it crosses the equatorial streamer regions of the dense stellar wind and high dynamic pressure. Using the MHD model of Garraffo et al. 2016 for the variation of the magnetosphere radius during the orbit, we estimate that the observed radio flux can vary nearly by an order of magnitude over the 11.2 day period of Proxima b. The detailed amplitude variation depends on the stellar wind, orbital, and planetary magnetic field parameters. We discuss observing strategies for proposed future space-based observatories to reach frequencies below the ionospheric cut off ($\sim 10$ MHz) as would be required to detect the signal we investigate.