A Statistical Model for Determining the Probability of Observing Exoplanetary Radio Emissions

Abstract:

The idea that extrasolar planets should emit radiation in the low-frequency radio regime is a generalization of the observation of decametric and kilometric radio emissions from magnetic planets in our own solar system, yet none of these emissions have been observed. Such radio emissions are a result of the interactions between the host star’s magnetized wind and the planet’s magnetosphere that accelerate electrons along the field lines, which leads to radio emissions at the electron gyrofrequency. To understand why these emissions had not yet been observed, and to guide in target selection for future detection efforts, we took a statistical approach to determine what the ideal location in parameter space was for these hypothesized exoplanetary radio emissions to be detected.

We derived probability distribution functions from current datasets for the observably constrained parameters (such as the radius of the host star), and conducted a review of the literature to construct reasonable probability distribution functions to obtain the unconstrained parameters (such as the magnetic field strength of the exoplanet). We then used Monte Carlo sampling to develop a synthetic population of exoplanetary systems and calculated whether the radio emissions from the systems were detectable depending on the angle of beaming, frequency (above the ionospheric cutoff rate of 10 MHz) and flux density (above 5 mJy) of the emission. From millions of simulations we derived a probability distribution function in parameter space as a function of host star type, orbital radius and planetary or host star radius. The probability distribution function illustrated the optimal parameter values of an exoplanetary system that may make the system’s radio emissions detectable to current and currently under development instruments such as the SKA.

We found that detection of exoplanetary radio emissions favor planets larger than 5 Earth radii and within 1 AU of their M dwarf host.