Exo-lightning radio emission: The case study of HAT-P-11b

Abstract

Lightning induced radio emission has been observed on solar system planets. Lecavelier des Etangs et al. [2013] carried out radio transit observations of the exoplanet HAT-P-11b, and suggested a tentative detection of a radio signal. Here, we explore the possibility of the radio emission having been produced by lightning activity on the exoplanet, following and expanding the work of Hodosán et al. [2016a]. After a summary of our previous work [Hodosán et al. 2016a], we extend it with a parameter study. The lightning activity of a hypothetical storm is largely dependent on the radio spectral roll-off, n, and the flash duration, τ fl. The best-case scenario would require a flash density of the same order of magnitude as can be found during volcanic eruptions on Earth. On average, 3.8 × 10 6 times larger flash densities than Earth-storms with the largest lightning activity are needed to produce the observed signal from HAT-P-11b. Combined with the results of Hodosán et al. [2016a] regarding the chemical effects of planet-wide thunderstorms, we conclude that future radio and infrared observations may lead to lightning detection on planets outside the solar system.