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

TL;DR

This paper investigates the potential for lightning-induced radio emissions on exoplanet HAT-P-11b, analyzing the conditions needed for such signals to be detectable and suggesting future observational prospects.

Contribution

It extends previous models of exoplanet lightning radio emissions by conducting a parameter study and estimating the extreme lightning activity required for detection.

Findings

Detection would require lightning activity comparable to Earth's volcanic eruptions.

Estimated lightning flash densities need to be millions of times higher than Earth's most active storms.

Future observations could potentially detect lightning on exoplanets through radio and infrared signals.

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 Hodos\'an et al. [2016a]. After a summary of our previous work [Hodos\'an et al. 2016a], we extend it with a parameter study. The lightning activity of the hypothetical storm is largely dependent on the radio spectral roll-off, $n$, and the flash duration, $\tau_\mathrm{fl}$. 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, $3.8 \times 10^6$ times larger flash densities than the Earth-storms with the largest lightning activity is needed to produce the observed signal from HAT-P-11b. Combined with the results of Hodos\'an 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.