Insight into atmospheres of extrasolar planets through plasma processes

TL;DR

This paper explores how plasma processes like lightning, discharge events, and external ionisation influence the atmospheres of extrasolar planets, providing spectral signatures that can be used for remote atmospheric analysis.

Contribution

It introduces a comprehensive overview of plasma phenomena in exoplanet atmospheres and proposes observational signatures for studying these processes.

Findings

Lightning leaves spectral fingerprints such as HCN formation.

Plasma processes cause characteristic damping of electromagnetic emissions.

External ionisation can lead to chromosphere formation.

Abstract

Extrasolar planets appear in a chemical diversity unseen in our own solar system. Despite their atmospheres being cold, continuous and transient plasma processes do affect these atmosphere where clouds form with great efficiency. Clouds can be very dynamic due to winds for example in highly irradiated planets like HD 189733b, and lightning may emerge. Lightning, and discharge events in general, leave spectral fingerprints, for example due to the formation of HCN. During the interaction, lightning or other flash--ionisation events also change the electromagnetic field of a coherent, high energy emission which results a characteristic damping of the initial, unperturbed (e.g. cyclotron emission) radiation beam. We summarise this as 'recipe for observers'. External ionisation by X-ray or UV e.g. from within the interstellar medium or from a white dwarf companion will introduce additional ionisation leading to the formation of a chromosphere. Signatures of plasma processes therefore allow for an alternative way to study atmospheres of extrasolar planets and brown dwarfs.