Ionisation in atmospheres of Brown Dwarfs and extrasolar planets I The role of electron avalanche

TL;DR

This paper explores how electron avalanches triggered by charged dust grains can cause stochastic ionisation in Brown Dwarf and exoplanet atmospheres, potentially affecting magnetic coupling and atmospheric chemistry.

Contribution

It introduces the concept that local discharge events via electron avalanches can occur in these atmospheres, explaining observed ionisation phenomena not accounted for by dust-gas charge equilibrium.

Findings

Electron avalanches can occur on short time scales.

Discharges produce free charges affecting magnetic coupling.

Atmospheric ionisation is more stochastic than previously thought.

Abstract

Brown Dwarf and extrasolar planet atmospheres form clouds which strongly influence the local chemistry and physics. These clouds are globally neutral obeying dust-gas charge equilibrium which is, on short time scales, inconsistent with the observation of stochastic ionisation events of the solar system planets. We argue that a significant volume of the clouds in Brown Dwarfs and extrasolar planets is susceptible to local discharge events. These are electron avalanches triggered by charged dust grains. Such intra-cloud discharges occur on time scales shorter than the time needed to neutralise the dust grains by collisional processes. An ensemble of discharges is likely to produce enough free charges to suggest a partial and stochastic coupling of the atmosphere to a large-scale magnetic field.