Electrostatic instability of non-spherical dust in sub-stellar clouds

TL;DR

This paper investigates the electrostatic stability of charged non-spherical dust grains in sub-stellar clouds, deriving stability criteria and analyzing implications for atmospheric chemistry, polarization, and grain morphology.

Contribution

It provides the first analytical stability criterion for charged spheroidal dust grains considering size, potential, and tensile strength, and explores their electrostatic discharges and polarization effects.

Findings

Stable dust grains have eccentricities below a critical value.

Electrostatic instability leads to electric field enhancement at spheroidal poles.

Unstable grains may undergo electrostatic erosion, affecting their shape and porosity.

Abstract

Charged dust clouds play an important role in the evolution of sub-stellar atmospheres through electrical discharges such as lightning events or inter-grain discharges. The consequent plasma activation presents an alternative source of disequilibrium chemistry, potentially triggering a set of chemical reactions otherwise energetically unavailable. The aim of this paper is to address the problem of the electrostatic stability of charged spheroidal dust grains in sub-stellar clouds and its impact on inter-grain electrostatic discharges, the available area for atmospheric gas-phase surface chemistry, the particle eccentricity distribution function and observed polarization signatures. This paper has derived the criterion for the allowed values of dust eccentricity that are electrostatically stable as a function of grain size $a\in[0.2,1.8]~\mu$m, floating potential $\phi_{f}\in[1, 10]$~V and tensile strength $\Sigma_{s}=10^{3}$~Pa. As a consequence of electrostatic instability we also calculate the expected electric field enhancement at the spheroidal poles, the increased surface area of a dust grain, the truncation of the particle eccentricity distribution function and the resultant degree of polarization. Dust grains with an eccentricity below a critical value will be electrostatically stable; whereas, grains with an eccentricity above a critical value will be unstable. The results presented here are applicable not only to spheroidal dust grains but any non-spherical dust grains where non-uniform surface electric fields or inhomogeneous tensile strengths could be susceptible to electrostatic instability. In this context electrostatic erosion presents a mechanism that may produce bumpy, irregularly shaped or porous grains.