Mesospheric optical signatures of possible lightning on Venus

TL;DR

This paper models mesospheric optical emissions on Venus caused by intra-cloud lightning, predicting detectable transient glows in the ultraviolet to infrared range that depend on lightning properties and observation distance.

Contribution

It introduces a self-consistent 2D model linking Venusian lightning activity to mesospheric optical signatures, predicting observable transient glows.

Findings

Electric fields exceed breakdown values in Venus's mesosphere.

Transient glows in UV, visible, and IR are predicted above lightning sources.

Detection is feasible within 300-1000 km distance using current instruments.

Abstract

A self-consistent two-dimensional model is proposed to account for the transient mesospheric nighttime optical emissions associated to possible intra-cloud (IC) lightning occurring in the Venusian troposphere. The model calculates the mesospheric (between 75 km and 120 km in altitude) quasielestrostatic electric field and electron density produced in response to IC lightning activity located beween 40 km and 65 km in the Venusian cloud layer. The optical signatures and the densities of perturbed excited atomic and molecular neutral and ionic species in the mesosphere of Venus are also calcutated using a basic kinetic scheme. The calculations were performed for different IC lightning discharge properties [Krasnopolsky (1980), Cosmic. Res.]. We found that the calculated electric fields in the mesosphere of Venus are above breakdown values and that, consequently, visible transient glows (similar to terrestrial Halos produced by lightning) right above the parent IC lightning are predicted. The transient optical emissions result from radiative de-excitation of excited electronic states of N$_2$ (in the ultraviolet, visible and near infrared ranges) and of O($^{1}$S) and of O($^{1}$D) in, respectively, the green (557 nm) and red (630 nm) wavelengths. The predicted transient lightning induced glows from O($^{1}$S) can reach an intensity higher than 167 R and, consequently, be above the detection threshold of the Lightning and Airglow Camera (LAC) instrument aboard the japanese Akatsuki probe orbiting Venus since Dec 2015. However, according to our model, successful observations of transient lightning-induced optical glows could only be possible for sufficiently close (300 km or maximum 1000 km) distances.