# A challenge for Martian lightning: Limits of collisional charging at low pressure

## TL;DR

This study investigates how ambient pressure affects collisional charging of basalt grains, revealing that Martian pressures significantly limit charge buildup and thus reduce lightning potential compared to Earth.

## Contribution

It provides the first detailed analysis of collisional charging at Martian pressures, showing the limitations of lightning generation on Mars due to low ambient pressure.

## Key findings

- Charge on grains is minimized at Martian pressure (~6 mbar).
- Charge increases steeply at pressures below a few mbar.
- Martian conditions significantly reduce the likelihood of lightning.

## Abstract

Collisional charging is one potential initial step in generating lightning. In this work, we study the charging of colliding monodisperse, spherical basalt grains depending on ambient pressure. We used grains of 1.0 to 1.2 mm in one set and 2.0 to 2.4 mm in another set. We varied the ambient pressure between 0.03 mbar and 80 mbar. This especially includes Martian pressure being 6 mbar on average. At a few mbar the net charge gathering on colliding grains has a minimum. A smooth incline in charging occurs for larger pressures. Toward lower pressure the charge increases steeply. The pressure dependence is in agreement to a model where the maximum charge is limited by a gas discharge occurring between two charged colliding grains shortly after or before a collision. The capability of building up charge is at a minimum exactly in the range of Martian pressures. The charges on grains are at least a factor 5 smaller than at the highest pressure tested and still smaller compared to ambient pressure on Earth. This implies that on Mars collisional charging and the potential of subsequent generation of lightning or other large scale discharges are strongly reduced compared to Earth. This might result in less frequent and less energetic lightning on Mars.