Lightning May Create Martian Perchlorates and Carbonates

The thin atmosphere of Mars, visible on the horizon in this image taken by the Viking 1 spacecraft. Credit: NASA.

Electrostatic discharges, such as lightning, occur after sufficiently large charge differences arise within planetary atmospheres. These charge differences result from collisions between aerosol particles (the triboelectric effect). Lightning provides a source of energy to both break down and form new gaseous and solid substances. The molecules formed by lightning could be useful as part of in-situ resource utilization (ISRU) campaigns and could be sufficiently abundant to be of geological significance, as in the case of martian perchlorates (compounds containing a chlorine atom bonded to four oxygen atoms).

To determine whether perchlorates could be produced on Mars by lightning in large quantities, Alian Wang from Washington University in St. Louis and colleagues performed laboratory experiments simulating the effect of electrostatic discharge on chlorides in Mars-like conditions. Using Raman and MIR spectroscopy, the researchers observed that after seven hours of electrostatic discharge on potassium and magnesium chloride, 0.07% of the chlorine present was in the form of chlorates and perchlorates, while 1.1% had been released into the atmosphere. Additionally, 0.33% of the potassium and magnesium was found to be in the form of carbonates after discharges. Wang and colleagues hypothesize that potassium and magnesium oxide were also formed, though they were not detected because these spectrometers are relatively insensitive to the oxides. Based on their experiments, Wang and colleagues roughly estimate that lightning in global dust storms could have formed the observed quantities of perchlorates and carbonates on the surface of Mars over the course of about a third of the age of Mars, suggesting that lightning could be solely responsible for perchlorates and carbonates at Mars. The electrical properties of dust at Mars, as well as lightning on Mars, are not well observed, and this work highlights the importance of improved observation of electrical phenomena at Mars. READ MORE