Electric purple glow can ignite Martian dust storms

 

(Image credit: NASA)

An eerie effect close to St. Elmo's fire on Earth could be created by colliding dust particles.

NASA's Perseverance rover could soon have a front-row view of an otherworldly light show from its new home on the Red Planet.

The air around the rover could crackle and glow with purple light from the collision of statically charged dust particles when the next seasonal dust storm passes through Jezero crater (where the rover landed on Feb. 18), a new study suggests.

According to lead study author Joshua Méndez Harper, a geologist at the University of Oregon, these colorful sparks will almost certainly be too tiny and frail to pose a threat to Perseverance, or to any hypothetical human being who would alight on Mars in the future. The presence of electrostatic forces on Mars, however, may have wide-ranging consequences for how scientists understand the atmosphere of the Red Planet and its life-fostering potential, Méndez Harper said.

Méndez Harper said that tiny sparks can catalyze the creation of chemicals that can [influence] the existence of organic materials. A recent paper indicated that small-scale discharges can generate perchlorates, compounds toxic to many types of life.

The buzz about Mars

The new research, which is set to be published in the March issue of the journal Icarus, aims to respond decisively to a question which, for half a century, has buzzed around the scientific community: Will colliding particles whipped up in Mars' atmosphere by high-speed winds spark electricity?

This process is known as triboelectric charging, i.e. electricity produced by the friction of particles or surfaces that collide. On Earth, by rubbing your socks on the carpet and then touching a metal doorknob (youch!), you can create a tiny triboelectric spark, or static electricity, in your bedroom. Or you can marvel at an apocalyptic lightning storm bolting through an erupting volcanoes ash column, the triboelectric result of ash particles colliding in the air, for a bigger demonstration.

(Image credit: NASA)


It's unknown on Mars, however, if triboelectric charging occurs at all. Since Mars has far lower atmospheric pressure than Earth does, powerful charges are unlikely to build up there, said Méndez Harper. By shaking up volcanic ash in small, low-pressure tanks, experiments dating back to the 1970s have attempted to recreate Martian dust storms on Earth. These particles (which have similar compositions to Martian dust) often spark — but these studies may be fundamentally flawed, according to the new Icarus paper.

The probability of charging resulting from the interaction between simulated Martian dust and experimental containers enclosing it was not accounted for by these works, Méndez Harper said. The containers also had wildly different substances that may have caused the electrical effects observed, such as plastic, metal or glass.

In other words, any sparks detected in past experiments may actually have been between a particle of dust and the side of the container enclosing it, rather than between two simulated particles of Martian dust. These containers are made up of objects that do not exist on Mars, meaning that the tests do not really tell us much about what is happening in the dust storms of the Red Planet.

In their new research, Méndez Harper and his colleagues tried to fix this experimental design error.

 

The team used volcanic ash grains (from Mexico's Xitle volcano, which erupted around 1,700 years ago) to simulate Martian dust particles, similar to previous experiments, and enclosed them in a glass tube under conditions that simulated the Martian atmosphere. However, unlike previous experiments, the team used carbon dioxide jets to stir the grains into a' fountain' of colliding particles that never reached the wall of the jar.

The team found that, even though those dust grains did not come into contact with the container, the colliding particles resulted in tiny triboelectric sparks. This analysis, then, provides the researchers with the first reliable experimental proof of triboelectric charging on Mars.

Red planet, purple glow

What were those charges going to look like? It's impossible to say. Although the researchers electronically observed shocks in their Martian dust fountain, they did not notice any visual effects arising from the collisions. It's doubtful that even the fiercest dust storms will ripple with lightning the way terrestrial volcanoes or thunderclouds do, given the low atmospheric pressure on Mars.

A more possible possibility is that Martian dust storms show countless tiny sparks, Méndez Harper said, named streamer discharges and glow discharges. These small-scale electrical effects could cause Martian dust clouds to glow purple; on Earth, when the masts of ships scrape through a powerful electric field, sailors often see a similar glow, known as St. Elmo's fire.

The next time a dust storm sweeps through the Jezero crater, or maybe even earlier, Méndez Harper said, the Perseverance rover might be able to obtain the first visual evidence of the phenomenon on Mars.

Percy is fitted with a small helicopter called Ingenuity, Méndez Harper said when the copter takes off or lands, its whirring blades will stir up enough dust to "produce noticeable discharges" near the rover.

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