If the Ingenuity helicopter would fly at night on Mars, its very possible the whirring rotors would create enough static electricity in the extremely dry Martian atmosphere to cause the air around the craft to glow.

“The faint glow would be most visible during evening hours when the background sky is darker,” said William Farrell, from Goddard Space Flight Center and lead author of a paper on this topic. “NASA’s experimental Ingenuity helicopter does not fly during this time, but future drones could be cleared for evening flight and look for this glow.”

NASA’s Ingenuity Mars Helicopter can be seen hovering during its third flight on April 25, 2021, as seen by the left Navigation Camera aboard NASA’s Perseverance Mars rover. Credit: NASA/JPL-Caltech

If you’ve ever shuffled your feet across a wool carpet on a dry winter day, and then reached out to touch a metal doorknob, you’re familiar with the static discharge that creates a little zap — a spark — that leaps between your fingers and the metal knob.

On Earth, this static discharge is usually just an annoyance. But on Mars, anything “rubbing” against the uber-dry atmosphere – and even the dry soil — can create a phenomenon called triboelectric charging.

When certain pairs of materials, such as a carpet and your shoes rub together, one material gives up some of its electrons to the other material. The separation of charge can create an electric field. This process also occurs naturally at much larger scales on Earth as a corona or electrical glow sometimes seen on aircraft and ships in electrical storms known as Saint Elmo’s Fire.

Although the currents generated by a drone or tiny helicopter like Ingenuity are really small, Farrell said they might be large enough to cause the air around the blades and other parts of the craft to glow a blue-purple color.

“The electric currents generated by the fast-rotating blades on drones are too small to be a threat to the craft or the Martian environment,” he said in a press release, “but they offer an opportunity to do some additional science to improve our understanding of an accumulation of …. triboelectric charging.”

The paper, “Will the Mars Helicopter Induce Local Martian Atmospheric Breakdown?” was published in March 2021 in the Planetary Science Journal.

An animated gif of the Perseverance rover looking at the Ingenuity helicopter. Credit: NASA/JPL

There has been concern about triboelectric charging because on Mars and the Moon, conditions are ideal for this to occur, especially in the soil. The soil is drier than desert sand on Earth, and when materials used on rover wheels – such as aluminum or steel – rub against the soil, it could create enough electric charge to create problems for the craft’s electronics. Therefore, grounding systems have been developed to counteract the issue.

But Ferrell and his team looked at the possibility of this happening for drones or rotocraft on Mars, as well, due to the dryness of the air, as well as the propensity of dust within the Martian air.

The team applied laboratory measurements and used computer modeling to investigate how electric charge could build up on a drone’s rotor blades. They found that as the drone’s blades spin, they can run into the tiny dust grains in the Martian air, especially when the helicopter is near the surface and blowing dust around.

As the blades impact the grains, charge is transferred, building up on the blades and creating an electric field. As charge builds to high levels, the atmosphere starts to conduct electricity, a process known as “atmospheric breakdown,” creating a population of electrons that form an enhanced electric current that acts to dissipate or
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