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Martian dust tends to cling to surfaces such as solar panels due to electrostatic charge.

  • Martian dust is extremely small and fine-grained. Atmospheric dust on Mars is approximately three microns in diameter, and adheres via electrostatic forces. You can't just "brush it off" like you would on Earth; much dust would remain.

Is this charge mostly negative? Mostly positive? Roughly equal amounts of each? Dependent on the triboelectricity of the surface it rubs against?

(Glass is one of the most positively triboelectric substances, and covers most solar panels. You can blame glass for the "wrong" direction of the charge convention. Ben Franklin was given a glass rod to conduct experiments on electricity, directly resulting in his choice of which charge is positive. Had he been sent a sulfur rod instead, the convention for current would be in the same direction as electron flow.)

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  • $\begingroup$ The top surfaces of solar panels on Mars might (or might not) be made of an oxide, but it might differ from the ordinary "glass" we think of when we hear the word. There are various kinds of doped deposited glasses and spin-on-glasses; is a real, separate sheet of ordinary glass exposed on the top surfaces of these panels? I just don't know. $\endgroup$
    – uhoh
    May 26, 2021 at 5:50
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    $\begingroup$ In the case of planet Earth: the surface of the Earth is negatively charged, the outer sphere - the ionosphere - is positively. The glass is positively polarized. It can be assumed that the situation on Mars is the same. And the charged dust particles are negatively attracted to the glass panels. $\endgroup$
    – A. Rumlin
    May 28, 2021 at 3:31
  • $\begingroup$ I had thought about the idea to repel dust with electrical energy after watching this video: youtube.com/watch?v=bK57JJ5MMCA then I saw that NASA had already made it for there space suits for the moon. youtu.be/0k9wIsKKgqo?t=735 Let me know if you have any more questions. $\endgroup$
    – William F Burroughs
    Jul 28, 2022 at 17:21

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The charge varies based on the size of dust particles. The small er particles tend to be negatively charged. Meanwhile, the larger ones tend to be positively charged.

From the April 20, 2004 NASA Goddard news item The Case of the Electric Martian Dust Devils (emphasis added by me):

Dust devil winds carry the small, negatively charged particles high into the air, while the heavier, positively charged particles remain near the base of the dust devil.

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