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Sparks on Mars

Electricity and magnetism · level 3, lesson 6 of 6

A question to start

Mars has no thunderstorms. But when scientists listened back to Perseverance's microphone, they heard sharp little cracks during dust devils. What was making them?

The idea

They were sparks. In a dust devil or at the front of a dust storm, billions of dry dust grains rub and bump together. They charge up, just like a balloon rubbed on hair. When enough charge builds up, it jumps: a spark.

Perseverance's microphone recorded 55 of these sparks over two Mars years, mostly in dust devils and dust storm fronts. Each spark was small, a few centimetres long, and close enough for the microphone to catch it. It was the first time anyone had detected electrical sparks on Mars.

Sparks form far more easily in Mars air, because it is so thin. In thin air, a much weaker push on the charges is enough to make the air start to carry them.

Making a spark in the air near the ground Mars Earth
How strong the electric push must be (the field, in kilovolts per metre) a few tens of kV/m about 3,000 kV/m
Big lightning in thunderstorms none seen yes
a tiny sparkthe microphone hears it

Worked examples

1. How much easier. A few tens of kV/m against about 3,000: sparks need roughly a hundred times less push in Mars air.

2. Why so dry matters. On Earth, damp air lets charge leak away. Mars air is far drier, so charge on the dust keeps building.

3. Heard, not seen. The sparks were found by the microphone: each left a sharp crack in the recording, along with a burst of electrical interference.

Try it

  1. What made the sparks Perseverance heard?
  2. How many sparks did it record, and over how long?
  3. Why do sparks form more easily in Mars air?
  4. Would an astronaut be in danger from these sparks?
Answers
  1. Dust grains rubbing together in dust devils and storm fronts, building up charge.
  2. 55, over two Mars years.
  3. The air is so thin that a much weaker push makes it carry charge.
  4. No, they were tiny, a few centimetres long. But charged dust could still affect equipment and suits.

Common mistake

"Mars has lightning storms." No big lightning has ever been seen. The sparks are small, in dusty air near the ground.

Where it leads