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What the microphones heard

Waves, sound and light · level 4, lesson 5 of 6

A question to start

Perseverance made the first recordings of sound on the surface of Mars. What did it hear, and why would scientists want to listen to a planet?

The idea

Perseverance's main microphone sits on its mast, as part of the SuperCam instrument. In its first year it recorded hours of Mars sounds:

  • The wind. Gusts and turbulence, which tell scientists how the air near the ground swirls and mixes.
  • Laser sparks. SuperCam fires a laser at rocks to study them. Each zap makes a crack, and its loudness hints at how hard the rock is.
  • Ingenuity. The helicopter's rotors hummed at about 84 Hz, with a second tone at 168 Hz.
  • A dust devil. On 27 September 2021, one passed right over the rover. The microphone heard the wind and the patter of dust grains hitting the rover.
  • The rover itself. Its heat pump, which keeps it at the right temperature, hums at about 195 Hz.

Some of the recordings are very quiet indeed.

microphonelaser zaphelicopter

Worked examples

1. The heat pump's note. 195 Hz is below 240 Hz, so it is in the "low" group and travels at about 240 m/s.

2. A second tone. 168 Hz is exactly twice 84 Hz. Musicians call it the first overtone, an octave above.

3. Timing the helicopter. By comparing when sounds arrived, and how their pitch shifted as Ingenuity moved, the scientists could measure the speed of sound for low notes.

Try it

  1. Where is Perseverance's main microphone?
  2. What can the sound of a laser zap tell scientists about a rock?
  3. Ingenuity's second tone was at 168 Hz. How is it related to the first?
  4. Why is listening to the wind useful to scientists?
Answers
  1. On its mast, as part of SuperCam.
  2. Its loudness gives a hint of how hard the rock is.
  3. It is exactly twice the frequency: an octave higher.
  4. It shows how the air near the ground swirls and mixes.

Common mistake

"The microphones are just for fun." They are science tools: they measure the speed of sound, the turbulence of the wind, and the hardness of rocks.

Where it leads