Perseverance rover measures speed of sound on Mars for the first time

Using a laser to strike rocks and a built-in microphone, NASA’s Perseverance rover has measured changes in the speed of sound on Mars due to temperature affecting the atmosphere.

The speed of sound on Mars has been measured for the first time using microphones on NASA’s Perseverance rover.

Baptiste Chide at Los Alamos National Laboratory in New Mexico and his colleagues recorded sounds from the Mars’s Jezero crater last year, such as a laser striking rocks, which generates a shockwave. They also captured the frequency shift of the Ingenuity helicopter’s blades as it moved through the Martian atmosphere after launching from Perseverance.

The laser and microphone aboard Perseverance were precisely synchronised, so the researchers could use these recordings to calculate the speed of sound on Mars. It is about 240 metres per second, slower than the 340 metres per second at which sound travels on Earth.

The sound of speed on Mars also varied over small distances, which the researchers used to infer characteristics about the planet’s atmosphere, such as its temperature over small scales, which hadn’t been previously measured.

“We have a response time with acoustic measurements that is way faster than what we can achieve with standard and classical air temperature sensors,” says Chide.

The work, which was presented at the Lunar and Planetary Science Conference in Texas on 8 March, also revealed that the sound travelled in an unusual way in the Martian atmosphere, which is primarily low-pressure carbon dioxide. On Mars, higher frequency sounds arrive before the lower bass ones due to the way CO2 molecules vibrate differently at low and high frequencies.

“You would receive all the low frequencies of my voice a few milliseconds after the high frequencies… so it would lead to a kind of distortion of sounds that would be quite difficult to understand,” says Chide.

Chide and his team collected more than 5 hours of sounds in total, so are still poring over  the data to extract more information about Mars’s atmosphere. One area that they are interested in exploring is how the atmosphere and its temperature change with Martian seasons.

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