Scientists have confirmed the speed of sound on Mars, using equipment on the Perseverance rover to study the red planet’s atmosphere, which is very different to Earth’s.
An international team of researchers analyzing the sounds captured by the Perseverance rover has determined the speed of sound on Mars. Baptiste Chide, with Los Alamos National Laboratory, gave a presentation at this year’s 53rd Lunar and Planetary Science Conference outlining the findings by the team.
The findings suggest that trying to talk in Mars’ atmosphere might produce a weird effect, since higher-pitched sound seems to travel faster than bass notes. Not that we’d try, since Mars’ atmosphere is unbreathable, but it’s certainly fun to think about!
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The Perseverance rover landed successfully on the surface of Mars a little more than a year ago, and since that time, has been rolling around, studying the landscape with a host of cameras and sensors.
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The speed of sound is not a universal constant. It can change, depending on the density and temperature of the medium through which it travels; the denser the medium, the faster it goes.
Perseverance has also been outfitted with a microphone, which allowed the rover to beam back the first sounds ever heard from a distant world—many of those sounds can be heard on NASA’s Perseverance rover page. In this new effort, the researchers have been analyzing the sounds sent back by Perseverance to find out if they might reveal anything useful.
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That’s why sound travels about 343 meters (1,125 feet) per second in our atmosphere at 20 degrees Celsius, but also at 1,480 meters per second in water, and at 5,100 meters per second in steel.
Mars’ atmosphere is a lot more tenuous than Earth’s, around 0.020 kg/m3, compared to about 1.2 kg/m3 for Earth. That alone means that sound would propagate differently on the red planet.
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Chide reported that the team has used data from the microphone to measure the speed of sound on Mars. This was done by measuring the amount of time it took for sounds emanating from laser blasts from Perseverance to return to the rover’s microphone. The laser blasts were used to vaporize nearby rocks to learn more about their composition.
Conventional instruments for testing surface thermal gradients are highly accurate, but can suffer from various interference effects. Fortunately, Perseverance has something unique: microphones that can allow us to hear the sounds of Mars, and a laser that can trigger a perfectly timed noise.
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They found sound to be traveling on Mars at approximately 240 m/s. But they also found that different frequencies of sound travel at different speeds on Mars. The speed increases by approximately 10 m/s above 400 Hz. This finding suggests that communication would be extremely difficult on Mars with different parts of speech arriving to listeners at different times, making conversations sound garbled.
The SuperCam microphone was included to record acoustic pressure fluctuations from the rover’s laser-induced breakdown spectroscopy instrument as it ablates rock and soil samples at the Martian surface.
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This came with an excellent benefit, as it turns out. Chide and his team measured the time between the laser firing and the sound reaching the SuperCam microphone at 2.1 meters altitude, to measure the speed of sound at the surface.
“Therefore, at any given wavelength it is convoluted by the variations of temperature and wind speed and direction along this path.”
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Chide says the microphone also allowed for measuring temperature on Mar’s surface in and around the rover. This is because sound travels at different speeds depending on temperature. By measuring sound speed every time Perseverance fired its laser, the researchers were able to calculate rapid temperature changes.
The results back up predictions made using what we know of the Martian atmosphere, confirming that sounds propagate through the atmosphere near the surface at roughly 240 meters per second.
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“Due to the unique properties of the carbon dioxide molecules at low pressure, Mars is the only terrestrial-planet atmosphere in the Solar System experiencing a change in speed of sound right in the middle of the audible bandwidth (20 Hertz to 20,000 Hertz),” the researchers write.
Chide also noted that the research team plans to continue monitoring and analyzing sounds from Mars over the course of a year to learn more about fluctuations during different events on the planet, such as during the winter months or when dust storms kick up.
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At frequencies above 240 Hertz, the collision-activated vibrational modes of carbon dioxide molecules do not have enough time to relax, or return to their original state. The result of this is that sound travels more than 10 meters per second faster at higher frequencies than it does at low ones.
