The speed of sound on Mars is kinda awesome, according to new evidence

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A selfie taken by NASA's Perseverance rover on September 10, 2021.

A selfie taken by NASA’s Perseverance rover on September 10, 2021.
Picture: NASA/JPL-Caltech/MSSS

Using a microphone, a laser and some nifty math, a team of scientists have measured the speed of sound on Mars, in what is a scientific first and another interesting discovery made possible by the Perseverance rover. from NASA.

There’s a lot to like about the Perseverance mission, but one of my favorite things about the rover is that it’s able to record audio.. Early last year, for the very first time, we were able to hear sounds on Mars, both natural and synthetic. By using his Micro Super Camthe rover checked in blowing Martian winds, clicks of its rock-scanning laser and the creaking sounds emitted by its rolling wheels.

Whether Perseverance’s microphone picked up these sounds was not certain, given the red planet’s extremely thin atmosphere. Sound needs a medium to propagate, and Mars, with a derisory atmospheric pressure of 0.095 pounds per square inch (psi) at ground level, doesn’t offer much to work with. In comparison, atmospheric pressure at sea level on Earth is about 14.7 psi.

But they were there—perceptible noises picked up by Percy’s microphone in Jezero Crater. With clearly audible sounds on Mars, Baptiste Chide of the Los Alamos National Lab in Los Angeles and colleagues were capable of measuring the speed of sound on Mars. Scientists recently presented their results to 53rd Lunar and Planetary Science Conferenceheld March 7-11 in Texas.

the team leveraged Perseverance’s SuperCam experiment, which zaps rocks with lasers to study Martian geology and sits at the top of the rover’s mast about 6.9 feet (2.1 meters) above the Martian surface. The team took measurements from 150 laser shots taken at five separate locations, while monitoring local weather conditions.

By measuring how long it took for jerky clicking sounds to reach the SuperCam microphone, they were able to establish the speed of sound on Mars, with an accuracy of plus-minus 0.51%. They found that sound on Mars travels at 787 feet per second (240 meters per second), which is significantly slower than speed sound on Earth at 1,115 feet per second (340 m/s).

And in an observation that matched earlier predictions, the speed of sounds below 240 hertz dropped to 754 feet per second (230 m/s). This does not happen on Earth, because sounds in the audible bandwidth (20 Hz to 20 kHz) travel at a constant speed. The “idiosyncrasy of Mars”, as scientists call it, is linked to the “unique properties of carbon dioxide molecules at low pressure”, which make the Martian atmosphere the only one in the solar system to experience “a change of sound just in the middle of the audible bandwidth,” as the scientists wrote. The reason for this is that sounds above 240Hz don’t have time to release their energy, the scientists say.

The scientists go on to say that this acoustic effect “could induce a unique listening experience on Mars with an earlier arrival of high-pitched sounds relative to low-pitched sounds.”

Unique is right! Much acoustic information exists below 240 Hz, including the low end of music and the lowest registers of the human voice (usually for males). Music on Mars would sound completely messed up (especially with increased distance), with mid and high frequencies reaching the listener slightly before low frequency sounds, such as the lower registers of bass guitar and kick drum. Add another effect of carbon dioxide, the attenuation or damping of higher frequencies, and the acoustic experience becomes even weirder.

Incidentally, the technique used to measure the speed of sound can also be used to measure local temperature. So in addition to Percy Mars Environmental Dynamics Analyzer (MEDA), the team has a new thermometer. Looking ahead, Chide and his colleagues will perform more tests to measure the speed of sound at different times of day and during different Martian seasons.

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