To guarantee future missions to Mars, especially with the presence of humans, it is necessary to understand the physics of some phenomena on the Red Planet. For example, the propagation properties of sound in the atmosphere. Studies have shown that sound travels at different speeds on Mars depending on the time of day. The new study makes it possible to estimate the speed of sound at any point on Mars at any time.

Several microphones have been installed on NASA’s Perseverance rover. It is necessary to study the properties of materials on Mars, but they provide insight into the sound background of the planet. For example, the rover recorded the sounds of a dust swirl. While deciphering the recordings, scientists found that sound waves with a frequency below 240 Hz propagate in the Martian atmosphere approximately 10 m/s slower than high-frequency sounds. This is due to carbon dioxide, the content of which is 95% in the air of Mars – it partially absorbs the energy of sound waves of low frequencies and slows down their propagation.

A group of scientists from the USA and France undertook to study in detail the propagation of sound in the Martian atmosphere within the first 20 m above surface level. Based on previously obtained data on conditions on Mars (temperature, pressure and carbon dioxide concentration), a model of the change in the speed of sound depending on these values ​​was compiled. Daily temperature drops of up to 60 °C and decreases in carbon dioxide concentration of up to 30% by volume are common on Mars. All of these are different, but they greatly change the speed at which sound propagates in the Red Planet’s air.

The calculations made it possible to draw many interesting conclusions, which were published in the journal JGR: Planets. The first is that dust does not seem to affect the propagation of sound the way it does on the ground. The change in the speed of sound with the change in temperature (about 0.5 m/s for every 1 °C) is similar to the dynamics observed on Earth.

What Earth doesn’t have is an extremely high concentration of carbon dioxide, and that’s what makes Mars different. But the biggest difference from Earth has to do with large daily temperature fluctuations. Against this background, carbon dioxide concentration is no longer such a determining factor. The rate of sound attenuation in the atmosphere during the hottest hour on Mars is three times greater than during the coldest hour. All together, they allowed scientists to create today’s most accurate model for estimating the speed of sound on Mars at any time of day, at any time of year, and at any point on the planet.

Finally, the proposed model will allow the interpretation of sounds recorded by the rover’s microphones, as they will actually record a distorted picture that needs to be corrected for an accurate evaluation.