What could conservation between two Earthlings look like on Mars? To something quite inaudible, if we are to believe a study published Friday, April 1 in the very serious review Nature. And for good reason, CNRS researchers reveal, thanks to the analysis of the sounds recorded by the Persévérance robot, that there are two speeds of sound (one for the treble and one for the bass) and a much stronger sound attenuation. on the red planet than on Earth.
The peculiarities of Mars
In general, sound is very different from one environment to another: temperature, altitude, materials, all characteristics having an impact on the nature of sound. In our atmosphere, at a temperature of 20 degrees ambient, sound travels through the air at 343 meters per second. But the red planet has other peculiarities that have an impact on the behavior of sound. Carbon dioxide molecules, subjected to low pressures (170 times less than on Earth), have “unique” properties that influence acoustic waves even within audible frequencies. As a result, on Mars, frequencies above 240 Hz travel faster than low frequencies. Clearly, high-pitched sounds come before low-pitched sounds. “This can induce a unique listening experience on Mars”, note the researchers.
The Perseverance robot records the first of sounds from Mars: the sound of the Ingenuity helicopter in flight
Special measures
The day after Perseverance landed, the microphone (of French design installed on the robot’s SuperCam) recorded the first sounds of the planet. “This first capture revealed turbulence regimes that were unknown until now,” says Sylvestre Maurice, astrophysicist at IRAP (French Institute for Research in Astrophysics), and co-responsible for the SuperCam. “But this passive listening was not telling enough. And since Mars is most of the time very quiet, it was necessary to use two active sound sources on board from Earth,” explained the astrophysicist. His team thus used the flights of the small Ingenuity helicopter, Perseverance’s traveling companion, and lasers fired at the rocks to probe their chemical composition (a clack clack noise). “We had a very localized source of sound there, between two and five meters away from its target, and from which we knew exactly when it was going to fire” explains the researcher.
The surprise came from the sound of the laser and its… 250 meters per second. “There, I panicked a little! I said to myself that one of the two measurements was wrong, because on Earth, near the surface, there is only one speed of sound,” explains Sylvestre Maurice. There are, however, two speeds: one for the treble (the laser), the other for the bass (the helicopter). “If we were 8 meters away on Mars, it’s as if we were talking 65 meters away on Earth”, compares Sylvestre Maurice. The discussions are indeed likely to be difficult.