This is what humans have learned about sound on Mars

In this April 30, 2021, file image taken by the Mars Perseverance rover and made available by NASA, the Mars Ingenuity helicopter, right, flies over the surface of the planet. (NASA/JPL-Caltech/ASU/MSSS via AP, File)

Interplanetary spacecraft have returned hundreds of stunning photographs of Mars' surface over the last 50 years, but not a single sound. That’s all changed thanks to NASA's Perseverance rover.

A new study, based on recordings made by its Perseverance rover and published in the journal Nature, has found that the speed of sound is slower on Mars than on Earth, and that the planet is mainly silent.

The research team behind Perseverance's French-U.S. SuperCam2 equipment was persuaded that studying Mars' soundscape may help us better comprehend the planet. So the team in Toulouse, France, designed a microphone dedicated to the exploration of Mars in response to this scientific challenge.

The first sounds from Mars were captured by Perseverance on Feb. 19, 2021, the day after it arrived. Between 20 Hz and 20 kHz, these sounds come inside the human auditory range. They demonstrate that Mars is silent, so quiet that scientists mistook the microphone for broken on multiple occasions.

The study states that apart from the wind, natural sound sources are rare. In addition to this, the scientists investigated the sounds produced by the rover itself, such as shock waves caused by the SuperCam laser's impact on rocks and flights by the Ingenuity helicopter.

They were able to precisely characterize the acoustic features of the Martian atmosphere by investigating the propagation on Mars of these sounds. The behaviour of which is well understood on Earth.

The researchers discovered that the speed of sound on Mars is slower than on Earth: 240 m/s against 340 m/s on our planet. The most striking discovery is that there are two different rates of sound on Mars, one for high-pitched noises and the other for low frequencies.

On Mars, sound attenuation is stronger than on Earth, particularly for high frequencies, which, unlike low frequencies, attenuate rapidly even over short distances, the study states.

All of these elements would make it difficult for two people standing merely five metres apart to be able to have a conversation and hear each other.

The study states that this is caused by the Martian atmosphere's composition (96 per cent CO2, compared to 0.04 per cent on Earth) and the extremely low atmospheric surface pressure (170 times that of Earth).

After a year on the mission, a total of five hours of auditory environment recordings were acquired.

The sound produced by the turbulence of the Martian atmosphere has become perceptible thanks to an in-depth analysis. The study of this turbulence, at scales 1,000 times smaller than anything previously known, might help us better understand how Mars' atmosphere interacts with its surface.

Other robots with microphones might be used in the future to help us better comprehend planetary atmospheres.