Nasa’s Perseverance rover has recorded what is believed to be the first-ever Martian sounds.
Perseverance made its first sound recording on Mars on 19 February, the day after its arrival. These sounds fall within the human audible spectrum, between 20Hz and 20kHz.
Despite the recordings, Mars is thought to be very quiet, with the team mistakenly believing that the microphone was no longer working on several occasions as it failed to pick up any noise. Apart from the wind, natural sound sources are rare.
The team has also been focusing on the sounds generated by the rover itself, including the shock waves produced by the impact of the SuperCam laser on rocks and flights by the Ingenuity helicopter.
By studying the propagation on Mars of these sounds, whose behaviour is well understood on Earth, they were able to accurately characterise the acoustic properties of the Martian atmosphere.
The researchers show that the speed of sound is lower on Mars than on Earth: 240m/s, as compared to 340m/s on our planet. However, the most surprising thing is that it turns out that there are actually two speeds of sound on Mars, one for high-pitched sounds and one for low frequencies.
Sound attenuation is greater on Mars than on Earth, especially for high frequencies, which unlike low frequencies are attenuated very quickly, even at short distances.
This is due to the composition of the Martian atmosphere (96 per cent CO2, compared to 0.04 per cent on Earth) and the very low atmospheric surface pressure (170 times lower than on Earth).
After one year of the mission, a total of five hours of recordings of the acoustic environment have been obtained. In-depth analysis of these sounds has made the sound generated by the turbulence of the Martian atmosphere perceptible.
The study of this turbulence, at scales 1,000 times smaller than anything previously known, should enhance knowledge of the interaction of the atmosphere with the surface of Mars.
In the future, the use of other robots equipped with microphones could help scientists to better understand planetary atmospheres.
Perseverance collected its first sample of Martian rock from the planet’s surface in September 2021, having made its landing on the planet’s surface in the previous February.
The rover will spend the coming years scouring for signs of ancient microbial life in a mission that will bring back samples to Earth and prepare the way for future human visitors.