NASA’s Perseverance rover, which has been examining the surface of Mars since February 2021, has for the first time registered the acoustic environment of the red planet. An international team1 led by an academic at the University of Toulouse III – Paul Sabatier and including researchers from CNRS and ISAE-SUPAERO, conducted an analysis of these sounds, obtained using the SuperCam instrument built in France under the direction of the French Space Agency CNES. Their results will be published on 1st April 2022 i Nature.
For 50 years, interplanetary probes have returned thousands of striking images of Mars’ surface, but never a single sound. Now, NASA’s Perseverance mission has put an end to this deafening silence by recording the first ever marching sounds. The scientific team1 for the French-American SuperCam2 instruments installed on Perseverance were convinced that the study of the soundscape of Mars could promote our understanding of the planet. This scientific challenge led them to design a microphone dedicated to the exploration of Mars, at the ISAE-SUPAERO in Toulouse, France.
Perseverance first recorded sounds from the red planet on February 19, 2021, the day after its arrival. These sounds fall within the human audible spectrum, between 20 Hz and 20 kHz. First of all, they reveal that Mars is silent, in fact so silent that scientists on several occasions believed that the microphone no longer worked. It is obvious that, in addition to the wind, natural sound sources are rare.
In addition to this study, the researchers focused on the sounds generated by the rover itself3, including the shock waves produced by the impact of the SuperCam laser on rocks and flights with the Ingenuity helicopter. By studying the distribution on Mars of these sounds, whose behavior is very well understood on Earth, they were able to accurately characterize the acoustic properties of Mars’ atmosphere.
Scientists show that the speed of sound on Mars is lower than on Earth: 240 m / s, compared to 340 m / s on our planet. The most surprising thing, however, is that it turns out that there are actually two sound speeds on Mars, one for high sounds and one for low frequencies.4. The 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. All of these different factors would make it difficult for two people standing just five feet apart to have a conversation. They depend on the composition of Mars’ atmosphere (96% CO2, compared to 0.04% on Earth) and the very low atmospheric surface pressure (170 times lower than on Earth).
After one year of the assignment, a total of five hours of recordings of the acoustic environment have been received. An in-depth analysis of these sounds has made the sound generated by the turbulence in the Martian atmosphere noticeable. The study of this turbulence, on scales 1,000 times smaller than anything previously known, should increase our knowledge of the atmosphere’s interaction with the surface of Mars. In the future, the use of other robots equipped with microphones can help us better understand planetary atmospheres.
1 Researchers from the following laboratories also participated: Institut de Recherche en Astrophysique et Planétologie (Université Toulouse III – Paul Sabatier / CNRS / CNES), Institut de Mécanique des Fluides de Toulouse (Université Toulouse III – Paul Sabatier / CNRS / INP), Laboratoire Spatial Studies and Astrophysical Instrumentation (Paris-PSL Observatory / CNRS / Sorbonne Université / Paris Cité University), Atmospheric Laboratory, Milieux, Spatial Observations (CNRS / Sorbonne Université / Université de Versailles-St Quentin Yvelines), Institut of Mineralogy, Physics of Materials and Cosmochemistry (CNRS / MNHN / Sorbonne University), Laboratory of Planetology and Geosciences (CNRS / University of Nantes / University of Angers), Institute of Planetology and Astrophysics of Grenoble (CNRS / University of Grenoble)), Center Lasers Intenses and Applications (CNRS / CEA / University of Bordeaux), Bordeaux Astrophysics Laboratory (CNRS / University of Bordeaux), Spatial Institute of Astrophysics (CNRS / University é Paris Saclay), Laboratory of Geology of Lyon: Earth, Planets, Environment (CNRS / ENS Lyon / Claude Bernard University) and Laboratory GeoRessources (CNRS / University of Lorraine).
2 SuperCam was jointly developed by LANL (Los Alamos National Laboratory, USA) and a consortium of laboratories affiliated with CNRS and French universities and research institutes. CNES is responsible to NASA for the French contribution to SuperCam.
3 The microphone also acts as a stethoscope for the rover as it provides an acoustic diagnosis of its health.
4 Approximately 240 m / s for frequencies below 240 Hz and 250 m / s above