A catalogue of Martian sound

Introduction

The two microphones onboard the Perseverance rover have now been operating for more than three years on the surface of Mars. They have provided the first sound recordings at the Martian surface and the most extensive acoustic dataset recorded on another planet.  The Martian microphones have recorded sound waves, and more generally signals, from a wide variety of sources. Given the novelty of this dataset, we felt the need for a catalogue of Martian sounds. This catalogue contains a description of every type of sound both from an individual and a statistical perspective. This allows us to highlight the particular characteristics of each of the sources that can be retrieved from recording their sounds, including possible variations over time for recurring recordings. Using this catalogue, we also discuss scientific applications for each of the sound sources, highlighting how useful microphone data are to survey the Martian environment. Finally, the catalogue serves as a starting point for newcomers by demonstrating how to use the acoustic data and explaining which features of the recordings are already well understood and identifying others that are still open to investigation.

The Martian microphones

Two microphones are operated onboard the Perseverance rover. The SuperCam Microphone [1], located on the mast unit, operates in two modes, the MIC only mode where up to 167 s of sound at 25 kHz can be recorded, and the MIC+LIBS mode that record the shots of the LIBS instrument. More than 24 hours of recording have been acquired in the first mode and more than 6000 LIBS sequences have been recorded in the second one. The EDLCam microphone [2], located on the side of the rover body, can record for longer period of times at 48 kHz. More than 12 hours of recordings, mainly rover sound, have been acquired.

Both microphones are subject to operational constraints that shape the resulting dataset.

Environment sound sources

While not being strictly speaking a sound, the signal coming from the interaction between the wind and the microphone is always present on the recording at different levels. This allows the microphone to act as a high frequency wind sensor [3]. The spectra of the wind recording contain information about atmospheric turbulence near the Martian surface [4], which can be studied at different times of year and day thanks to the regular coverage offered by the microphone’s dataset.

The microphone-derived wind signal has been used to resolve the properties of a dust devil that was recorded during a rare direct encounter with the rover. During this event [5] the sound of the dust grains carried by the vortex impacting on the rover were also recorded, allowing an estimation of their number density.

Artificial sound sources

Sound recording around every LIBS shot contains information about the sound wave travel times and energy that can be used to study the temperature fluctuation [6] and the atmospheric turbulence [7]. This is made possible through the speed of sound and the scintillation measurements at different times of year thanks to the almost daily coverage in LIBS sound recording. Other artificial sounds such as the Ingenuity helicopter [8] or the operation of different parts of the rover (driving, drilling, abrading, MOXIE compressor [9], pumping of the heat rejection system fluid) were also recorded. These data were used to study the acoustic properties of the Martian atmosphere [10] and to monitor the health of the rover systems.

Conclusion

After three years at the Martian surface, Perseverance has sent back to Earth a rich dataset of acoustic recordings that has already yielded numerous scientific results. As it continues its journey at the surface of Mars, we expect that the microphones will bring greater detail to the established results as well as leading to new discoveries. Moreover, lessons learned on this mission will be useful for future acoustic experiments on other planetary bodies [11, 12].

 

[1] Mimoun et al. (2023) Space Science Reviews, 219 [2] Maki et al. (2020) Space Science Reviews [3] Stott et al. (2023) JGR : Planets [4] Stott et al. (2024) 10th International Mars Conference [5] Murdoch et al. (2022) Nat. Commun. [6] Chide et al. (2022) GRL [7] Chide et al. (2024) J. Acoust. Soc. Am. 155, 420–435.  [8] Lorenz et al. (2023) Planetary and Space Sciences 230.  [9] Hecht et al. (2021) Space Science Review [10] Chide et al. (2023) Earth and Planetary Science Letters 615 [11] Barnes et al. (2021) The Planetary Science Journal,2,4 [12] Gillier et al. (2024) IPPW