The sound of a Martian dust devil

Dust devils, convective vortices laden with dust, are prevalent on Mars, especially at Jezero crater, the Perseverance rover's landing site. They are key indicators of atmospheric turbulence and play a crucial role in the Martian dust cycle, a significant factor in the planet's climate and surface processes. Understanding dust lifting and atmospheric transport is vital for accurate climate modeling and predicting dust storms, crucial information for planning future space exploration missions. Grain impacts from dust devils also contribute to the degradation of surface hardware. This study presents, for the first time, the sound of a Martian dust devil recorded by the SuperCam microphone on the Perseverance rover. By integrating this acoustic data with simultaneous observations from the rover's Navigation Camera and the Mars Environmental Dynamics Analyzer (MEDA), the researchers aimed to characterize the dust devil's properties and improve our understanding of Martian atmospheric processes.

Previous research has extensively documented the presence and characteristics of Martian dust devils using various observational techniques. Studies based on images from orbiters and landers have revealed their abundance and spatial distribution. In situ measurements from landers like InSight have provided data on pressure fluctuations and wind speeds associated with dust devil passages. Theoretical models and simulations have attempted to understand the formation and dynamics of these vortices. However, direct measurements of particle flux associated with dust lifting, crucial for refining climate models, have been lacking. The use of acoustic data to study atmospheric processes on Mars was a relatively unexplored area, with the SuperCam microphone providing a novel opportunity to address this gap.

The study utilized a unique dataset combining acoustic data from the SuperCam microphone, visual data from the Navigation Camera (Navcam), and meteorological data from MEDA on the Perseverance rover. The SuperCam microphone recorded air pressure fluctuations at a high sampling rate, capturing the rapid wind variations associated with the dust devil passage. The Navcam images provided visual information on the dust devil's size and trajectory. MEDA instruments, including barometers, wind sensors, temperature sensors, and a radiation and dust sensor (RDS), offered complementary meteorological data. The researchers developed a model of the vortex pressure profile and used Monte Carlo simulations to refine dust devil parameter estimates (diameter, core pressure drop, trajectory, translation speed, rotation direction, closest approach distance, and vortex height). The acoustic data were analyzed to identify and quantify grain impacts, providing information on particle number density within the vortex. The researchers compared model-generated synthetic data with the actual measurements from various sensors to validate the derived dust devil parameters. Analysis of the acoustic signals, including identification of grain impacts and a loud, broadband “bang” also provided insights into the vortex's particle content and the nature of grain interactions with the microphone.

The analysis revealed that the dust devil was approximately 25 meters in diameter, at least 118 meters tall, and traveled at about 5 meters per second. The core pressure drop was measured to be approximately 2 Pa. The acoustic data revealed three bursts of grain impacts, totaling 308 impacts, with a mean impact frequency of 60 impacts per second. The highest observed impact frequency suggests a maximum of 27 grain impacts per meter within the vortex, indicating a relatively low dust content, consistent with RDS measurements and Navcam images. The researchers found a strong match between the modelled and observed pressure and wind direction data. The asymmetry in the sound amplitude's RMS was captured by the synthetic model, confirming the offset between background wind and dust devil trajectory. A prominent, broadband acoustic signal, likely resulting from a close impact of a large particle, was observed. The analysis suggests that this dust devil passed directly over the rover, with the microphone recording the distinct acoustic signatures of the leading and trailing vortex walls, as well as the relatively calm 'eye' of the vortex in between.

The successful recording and analysis of a Martian dust devil's acoustic signature, combined with multi-sensor data, provides unprecedented insights into these atmospheric phenomena. The acoustic data offer a high-resolution view of the rapid wind structure within the vortex, complementing lower-frequency measurements from other sensors. The ability to directly quantify wind-blown grain fluxes is a key advance, offering critical data to validate and improve Martian climate models. The observation of grain impacts opens up new avenues for studying Martian saltation and dust lifting, critical processes for understanding surface change and climate variability. This research demonstrates the importance of acoustic data in planetary science research and offers the prospect of applying acoustic monitoring to study the effects of dust devils on future hardware.

This study provides the first-ever acoustic recording of a Martian dust devil, demonstrating the power of acoustic data to complement traditional observational techniques. The detailed characterization of the dust devil's properties and the quantification of grain impacts offer critical information for refining Martian climate models and understanding aeolian processes. Future research could focus on expanding this methodology to study dust devils in different Martian locations and under diverse atmospheric conditions. Additional laboratory work to establish relationships between grain impact kinetic energy and microphone output could enhance the quantitative capabilities of this approach. Further analysis could help to improve instrumentation designs to minimize the detrimental effects of dust devils on surface equipment and operations.

The study's findings are based on a single dust devil encounter. While the probability of observing such an event was calculated, more observations are needed to generalize the findings. The identification of grain impacts relied on an algorithm originally developed for terrestrial environments; further research may be needed to adapt this technique for the unique acoustic properties of the Martian atmosphere. The interpretation of Navcam images to determine dust devil parameters involved some subjective judgments.