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A massive dust swirl passed right over the Perseverance rover as it explored the site of an ancient lake on Mars – and the rover recorded the first sounds of this dust devil on Mars with his microphone.
Dust devils, or dust whirlwinds, are common on Mars and are part of the red planet’s weather patterns.
Other missions have collected images, weather data and dust measurements of these events, and NASA’s InSight lander has even recorded seismic and magnetic signals generated by the dust devils. But audio was the missing element — until now.
When the Perseverance rover landed on Mars in February 2021, it became the first mission to carry microphones on a trip to the red planet.
According to a new study published Tuesday in the journal Nature Communications, the robotic researcher’s SuperCam microphone was accidentally turned on and recording on Sept. 27, 2021, as a dust devil flew right over the rover.
During an 11-second clip captured by the microphone, there are two periods of low-frequency wind as the dust devil’s front and rear walls fly over the rover, said the study’s lead author, Dr. Naomi Murdoch, researcher at the University of Toulouse Higher Aerospace Institute.
Between the walls of the cyclone is a quiet time when the rover was in the eye of the cyclone, Murdoch said.
During the event, crackling and hissing can be heard, which were determined to be dust grains hitting the rover.
The researchers were able to count the particles in the dust devil as they hit the rover, leading to a whole new way of measuring the red planet, Murdoch said. It is the first time that an instrument has been able to quantify the dust thrown up on Mars.
Images and other data sent back by the rover also confirmed what happened. When the researchers put all the items collected by the rover together, they found that the dust devil was more than 118 meters tall and 25 meters wide – about 10 times larger than the rover itself. While that sounds like a massive whirlwind, it’s the average size for Dust devils from Mars, said Murdoch.
The researchers were surprised to find that dust was accumulating inside the dust devil, rather than just being carried into the outer walls — possibly because the dust devil may still have been in the process of formation when it moved across Perseverance.
Dust devils serve as indicators of turbulence in the atmosphere on Mars and play an important role in the Martian dust cycle.
Learning more about how dust kicks up and moves around the red planet – a key feature of its weather and climate, since dust is its main feature – can help scientists better understand how dust storms form and evolve.
A planet-orbiting dust storm ended the Opportunity Rover’s 15-year mission in 2018.
“Global dust storms are important for understanding the Martian climate,” Murdoch said. “The acoustic measurements of dust impact and dust uplift will therefore improve our understanding of dust devils and also help improve Martian climate models. Understanding dust elevation is also critical for space missions as it can damage hardware.”
Perseverance’s wind sensors have already been damaged by airborne dust particles, likely carried by the wind or a dust devil, Murdoch said.
Dust devils have a reputation for being both helpful and harmful on Mars.
The InSight lander’s mission is expected to end this month after spending four years studying earthquakes and other phenomena on the red planet. Layers of dust have accumulated on its solar panels, preventing the spacecraft from gathering enough power to continue operating its instruments.
Dust devils are common in Jezero Crater, where Perseverance landed, but they don’t appear to be present in InSight’s home on the flat plains of Elysium Planitia — and researchers aren’t sure why.
“With InSight, the dust from the atmosphere settled on the solar panels. However, since there are no hurricanes in the InSight region that can raise dust, the hurricanes are unable to ‘clean’ the solar panels.”
Other Mars missions have actually benefited from regular cleanings by dust devils, which acted like vacuum cleaners for the dust collected on the solar-powered Spirit and Opportunity rovers, giving them longer than expected lifespans.
The University of Toulouse’s Higher Aerospace Institute, known as ISAE-SUPAERO, built the microphone that sits atop Perseverance. Every month Murdoch and her team collect eight shots, each lasting about 167 seconds.
“We estimate that a single midday microphone observation (the time of day when most dust devil activity occurs) has only a 1 in 200 chance of picking up a dust devil like the one we encountered,” Murdoch said. “We were definitely lucky, but we also carefully targeted the instrument observations to increase the chances of success.”
More microphone recordings could capture additional dust devils, and Murdoch’s team is using acoustic recordings to measure atmospheric turbulence to determine their range on Mars.
The SuperCam microphone was originally included to listen as instruments on the Rover Zap rocks to determine their properties, but its acoustic data also sheds light on the red planet’s atmospheric science opportunities, Murdoch said.
“All of these measurements and analyzes show the value of acoustic data in planetary exploration. Therefore, at ISAE-SUPAERO we are developing in parallel the next generation of acoustic sensors that will be sent to other planetary bodies with an atmosphere in the future,” she said.