How researchers first recorded the sounds of a Martian dust devil

On September 27, 2021, a heck of a dust flew over the Perseverance rover to Mars. Not only did the rover capture the dust devil with its cameras and weather sensors, it also picked up the dust devil’s faint, eerie sounds on its microphone, the first instrument of its kind to record sounds on Mars.

“We were convinced that the microphone would give us a whole load of new observations of atmospheric features on Mars that we hadn’t been able to see before,” Naomi Murdoch of the University of Toulouse, lead author of a Nature communications paper on research, said a The limit. “And we weren’t disappointed!”

Rovers have been exploring Mars for decades with cameras, spectrographs and weather sensors, giving us a better picture than ever of what the environment is like on the Red Planet. Now, the sounds are added to the list. This combination of data is enabling researchers to better understand these dusty phenomena and the impacts they could have on future manned and robotic missions.

Dust devils arise due to the atmospheric conditions common on Mars. “You have to have a really large temperature gradient between the ground and the air,” Murdoch explained. “So the ground gets really hot, and that heats the air, which then makes the air rise. And when the air starts to rise, things start to rotate, and that’s when you get this vortex-like motion.

This process happens here on Earth as well, but what’s remarkable about Martian dust devils is how big they can get. The dust devil recently detected by Perseverance was 25 meters wide and 118 meters high (82 feet by 387 feet), placing it squarely in the middle range in size for Martian dust storms. But they can also get much bigger, as dust on Mars can be kicked up in massive global dust storms.

“One of the big problems we have right now is that we can’t predict dust storms very well,” Murdoch said. And that has implications for everything from trying to land a spacecraft safely on Mars to trying to keep dust off solar panels vital to keep robotic missions going. Current models have a particularly hard time predicting large global dust storms, and this appears to be because it is difficult to model the forces that are kicking up dust from the planet’s surface.

Researchers know that forces like wind shear and dust devils can lift dust off the surface, but there are many open questions about exactly how this happens. One particularly strange finding is that while dust devils are common in the Jezero crater where Perseverance is located, they are especially rare in Elysium Planitia, the area where the InSight lander is located, and it’s unclear why.

This is where the microphone comes into play. “What our microphone is sensitive to specifically is wind speed. So when we see gusts of wind, we see a big increase in the amplitude of the sound at the microphone, just like when you’re talking on the phone and it’s windy,” Murdoch explained. “We’re using that background noise to study wind.”

With so many scientific instruments on Perseverance requiring uptime, the windows available for microphone recordings are only a few minutes each. To maximize their chances of detecting a dust devil during these short periods, the microphone team timed those windows for the afternoon periods when the dust devils are most active. Each window only lasts a few minutes and they only had eight windows a month, so it was a combination of careful planning and a good deal of luck that this recent dust devil got caught.

In addition to gathering data on wind conditions, the microphone also picked up the sound of small impacts – individual specks of dust hitting the area around the microphone and producing a detectable ping. By counting each of these impacts, the researchers were able to see how dense these particles were inside the dust devil, a measurement that no other instrument has been able to make and which could help model how dust devils kick up their bodies. particles from the surface.

This research is just a first example in the burgeoning field of using acoustic data in planetary exploration. For a planet or moon with an atmosphere, acoustic instruments can collect data at a high sample rate, allowing for observations of rapidly changing events such as wind gusts compared to instruments such as wind sensors, which operate on scales thunderstorms of a few seconds.

“Our sample rate is much higher than all the regular weather sensors you’ll find on planetary rovers and planetary landers,” Murdoch said. “With a microphone it’s a bit like using a microscope. We’re looking at what’s happening on these really short timescales.

There is also the human fascination that comes with hearing the sounds of another planet. NASA’s Perseverance Sounds Playlist allows anyone to experience the sounds of the Red Planet, from the hiss of the wind to the hum of the rover itself, all enabled by the SuperCam’s microphone.

“The bandwidth of our microphone is exactly the same as the human ear, so the sounds we hear are not adjusted in any way. Those are the sounds you would hear if you were on another planet,” Murdoch said. “And that’s pretty awesome.”