The trove of data coming from the encounter has thrilled scientists, who are keenly aware of the outsize influence Martian dust has on the planet’s climate. The fine-grained particles also can damage scientific instruments on Martian landers and rovers and potentially blanket solar panels to the point of uselessness. Studying the rover’s gritty recordings can provide insights into the way dust might affect ongoing Mars missions, and maybe even future human exploration.
The sound of the dust devil, published Tuesday to accompany a paper in the journal Nature Communications, is subtle. It’s crackly and percussive, like radio static, though one might more generously imagine a breeze ruffling some distant palm fronds.
Then come a few seconds of silence as the eye of the dust devil passes over the rover. Sound returns for another couple of seconds as the trailing wall of the dust devil spins over the rover again. Then it’s all over, and Mars is quiet once more.
This was not exactly an “extreme weather” event. Mars has a trifling atmosphere, about 1 percent as dense as Earth’s, so the storms there don’t howl. The rover suffered no damage.
Still, there is plenty of signal in this short dose of noise, and in the visual images taken by the SuperCam instrument on top of the rover. Researchers estimate the dust devil was about 25 meters (82 feet) wide and 118 meters (387 feet) high. That’s taller than the Statue of Liberty, pedestal included.
“As the dust devil passed over Perseverance we could actually hear individual impacts of grains on the rover,” said Naomi Murdoch, a planetary scientist at ISAE-SUPAERO, an aerospace engineering institute in Toulouse, France, and the author of the new report. “We could actually count them.”
A dust devil is a bit like a miniature storm cell. It typically pops up during the middle of the day as hot air spirals up from the surface. A scientist wishing to speak more technically could call this a convective vortex loaded with dust. The dust is not the cause of the vortex, but is just along for the ride.
Murdoch said the team’s success in capturing a dust devil’s sound reflects both luck and preparation. The rover’s microphone takes recordings lasting a little under three minutes, and it does that only eight times a month. But the recordings are timed for when dust devils are most likely to occur, and the rover cameras are pointed in the direction where they are most likely to be seen.
“Then we have to just cross our fingers,” she said.
That clearly did the trick, because Perseverance managed to capture the dust devil through multiple instruments, registering the drop in air pressure, changes in temperature, the sound of grains making impact, all topped off with images that show the size and shape of the vortex.
“I can’t think of a previous case where so much data from so many instruments contributed to characterizing a single dust devil,” John Edward Moores, a planetary scientist at York University, said in an email after reviewing the new paper. He said the team was fortunate to have all the observations overlap.
“Had the [camera] been pointing in a different direction or the microphone observation been scheduled just a few seconds later, key pieces of the story would be missing. Sometimes it helps to be lucky in science!”
While the Perseverance team is cheering their windy encounter, calm weather has become a problem for a different NASA robotic craft on Mars. The InSight lander, which touched down more than 2,000 miles away in November 2018, has instruments to explore seismicity and the interior of the planet.
InSight has lasted a couple of years beyond its primary mission timeline but now is in the final weeks of its scientific life because its solar panels are 90 percent covered with dust. What it needs is a direct hit by a dust devil, because such vortices are capable of cleaning solar panels.
“A dust devil is like a little vacuum cleaner running over the surface,” said Bruce Banerdt, a planetary geophysicist at the NASA Jet Propulsion Laboratory and the principal investigator for InSight.
But InSight hasn’t gotten a visit from a devil capable of cleaning its arrays. Banerdt said currently there is enough power to run a seismometer for eight hours, but then it has to rest for three days while the batteries recharge.
“We’re still limping along at this point,” he said.
Murdoch said this scattershot pattern of dust devils appearing on Mars remains mysterious. Planetary scientists also can’t predict when the Red Planet will have a global dust storm, she said, citing “our poor understanding of precisely how and when dust is lifted from the surface of Mars.”
But that’s changing, she hopes, as the microphone her team developed continues to listen to the sounds of that distant desert planet.