On September 27, 2021, NASA’s Perseverance rover was sitting on Mars, minding its own business, when it was suddenly engulfed by a dust devil that measured nearly 400 feet high and 80 feet wide.
Now, mission scientists have announced that Perseverance captured the eerie sound of this “chance encounter” with its SuperCam microphone, resulting in the first-ever audio recording of a dust devil on Mars, among many other unprecedented measurements, according to a new study. The newly released recording of the dust devil, which passed directly over Perseverance, is below.
Dust devils are swirling vortices that are incredibly common on Mars, yet remain mysterious for a number of reasons. For instance, it’s not clear why dust devils are abundant in some regions and scarce in others. Perseverance has detected many whirlwinds at its location on Mars, while another NASA mission, InSight, went a full year without sensing any. Scientists have also struggled to pin down the underlying dynamics of these events, which is important information when it comes to planning Martian surface missions.
Now, a team led by Naomi Murdoch, a planetary scientist at the National Higher French Institute of Aeronautics and Space (ISAE-SUPAERO) and the University of Toulouse, “describe the direct encounter of a dust-laden vortex with the Perseverance rover” which is an “entirely unique event,” according to a study published in Nature Communications on Tuesday.
“Within the team, we always knew that a microphone on Mars would be an important instrument for studying the Martian atmosphere and dust devils were one of the phenomena that we hoped to observe one day,” said Murdoch, who helped build the microphone, in an email to Motherboard. “However, to actually observe one is not simple; it requires careful planning and also good luck.”
“Dust devils typically manifest themselves as a distinctive drop in the atmospheric pressure data, often coincident with an abrupt change in wind direction,” she continued. “We knew for sure that we had successfully recorded a dust devil when we saw the pressure, wind, and sound recordings in parallel. There is only a 1 in 200 chance to detect such a dust devil with a single microphone recording in the mid-day period!”
As soon as the data reached Earth, Murdoch and her colleagues began the exciting work of characterizing the dust devil that briefly enveloped Perseverance. To their delight, Perseverance’s audio recording is so sharp that researchers were able to measure a key value, the flux of the wind-blown grains, for the first time ever.
In addition, the recording captured the patter of tiny grain impacts on the rover, and one loud “bang” that may have been a particularly large dust particle that pelted Perseverance.
“We can actually hear the noise of particles impacting the rover,” Murdoch said. “The sound of these impacts allows us to count how many particles were in the dust devil. This is a completely new measurement on Mars and demonstrates the potential of acoustic data for studying the dust lifting process on Mars.”
“The sound data was incredibly useful as it allowed us to determine almost immediately that the dust devil had passed directly over the rover,” she noted. “In the audio we can hear two periods of the low frequency wind as the dust devil leading and trailing walls pass over the rover, with a very calm period in between when the rover is in the eye of the vortex. The images from the rover’s navigation cameras quickly confirmed this first interpretation.”
The results will help scientists calibrate simulations of dust storms on Mars, especially the poorly understood “dust-lifting” process that sends particles spiraling off the surface into these whirlwinds. Such observations are key to unraveling the mysteries of the Martian climate and they will also play a practical role in improving weather forecasts that can inform future surface missions.
For instance, Murdoch noted that the abundance of dust devils at Perseverance’s landing site have damaged the rover’s wind sensors, while the scarcity of these whirlwinds at InSight’s location has allowed dust to accumulate on its solar panels. With no breeze to blow it off, this has consigned the poor probe to an early death as it is slowly starved of sunlight.
Moreover, the new study emphasizes the value of equipping space missions with microphones, so that they can listen in to the sounds of extraterrestrial frontiers.
“Within our team at ISAE-SUPAERO we were convinced that a microphone on Mars would be an important instrument for studying the Martian atmosphere and we haven’t been disappointed!” Murdoch said. “Since the SuperCam microphone recorded the first sounds on Mars in February 2021 the scientific importance of the sound data has been huge. This dust devil recording has demonstrated how useful a microphone can be for studying dust lifting and transport.”
“However, the SuperCam sound recordings also allow us to study the Martian wind at very fine scales (because we have such a rapid sampling rate) and to measure atmospheric turbulence in a range never observed before,” she concluded. “This dust devil sound and the other SuperCam microphone atmospheric recordings clearly demonstrate just how valuable acoustic data are in planetary exploration.”