NASA’s Perseverance hasn’t just been working as camera-rover for the Insight Mars helicopter, but also capturing audio of the historic aircraft as it flies above the red planet’s surface, the space agency has revealed. During Ingenuity’s fourth flight, which took place at the end of April, Perseverance was both capturing video and audio, which NASA has released today.
The microphone itself is part of Perseverance’s SuperCam laser instrument, and isn’t really there to record the sound of Martian flight. Instead, the SuperCam uses a laser to vaporize small amounts of rock sample, which are then analyzed by a spectrometer to deduce their chemical composition: the microphone records the sound of the laser’s effect, to help calculate factors like overall hardness.
However it can also be activated separately, to record things like the wind noise on Mars. It’s through that background hubbub that Perseverance picked up the sound of Ingenuity’s helicopter blades, even though the two were 262 feet apart. NASA’s Jet Propulsion Lab – responsible for running the Perseverance mission – parks the rover at a safe distance from Ingenuity during its flight tests, so as to reduce the risk of inadvertently damaging it should a crash occur.
Still, even at that distance, you can hear the faint hum of the helicopter as it takes off and flies.
“We had carried out tests and simulations that told us the microphone would barely pick up the sounds of the helicopter, as the Mars atmosphere damps the sound propagation strongly,” David Mimoun, science lead for the SuperCam Mars microphone, explains. “We have been lucky to register the helicopter at such a distance. This recording will be a gold mine for our understanding of the Martian atmosphere.”
It did take a little post-processing to coax out the audible detail, mind. The microphone captures audio in mono, and the JPL team isolated the specific frequency of the helicopter blade sound – at 84 hertz – by reducing anything below 80 hertz or above 90 hertz. “Some frequencies were clipped to bring out the helicopter’s hum,” NASA says, “which is loudest when the helicopter passes through the field of view of the camera.”
It’s not the first time we’ve heard details from Mars using microphones mounted on Perseverance. Shortly after the rover touched down on the red planet, it sent back a cache of early recordings – including both photos and video – as its initial equipment began the process of coming online.
Having nailed its initial flight goals, Ingenuity will now be accompanying Perseverance to a new area of Jezero Crater on Mars. There it’ll be used to support future scientific missions, including giving the rover operators an aerial insight into what areas might be of most interest for the rover’s various onboard instruments.