NASA’s Perseverance rover has for the first time captured the low-pitched whirring of the Ingenuity helicopter’s blades as it flies through the rarefied Martian atmosphere.
The space agency released footage shot by the six-wheeled robot of its rotorcraft companion making its fourth flight on April 30, accompanied by an audio track.
The nearly three-minute-long video begins with the low rumble of wind blowing across the Jezero Crater, where Perseverance landed in February on a mission to search for signs of ancient microbes.
🔊🔴 New sounds from Mars: Our @NASAPersevere rover caught the beats coming from our Ingenuity #MarsHelicopter! This marks the first time a spacecraft on another planet has recorded the sounds of a separate spacecraft.
— NASA (@NASA) May 7, 2021
Ingenuity takes off, and its blades can be heard humming softly as they spin at nearly 2,400 rpm on the 872-foot roundtrip.
The mission’s engineers weren’t sure they would pick up the flight sound at all, given that Perseverance was parked 262 feet away from the takeoff and landing spot.
The Martian atmosphere is about one percent the density of our planet’s, making everything much quieter than on Earth.
“This is a very good surprise,” said David Mimoun, a professor of planetary science at Institut Superieur de l’Aeronautique et de l’Espace (ISAE-SUPAERO) in Toulouse, France, and science lead for the SuperCam Mars microphone.
“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,” he added.
The SuperCam is an instrument on board Perseverance that laser-zaps rocks from a distance, in order to study their vapor with a device called a spectrometer that reveals their chemical composition.
It also comes with a microphone to record the sounds, which yields additional insights into the physical properties of the targets, like how hard they are.
Apart from having a lower volume, sounds emitted on Mars travel slower than they do on Earth, because of cold temperatures, which average -81 degrees Fahrenheit (-63 degrees Celsius) on the surface.
The speed of sound on the planet is therefore around 540 mph compared to about 760 mph here.
The atmosphere of Mars, made up of 96 percent carbon dioxide, tends to absorb higher-pitched sounds, so only lower-pitched sounds can travel long distances.