According to scientists, the first audio recordings from Mars depict a peaceful planet with periodic gusts of wind where two differing speeds of sound would have a weird delayed effect on hearing.
After NASA’s Perseverance rover landed on Mars in February of last year, its two microphones began recording, allowing scientists to hear for the first time what it’s like on the Red Planet.
The scientists released their first analysis of the five hours of sound picked up by Perseverance’s microphones in the journal Nature on Friday.
According to Sylvestre Maurice, the study’s principal author and scientific co-director of the shoebox-sized SuperCam installed on the rover’s mast, which contains the main microphone, the audio showed previously unseen turbulence on Mars.
The international crew listened to flights by the tiny Ingenuity helicopter, a sister craft to Perseverance, and heard the rover’s laser zap rocks to investigate their chemical composition, which made a “clack clack” sound, according to Maurice.
He explained: “We had a very localized sound source, between two and five meters (six to 16 feet) from its target, and we knew exactly when it was going to fire.”
The study proved for the first time that the speed of sound on Mars is slower, traveling at 240 meters per second compared to 340 meters per second on Earth.
This was expected because Mars’ atmosphere contains 95 percent carbon dioxide (compared to 0.04 percent on Earth) and is nearly 100 times thinner, making sound 20 decibels softer, according to the study.
However, the scientists were taken aback when the laser’s sound reached 250 meters per second—10 meters quicker than expected.
“I freaked out a little,” Maurice admitted. “I convinced myself that one of the two measurements was incorrect because there is only one speed of sound on Earth.”
They’d uncovered two speeds of sound on Mars’ surface: one for high-pitched sounds like the laser’s zap, and another for lower frequencies like the helicopter rotor’s whir.
This indicates that high-pitched noises would be heard significantly earlier by human hearing.
On Earth, whether the sounds are low or high, they reach you at the same rate. However, on Mars, if you are a little too far from the stage, there will be a significant delay. According to Maurice,
“All of these elements would make it difficult for two people only five meters (16 feet) away to have a discussion,” the French CNRS research institute said in a statement.
A “scientific gamble” pays off.
Otherwise, Mars was so quiet that scientists repeatedly worried that something was wrong, according to the CNRS, possibly triggering memories of two previous failed attempts to record sound there in 1999 and 2008.
In a statement released in conjunction with the study, the scientists stated, “With the exception of the wind, there are few natural sound sources.”
According to the investigation, the microphones picked up several “screech” and “clank” sounds as the rover’s metal wheels clashed with pebbles.
The recording could also warn about rover difficulties, similar to how drivers notice something is wrong when their automobile starts making weird noises.
Maurice declared that the “scientific gamble” of sending microphones to Mars had been a success.
Listening to turbulence, such as vertical winds known as convection plumes, would “enable us to update our numerical models for predicting climate and weather,” according to Thierry Fouchet of the Paris Observatory, who was also engaged in the research.
Future expeditions to Venus or Saturn’s moon Titan may now include microphones.
And Perseverance’s spying is far from over. While its primary mission will last a little over two years, it could remain functional for much longer—the Curiosity rover is still nine years into a projected two-year term.