Challenger rocket taking off

The Science of Sound: Out-of-this-World Audio

Joseph Robinson

Feb 20, 2021
4
Minutes

On February 18th, the Perseverance rover joined its predecessors, the Curiosity rover and the Insight lander, by landing on the surface of Mars. Building off of trial and error, experimentation and innovation, Perseverance has been turning heads due to a capability its predecessors did not possess; Perseverance can record sound and transmit the audio back to us, a scientific achievement no other “Martian robot” was built to accomplish. The microphone onboard the Perseverance is a DPA 4006, an omnidirectional microphone which, according to NASA Jet Propulsion Laboratories’ David Gruel, “You could buy the exact same microphone, exact same components, off of the internet,” which is true. However, the price tag might be somewhat prohibitive to the average amateur recording enthusiast, coming in at $2400 MSRP. He continues, “Our hope is that our off-the-shelf microphone will help us learn something new about Mars that we wouldn’t know otherwise."

Changing Sound Waves

Sound on Earth moves at a speed of about 343 meters per second (767 mph); this however assumes dry air and a temperature of 20 degrees Celsius (68 F). On Mars, the average air temperature is -63 degrees Celsius (-81 F), which combined with the lower density of the planet’s atmosphere, causes sound waves to travel slower than on Earth. On the red planet, sound travels at an average of 240 meters per second (537 mph), losing about 33% of its speed.  In addition, the composition of the Martian atmosphere is almost entirely carbon dioxide, which will likely lead to lower-pitched sounds carrying more efficiently through the planet’s air. Basically, sounds on Mars will come across a little softer and perhaps “muffled” compared to the same sounds on Earth.

Theory and Reality

NASA has curated a playlist for those with curious ears, including an episode dedicated to Sounds of Mars, with some everyday audio manipulated to carry like it might on the surface of Mars. In the same list, you can find the first recorded sounds transmitted from Perseverance to Earth, catching some calm wind movement across the surface of the microphone. One recording includes a lot of high-pitched background hum from the rover, which tends to drown out the natural environment, due to the way sound travels through the structure of Perseverance itself.

https://soundcloud.com/nasa/sets/sounds-from-mars

Just like with sound theory, the mathematical applications involved in calculating landing vectors and accounting for planetary physics are ultimately all theories waiting to be put into practice. Once the lander collides with the Martian atmosphere, theory has a brush with reality, and the team has to deal with what they call “Seven minutes of terror,” while Perseverance passes through the atmosphere and loses radio contact with NASA due to extreme turbulence.

Stay for the Fireworks

Later, as the main mission of Perseverance continues, the rover will collect mineral samples and—using a highly sophisticated laser, a camera, and a second onboard microphone—blow some stuff up. The ways minerals react to heat and pressure is important, so they’ll be zapping some rocks which will burn, crack, and explode, and every bit of it will be recorded and transmitted back. As this technology improves, and while we continue sending unmanned missions to the red planet, we can look forward to more opportunities to come to understand our planetary neighbor, not just through images but through audio of such a quality that you feel like you might be surrounded by the winds of another world.  There will be some interesting audio coming from beyond our planet in the coming months and years, so while you surf channels and binge through your streaming catalogues, don’t forget to check in with Perseverance on Mars for a soundscape that is truly out of this world.

Explore more.