Footage from NASA's Perseverance rover has added a new element to the knowledge that humanity has gleaned about Mars; while we have for many years grown to know how Mars looks, we now know its sounds.
Equipped with two microphones, the Perseverance rover has given NASA some five hours of audio recordings detailing the sounds heard on the Red Planet and som are publicly available.
“It’s like you’re really standing there,” Baptiste Chide, a planetary scientist who studies data from the microphones at L’Institut de Recherche en Astrophysique et Planétologie in France, said in a statement. “Martian sounds have strong bass vibrations, so when you put on headphones, you can really feel it. I think microphones will be an important asset to future Mars and solar system science.”
Perseverance is the latest of many probes and rovers sent to explore Mars, but it is the first to record sound. The microphones used are both off-the-shelf devices and are commercially available. One sits on the rover's mast and the other on its chassis.
However, the Red Planet is, as far as we know, uninhabited, and its atmosphere is very thin. As such, the recordings, upon first glance, would seem rather dull. Sounds of Perseverance rolling over gravel, its own lasers being sent from its SuperCam, the flight of the Ingenuity Mars Helicopter and the occasional gust of wind make up the majority of the recorded sounds.
But for scientists, the information gained from these audio recordings contains a wealth of data about the planet and its atmosphere. This is because sound itself must travel through vibrations in the air. Due to the Martian atmosphere being 100 times less dense than that of Earth's, scientists weren't even completely certain that their microphones would pick up any sound at all. And they hadn't picked up any until April 30, during Ingenuity's fourth flight.
The lasers from the SuperCam and resulting vapor further add to this data by ensuring that audible sound can be made.
This is done thanks to the Mars Environmental Dynamics Analyzer (MEDA), which NASA uses to study the Martian environment and atmosphere, with the rover's wind sensors and SuperCam helping study microturbulance, minute shifts in the air.
“It’s kind of like comparing a magnifying glass to a microscope with 100 times magnification,” said MEDA’s principal investigator, Jose Rodriguez-Manfredi of the Centro de Astrobiología (CAB) at the Instituto Nacional de Tecnica Aeroespacial in Madrid. “From the weather scientist’s point of view, each perspective – detail and context – complements one another.”
Already, scientists have made progress in understanding the Martian atmosphere and how it conducts sound, and it wasn't what was expected.Back in 2020, NASA had theorized that sounds emitted in the cold Martian atmosphere would take slightly longer to reach the ear from its point of origin. With an average surface temperature around -81 degrees Fahrenheit (-63 degrees Celscius), the speed of sound on Mars (around 540 mph, or approximately 240 meters per second) is lower than on Earth where it is around 760 mph, or 340 meters per second. This change would likely go unnoticed up close, but could be noticeable at a distance. Further, the fact that Mars's atmosphere is 96% carbon dioxide, which would absorb high-pitched sounds and prevent them traveling far due to a process known as attenuation.But now scientists will have to reconsider and they have actually ruled out two of the three models developed to understand how sound propagates on the Red Planet.
“Sound on Mars carries much farther than we thought,” said Nina Lanza, a SuperCam scientist who works with the microphone data at LANL. “It shows you just how important it is to do field science.”
But there is another far more mundane benefit to having microphones on the Perseverance rover: Maintenence.
Using microphones, the engineers on the mission can study the rover's performance much in the same way as listening to a car engine. The data gathered from these recordings can hopefully be used to study the condition of the various components of the rover over time.
“We would love to listen to these sounds regularly,” said Vandi Verma, Perseverance’s chief engineer for robotic operations at JPL. “We routinely listen for changes in sound patterns on our test rover here on Earth, which can indicate there’s an issue that needs attention.”