Microphone in the universe: Why do scientists want to listen to the sounds of alien worlds?

NASA's Perseverance rover, currently working on Mars, carries a microphone on its SuperCam.

(Image source: NASA/JPL-Caltech/Malin Space Science System)

Perseverance's microphones have proven to be invaluable to scientists and engineers, as they can detect winds on Mars and even hear the intermittent crackles of lasers inside the rover.

Similarly, the sound of the spinning propellers of the Ingenuity Mars helicopter and the pumps of the Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) aboard Perseverance were picked up by the microphone.

The instruments on board Perseverance in Jezero Crater have collected a wealth of valuable data, suggesting it's time to put microphones on probes heading to other planets.

International efforts

Timothy Leighton, a professor of ultrasonics and underwater acoustics at the University of Southampton in the United Kingdom, is a big supporter of countries installing microphones on probes to Mars or other planets.

"This work is more than just listening to the sounds," Leighton told space.com, because the data can tell researchers everything from winds, temperature, atmospheric chemistry and turbulence on Mars. "You can interpret a lot of information from the sounds," Leighton said.

Leiden is working to raise public interest in the sounds of other planets to ensure that policymakers send microphones to other planets.

Software Issues

Inside the Perseverance rover, the Mars Oxygen In-Situ Resource Utilization Experiment is wrapped in gold metal, and the sound it makes is detected by the microphone onboard the SuperCam. (Image source: NASA/JPL-Caltech)

To that end, Leighton donated a sound simulation kit to a local planetarium, with the goal of engaging with children and sparking their interest in science and engineering. The software in the kit simulates sounds produced in nature, such as thunder, wind and volcanic eruptions - these sounds accompany videos of the planetarium showing explorations of Venus, Mars and Saturn's largest moon Titan. The software can also change the voices of speakers or audience members to simulate how they would sound on other planets.

"It also provides a scientific basis for the sound," Layton said. "But the big breakthroughs came from Perseverance, and my work is tiny compared to that. It just gets people interested."

Audible sound

After landing on Mars in February 2021, NASA's Perseverance rover is the first to transmit audible sound data from the red planet.

The wheeled robot is equipped with two microphones: the SuperCam microphone, which is located on top of the rover's rotating mast, and another microphone on the stationary side of the rover.

The SuperCam microphone has recorded the sounds of wind and turbulence, as well as the sounds produced by the various instruments on the rover, which means we can also do a cheap, on-site analysis of how sound waves manifest themselves in Mars' thin, carbon dioxide-dominated atmosphere.

Sound Signature

The sounds recorded on Mars are generally produced by three reasons: atmospheric activity (such as wind and turbulence), shock waves generated by the Laser Induced Breakdown Spectroscopy (LIBS) instrument located on SuperCam, and sounds generated by the rover's own equipment, such as the sound of the motor turning the wheels.

For example, nearly every recording made by MOXIE's SuperCam microphone can be heard, according to Michael Hecht of MIT's Haystack Observatory.

"The reason this microphone is so high up on the rover is to minimize the chances that other equipment will interfere with its recordings," Hecht told space.com.

Another man-made sound is the spinning propellers of the Ingenuity Mars helicopter, which was close enough to the microphones on several test flights to be recorded.

Perseverance Playlist

"We now have a Perseverance playlist that contains hours of Martian sounds," said researchers Ralph Lorenz of the Johns Hopkins University Applied Physics Laboratory and Baptiste Kidder of the Space and Planetary Exploration Group at Los Alamos National Laboratory.

The most prominent of the Martian sounds, researchers reported at a recent meeting of the Acoustical Society, are the propellers of the Ingenuity Mars helicopter.

In a related paper, Lorenz said that collecting data from the helicopter is important for understanding the Martian atmosphere. In addition, these sound measurements are an important tool for us to diagnose the flight status of the helicopter, which may be important for future Mars sampling missions.

Lorenz and his colleagues also note that NASA's Dragonfly mission to Titan could also carry one or more microphones that could measure the operation of rotors or motors, perhaps picking up Titan's various sounds.

The test flight of the Ingenuity Mars helicopter was detected by Perseverance's microphone, which can provide invaluable engineering and science data. (Image credit: Ralph Lorenz et al. (NASA/JPL-Caltech, University of Arizona/HiRISE)

Signs of stress

Jupiter's icy moon Europa is thought by scientists to be a silent moon filled with active cryovolcanoes. (Image credit: NASA/JPL-Caltech/SwRI/MSSS; Image processing: Kevin M. Gill CC BY 3.0)

To plan future missions to other celestial bodies that will also carry acoustic equipment such as microphones and design them correctly, Leighton said it would be useful to predict the acoustic signatures produced on those worlds. These predictions could indicate whether a single-microphone system should be changed to a three-microphone system, he said.

Lightning on Venus is thought to occur about half as often as on Earth. It's also possible that lightning produces acoustic signatures, and dust storms on Mars can produce pressure signatures, Leighton said.

Then there is evidence for possible cryovolcanoes on Triton, Io and Europa, as well as Enceladus and Titan, Layton noted.

Final word: It turns out that outer space is also a great place for sound to travel.

BY: Leonard David

FY: Chen Li

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