According to a new study based on rover recordings, the speed of sound on Mars is slower than on Earth, and there is a deep quiet most of the time.
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Listen carefully to the noises captured by NASA's Perseverance on Mars: the rover's mechanical whine and click in a mild Martian breeze; the spin of rotors on Ingenuity, the Mars helicopter; the crackling strike of a rock-zapping laser. A multinational group of scientists has done just that, conducting the first audio investigation on Mars. Their new research exposes how quickly sound travels through Mars' thin, largely carbon dioxide atmosphere, how Mars would sound to human ears, and how scientists can use audio recordings to examine minute air-pressure changes in another world — as well as the rover's health.
The study's principal author, Sylvestre Maurice, an astronomer at the University of Toulouse in France, stated, "It's a new sense of research we've never utilized before on Mars." "I anticipate a slew of new discoveries involving the use of the atmosphere as a sound source and transmission medium."
The majority of the sounds in the study, which was published in the journal Nature on April 1, were captured using the microphone on Perseverance's SuperCam, which is positioned atop the rover's masthead. The paper also mentions sounds captured by a microphone positioned on the rover's chassis. The rover's Gaseous Dust Removal Tool, or gDRT, which blows shavings off rocks that the rover has scraped in order to analyze, was recently recorded by this second microphone.
The recordings yielded a fresh knowledge of the peculiar properties of the Martian atmosphere, where sound travels at a slower speed than on Earth — and fluctuates with pitch (or frequency). On Earth, sound travels at an average speed of 767 miles per hour (343 meters per second). Low-pitched noises travel at 537 miles per hour (240 meters per second) on Mars, whereas higher-pitched sounds travel at 559 miles per hour (250 meters per second).
The planet's variable sound velocity is caused by its thin, cold carbon dioxide atmosphere. Prior to the journey, scientists expected that the atmosphere of Mars would impact sound speed, but the phenomenon had never been observed until these recordings. Sound travels only a short distance through the thin atmosphere, and higher-pitched tones travel even less. Sound fades after 213 feet (65 meters) on Earth, but only 26 feet (8 meters) on Mars, with high-pitched sounds being lost at that distance.
The recordings from SuperCam's microphone also indicate previously unseen pressure variations caused by turbulence in the Martian atmosphere as its energy varies on microscales. For the first time, Martian wind gusts on very short timescales were also measured.
Hear What Sounds Like on Earth Would Sound Like on Mars
The silence that seems to dominate on Mars, according to Maurice, is one of the most startling elements of the sound recordings. "We believed the microphone was damaged at one point since it was so quiet," he added.
Because Mars has such a thin atmosphere, this is also a result.
"The low air pressure on Mars makes it very silent," said Baptiste Chide of the Los Alamos National Laboratory in New Mexico, who was also a co-author of the paper. "However, on Mars, the pressure varies with the seasons."
That implies Mars may get noisier in the coming Martian fall months, providing even more insights into its alien air and weather.
"We're about to enter a high-pressure season," Chide explained. "Perhaps the aural environment on Mars will be noisier than when we first arrived."
The Mission's Sounds
The acoustic team also looked at what the SuperCam microphone picked up from the Ingenuity, the rover's traveling companion and aerial scout, spinning double rotors. The rotors emit a "distinctive, low-pitched sound at 84 hertz," according to Maurice, referring to the conventional acoustic measure of vibrations per second and the rotation rate for both rotors.
When SuperCam's laser, which vaporizes fragments of rock from afar to investigate their composition, hits a target, it produces sparks that produce a high-pitched noise above 2 kilohertz.
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