Article published courtesy of NASA:
A new study based on recordings made by the rover reveals that the speed of sound is slower on the red planet than on Earth and that, most of the time, a deep silence reigns.
Listen carefully to the sounds of Mars, recorded by NASA’s Perseverance: the rover’s mechanical whine and click in a light Martian wind; the roar of the rotors on Ingenuity, the Mars helicopter; the crackling blast of a laser zapping rock.
This is exactly what an international team of scientists did by carrying out the first analysis of the acoustics of the red planet. Their new study reveals how fast sound travels through the extremely thin atmosphere, mostly carbon dioxide, how Mars might sound to human ears and how scientists can use audio recordings to probe subtle changes in atmospheric pressure on Earth. another world – and to assess the health of the rover.
“It’s a new sense of investigation that we’ve never used before on Mars,” said Sylvestre Maurice, an astrophysicist at the University of Toulouse in France and lead author of the study. “I expect many discoveries to come, using the atmosphere as a source of sound and a means of propagation.”
Most of the sounds in the study, published April 1 in the journal Nature, were recorded using Perseverance’s SuperCam microphone, mounted on the rover’s masthead. The study also refers to sounds recorded by another microphone mounted on the rover’s chassis. This second microphone recently recorded the puffs and pings of the rover’s Gaseous Dust Removal Tool, or gDRT, which blows shavings onto the rocks the rover has scraped to examine them.
The result of the recordings: a new understanding of the strange characteristics of the Martian atmosphere, where the speed of sound is slower than on Earth – and varies with pitch (or frequency). On Earth, sound typically travels at 767 mph (343 meters per second). But on Mars, lower sounds travel at around 537 mph (240 meters per second), while higher-pitched sounds travel at 559 mph (250 meters per second).
The varying sound velocities on the Red Planet are an effect of the thin, cold carbon dioxide atmosphere. Prior to the mission, scientists expected the atmosphere of Mars to influence the speed of sound, but the phenomenon had never been observed before these recordings were made. Another effect of this tenuous atmosphere: sounds only carry a short distance, and higher-pitched sounds hardly carry at all. On Earth, sound can drop off after about 213 feet (65 meters); on Mars, it fades out at just 26 feet (8 meters), high-pitched sounds being completely lost at that distance.
Recordings from SuperCam’s microphone also reveal previously unobserved pressure variations produced by turbulence in the Martian atmosphere as its energy changes on tiny scales. Gusts of Martian winds on very short timescales were also measured for the first time.
Hear what familiar sounds from Earth would sound like on Mars
One of the most striking features of sound recordings, Maurice said, is the silence that seems to reign on Mars. “At one point we thought the microphone was broken, it was so quiet,” he added.
This too is a consequence of Mars having such a thin atmosphere.
“Mars is very quiet due to low atmospheric pressure,” said Baptiste Chide of Los Alamos National Laboratory in New Mexico, also a co-author of the study. “But the pressure changes with the seasons on Mars.”
This means that, in the coming Martian autumn months, Mars could get noisier – and provide even more information about its otherworldly air and weather.
“We are entering a high pressure season,” Chide said. “Perhaps the acoustic environment on Mars will be less quiet than it was when we landed.”
This illustration shows the location of Perseverance’s two microphones. The microphone on the mast is part of the SuperCam scientific instrument. The microphone on the side of the rover was intended to pick up entry, descent and landing sounds for audience engagement.
The acoustics team also studied what the SuperCam microphone picked up from the spinning twin rotors of Ingenuity, the Mars helicopter that is the rover’s travel companion and aerial scout. Spinning at 2,500 rpm, the rotors produce “a distinctive, low-pitched sound at 84 hertz,” Maurice said, referring to the standard acoustic measurement of vibrations per second and the rotational speed of the two rotors.
In contrast, when SuperCam’s laser, which vaporizes chunks of rock from a distance to study their composition, hits a target, it produces sparks that create a high-pitched noise above 2 kilohertz.
Studying the sounds recorded by the rover’s microphones not only reveals details of the Martian atmosphere, but also helps scientists and engineers assess the health and functioning of the rover’s many systems, just as one might notice a noise disturbing when driving a car.
Meanwhile, the study’s key instrument, SuperCam’s microphone, continues to exceed expectations.
“The microphone is now used several times a day and works extremely well; its overall performance is better than what we had modeled and even tested in a Mars-like environment on Earth,” says David Mimoun, professor at the Institut Supérieur de l’Aéronautique et de l’Espace (ISAE-SUPAERO) and responsible from the team that developed the microphone experience. “We could even record the Mars helicopter hum from a long distance.”
Learn more about the mission
A key focus of Perseverance’s mission to Mars is astrobiology, including searching for signs of ancient microbial life. The rover will characterize the planet’s past geology and climate, pave the way for human exploration of the Red Planet, and be the first mission to collect and cache Martian rock and regolith (broken rock and dust).
Subsequent NASA missions, in cooperation with the ESA (European Space Agency), would send spacecraft to Mars to collect these sealed samples from the surface and return them to Earth for further analysis.
The Mars 2020 Perseverance mission is part of NASA’s Moon to Mars exploration approach, which includes Artemis missions to the Moon that will help prepare for human exploration of the Red Planet.
Jet Propulsion Laboratory, which is operated for NASA by Caltech in Pasadena, California, built and manages operations of the Perseverance rover.
To learn more about perseverance: