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A microphone on NASA’s Perseverance rover has helped scientists measure variations in the speed of sound in the atmosphere on Mars.
Located on a SuperCam, mounted on the head of the rover’s mast, the mic was indispensable to new discoveries about the speed of sound on the red planet which has an extremely thin atmosphere, mostly made of carbon dioxide.
Scientists found that the speed of sound on Mars varies with pitch (or frequency). On Earth, sounds typically travels at 767 mph (343 metres per second). But on Mars, low-pitched sounds travel at about 537mph (240 metres per second) while higher-pitched sounds move at 559 mph (250 meters per second).
Prior to the mission, scientists expected that the atmosphere on Mars would influence the speed of sound but had never observed the phenomenon until the recordings were made.
Another effect of the thin atmosphere that was uncovered was that sounds only carry a short distance on Mars and higher-pitched tones hardly carry at all. On Earth, sound might drop off after about 213 feet (65 metres). But on Mars, sound falters at just 26 feet (8 metres) with high-pitched sound lost completely at that distance.
The findings appear in an article published on 1 April in the Nature journal. Referring to sound capture on Mars, Sylvestre Maurice, an astrophysicist at the University of Toulouse in France and lead author of the study, said: “It’s a new sense of investigation we’ve never used before on Mars. I expect many discoveries to come, using the atmosphere as a source of sound and the medium of propagation.”
Scientists founds that Mars is largely a quiet planet, thanks to its low atmospheric pressure, but this atmospheric pressure varies with the season. “At some point, we thought the microphone was broken, it was so quiet,” said Sylvestre.
The mic also picked up sounds from the mission itself, such as the sound of spinning double rotors on the mission’s Mars helicopters which produced a distinctive, low-pitched sound at 84 hertz. A second mic, mounted on the chassis of the rover, was use to record the sound of the SuperCam’s own laser whose sparks generated a high-pitched noise above 2 kilohertz when vaporising rock.
Meanwhile, the SuperCam’s microphone has drawn praise.
“The microphone is now used several times a day and performs extremely well; its overall performance is better than what we had modelled and even tested in a Mars-like environment on Earth,” said David Mimoun, professor at the Institut Supérieur de l’Aéronautique et de l’Espace (ISAE-SUPAERO) and lead researcher on the team that developed the microphone experiment. “We could even record the humming of the Mars helicopter at long distance.”
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