Nearly two years after its launch, and almost 18 months after landing on Mars, NASA’s Perseverance rover has hours of audio recordings from the red planet’s atmosphere.
So, what does Mars sound like? On the whole, it’s quiet. Very quiet. But the recordings did pick up interesting weather events and changes which give us a better overall picture of Mars’s clime.
Perseverance’s primary mission is to explore sediments in a dormant river delta on the edge of the 45 kilometre-wide Jezero Crater, to learn about the crater’s formation and hopefully find signs of ancient life. But microphones are light and cheap, so it made sense to add a couple to the rover’s instruments.
The first audio from Mars was sent by Perseverance earlier this year. Now, a year’s worth of recording from the Martian atmosphere has been condensed into about five hours of sound.
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The findings are due to be presented by Baptiste Chide of the Los Alamos National Lab during a seminar, “Mars soundscape: Review of the first sounds recorded by the Perseverance microphones,” at the 182nd Meeting of the Acoustical Society of America tomorrow, May 25, in Denver in the US.
With no large dynamical natural phenomena, extant animal species (that we know of), industrial civilisation, or extreme weather events, you’d expect Mars to be pretty silent. And it is. Under the same conditions on Earth, sounds are 20 decibels louder than on Mars.
“It is so quiet that, at some point, we thought the microphone was broken!” says Chide.
But, like giving a new music album a second run-through, closer listening revealed some fascinating phenomena. The group heard much variability in the wind and abrupt changes in the atmosphere, see-sawing from calm to intense gusts.
The team noticed that the red planet’s soundscape is seasonal. During winter, carbon dioxide freezes in the polar caps. This causes changes in atmospheric density, and environmental volume fluctuates by about 20%. Atmospheric CO2 also causes high-pitched sounds in the distance to become fainter.
The rover also used laser sparks to calculate the speed of sound’s dispersion, confirming a theory that high-frequency sounds travel faster than low frequencies.
“Mars is the only place in the solar system where that happens in the audible bandwidth because of the unique properties of the carbon dioxide molecule that composes the atmosphere,” notes Chide. While the rover will continue to record audio as it travels across Mars’s surface, Chide believes that the technique could be applied to studies of other celestial bodies. Planets and moons with denser and more volatile atmospheres, such as Venus and Titan, may yield even more information as sound waves interact more strongly and travel further.
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