(ORDO NEWS) — The findings suggest that trying to speak in the Martian atmosphere can have a strange effect, as higher sounds travel faster than bass notes. Not that we’re trying, since Mars‘ atmosphere is unbreathable, but it’s certainly fun to think about!
Scientifically, the results, announced at the 53rd Lunar and Planetary Science Conference by planetary scientist Baptiste Chide of Los Alamos National Laboratory, show high temperature fluctuations on the surface of Mars , which require further study.
The speed of sound is not a universal constant. It can vary depending on the density and temperature of the medium through which it passes; the denser the medium, the faster the sound travels.
This is why sound travels at about 343 meters per second in our atmosphere at 20 degrees Celsius, as well as 1480 meters per second in water and 5100 meters per second in steel.
The atmosphere of Mars is much thinner than Earth‘s, about 0.020 kg/m3 compared to about 1.2 kg/m3 for Earth. This alone means that sound on the red planet will propagate differently.
But a layer of atmosphere just above the surface, known as the planetary boundary layer, has added complications: During the day, surface heating creates convective updrafts that create intense turbulence.
Conventional instruments for measuring surface temperature gradients are highly accurate but can suffer from various interference effects. Luckily, Perseverance has something unique: microphones that let us hear the sounds of Mars, and a laser that can fire perfectly timed noise.
The SuperCam microphone was turned on to record acoustic pressure fluctuations from the rover’s laser breakdown spectroscopy instrument as it removes rock and soil samples on the Martian surface.
The results support predictions made using what we know about the Martian atmosphere, confirming that sounds propagate through the atmosphere near the surface at about 240 meters per second.
However, the quirk of the changing soundscape of Mars is something completely unexpected, and the conditions on Mars lead to a quirk not seen anywhere else.
At frequencies above 240 Hz, collision-activated vibrational modes of carbon dioxide molecules do not have time to return to their original state. As a result, sound travels more than 10 meters per second faster at higher frequencies than at lower frequencies.
This could lead to what the researchers call “unique listening” on Mars, where higher sounds reach the listener before lower ones.
Given that any human astronauts going to Mars soon will have to wear pressurized space suits with communications equipment or live in pressurized habitation modules, this is unlikely to pose an immediate problem, but it could be a fun concept for science fiction writers.
Since the speed of sound changes due to temperature fluctuations, the team was also able to use the microphone to measure large and rapid temperature changes on the Martian surface that other sensors could not detect. This data could help fill in some of the gaps in Mars’ rapidly changing planetary boundary layer.
The team plans to continue using the SuperCam microphone data to observe how things like daily and seasonal changes can affect the speed of sound on Mars. They also plan to compare acoustic temperature readings with readings from other instruments to try and figure out large fluctuations.
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