Scientists have confirmed the speed of sound on Mars, using equipment aboard the Perseverance rover to study the red planet’s atmosphere, which is very different from Earth’s.
The results suggest that trying to speak in the atmosphere of Mars may produce a strange effect, as high-pitched sound appears to travel faster than bass notes. Not that we’ll try, because the Martian atmosphere is not breathable, but it sure is fun to think about.
From a scientific perspective, the findings, announced at the 53rd Congress of Lunar and Planetary Sciences by planetary scientist Baptiste Chade of Los Alamos National Laboratory, reveal high temperature fluctuations on Mars that require further investigation. The speed of sound is not a universal constant. It can change, depending on the density and temperature of the medium through which it is transmitted; The denser the medium, the faster it is.
For this reason sound travels about 343 meters per second in the atmosphere at 20 degrees Celsius, but also at a speed of 1,480 meters per second in water, and 5100 meters per second in steel.
Also, the atmosphere of Mars is much weaker than that of the Earth. This alone means that the sound will propagate differently on the Red Planet.
But the layer of the atmosphere just above the surface, known as the planetary boundary layer, added complications: During the day, the rising surface temperature generates convective thrusts that create powerful turbulence.
Conventional instruments for testing surface thermal gradients are highly accurate, but may suffer from different interference effects. Fortunately, Perseverance has something unique: microphones that can let us hear the sounds of Mars, and lasers that can emit perfectly timed noises.
A SuperCam microphone is included to record acoustic pressure fluctuations from the rover’s laser-induced collapse spectroscopy as it removes rock and soil samples from the Martian surface.
The researchers measured the time between the laser firing and the sound reaching the SuperCam microphone at an altitude of 2.1 metres, to measure the speed of sound at the surface.
“The speed of sound recovered with this technique is calculated over the entire acoustic propagation path, which travels from the ground to the height of the microphone. Therefore, at any given wavelength, the skew is caused by changes in temperature, wind speed and direction along this path,” the researchers wrote in their paper. .
The results support predictions made using what we know about the Martian atmosphere, which confirms that sounds propagate through the atmosphere near the surface at a speed of approximately 240 meters per second.
However, the strangeness of the changing soundscape of Mars is something completely unfamiliar, with conditions on the surface of Mars leading to a strangeness not seen anywhere else.
At frequencies above 240 hertz, the collision-activated vibration patterns of the carbon dioxide molecules do not have enough time to relax or return to their original state. The result is that sound travels at more than 10 meters per second at higher frequencies than it does at lower frequencies.
This could lead to what researchers call a “unique listening experience” on Mars, where higher pitched sounds reach the listener faster than lower pitches.
Given that any human astronauts traveling to Mars anytime soon will need to wear pressurized spacesuits with communication equipment, or live in pressurized habitat units, this is unlikely to be an immediate problem — but it may be an interesting concept for science fiction writers.
Because 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 Mars that other sensors have not been able to detect. This data can help fill in some voids on the rapidly changing boundary layer of Mars.
The team plans to continue using the SuperCam microphone data to monitor how things like daily and seasonal changes affect the speed of sound on Mars. They also plan to compare the acoustic temperature readings with readings from other instruments to try to figure out large fluctuations.