(ORDO NEWS) — Scientists have confirmed the speed of sound on Mars by using equipment from the Perseverance rover to study the red planet’s atmosphere, which is very different from Earth’s.
What they found could have some strange implications for communication between future Martians.
The results of the study show that trying to talk in the atmosphere of Mars can lead to a strange effect, as higher-pitched sound travels faster than bass notes. Not that we’re trying, since Mars’ atmosphere doesn’t breathe, but it’s certainly interesting to think about!
From a scientific standpoint, the results of the study, reported at the 53rd Lunar and Planetary Science Conference by Baptiste Schide of the Los Alamos National Laboratory, indicate high temperature fluctuations on the surface of Mars that 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 it passes.
This is why in our atmosphere at 20 degrees Celsius sound travels about 343 meters (1125 feet) per second, in water 1480 meters per second, in steel 5100 meters per second.
The atmosphere of Mars is much denser than Earth’s: about 0.020 kg/m3 compared to 1.2 kg/m3 on Earth. This alone means that sound will propagate differently on the red planet.
But the layer of atmosphere just above the surface, known as the planetary boundary layer, poses additional challenges: During the day, surface heating results in convective updrafts that create intense turbulence.
Conventional surface thermal gradient testers are highly accurate but can suffer from various interference effects. Luckily, Perseverance has something unique: microphones that let you hear the sounds of Mars, and a laser that can produce perfectly synchronized noise.
The SuperCam microphone was turned on to record acoustic pressure fluctuations from the rover’s laser breakdown spectroscopy instrument as it burns rock and soil samples on the Martian surface.
As it turned out, this brought great benefits. Chide and his team measured the time between the laser shot and the sound reaching the SuperCam microphone at a height of 2.1 meters to measure the speed of sound at the surface.
“The speed of sound obtained using this method is calculated over the entire acoustic propagation path, which runs from the ground to the height of the microphone,” the researchers wrote in their paper at the conference.
“Therefore, at any given wavelength, it is distorted by fluctuations in temperature, wind speed and direction along the way.”
The results confirm predictions made based on 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 quite unusual: conditions on Mars lead to a quirk not found anywhere else.
“Due to the unique low-pressure properties of carbon dioxide molecules, Mars is the only terrestrial planet atmosphere in the solar system to experience a change in the speed of sound right in the middle of the audible frequency range (20 Hertz to 20,000 Hertz),” the researchers write.
At frequencies above 240 Hertz, the collision-activated vibrational modes of carbon dioxide molecules do not have enough time to relax or return to their original state. As a result, sound at high frequencies travels more than 10 meters per second faster than at low frequencies.
This could lead to what the researchers call a “unique auditory experience” on Mars: higher-frequency sounds will reach the listener faster than lower-pitched ones.
Considering that soon astronauts going to Mars 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 an interesting 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 about 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 could affect the speed of sound on Mars. They also plan to compare acoustic temperature readings with readings from other instruments to try to find out the reasons for the large fluctuations.
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