Physics

# Is the Speed of Sound the Same on Mars as on Earth?

The speed of light in a vacuum is the same anywhere you measure it in the universe, according to Einstein’s special theory of relativity. Whether you’re on Earth, Mars, or Zoozve, measuring the speed of light yields a chilly 299,792,458 meters per second (983,571,056.43 feet per second), the universe’s absolute limit.

Sound and light are not the same. Alien’s billboard explains that no one can hear you scream in space. Sound cannot travel through a vacuum because it is a vibration propagating as an acoustic wave through a material, whether liquid, solid, or gas.

Sound travels at varying speeds via such mediums, moving quicker through denser ones. Sound travels at a rate of 1,500 meters (5,000 feet) per second in water and approximately 340 meters (1,115 feet) per second in air. Sound travels more quickly in solids, however, the speed varies depending on the material. Scientists who attempted to calculate the quickest speed that sound could theoretically travel discovered that it decreases with atom mass, meaning that sound would be fastest if propagated through solid hydrogen.

Though solid hydrogen only forms at extremely high pressures, such as those found inside gas giants like Jupiter, they determined that sound would travel at 36 kilometers per second (22 miles per second) in it, which is most likely the greatest potential speed for sound.

This takes us to the answer to the question posed in the article title. Earth’s atmosphere is substantially thicker than Mars’, almost 100 times denser on our planet’s surface than on the red one. As a result, sound should travel slower there than it does here, assuming the atmosphere is thick enough to convey sound at any distance at all.

Of course, we have sound recordings from Mars, including one of a Martian dust devil, due to the army of robots we dispatched there. So we know that sound can go there experimentally.

Mars is one of just two planets where we have successfully measured the speed of sound. In a 2022 experiment, NASA’s Perseverance rover shot lasers at rocks and waited for its microphones to detect the resultant shockwave. The speed of sound fluctuates with temperature and altitude, much as it does on Earth, but the rover’s investigations revealed that the speed of sound in the Jezero Crater averaged roughly 240 meters per second (540 mph).

As day turns to night on Mars, the speed varies by about 10% due to the corresponding drop in temperature. However, sound on Mars remains strange.

Because of how sound travels through carbon dioxide at low pressure, the speed of sound in the audible bandwidth varies on Mars.

“For an acoustic wave with a frequency higher than ~240 Hz [just below middle C on a piano], CO2 vibrational modes activated through collisions do not have time to relax their energy,” the researchers wrote in their research article. “It turns out that on Mars, frequencies above 240 Hz travel at over 10 m/s faster than low frequencies. It may create a unique listening experience on Mars by introducing high-pitched sounds before bass.”

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