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In 1947, Chuck Yeager flew the X-1, an experimental rocket plane, over Rogers Dry Lake in Southern California and broke the sound barrier for the first time. To pull it off, he had to fly his plane at speeds exceeding 662 miles per hour, which is the speed of sound at an altitude of 25,000 feet. On the ground, where the atmosphere is denser, sound moves more quickly, at roughly 340 meters per second or roughly 760 miles per hour.
That relationship between atmospheric composition and traveling soundwaves becomes increasingly important on other planets with atmospheres drastically different from Earth’s. Now, for the first time, we’ve experimentally measured the speed of sound on Mars, and the results might surprise you.
A team of scientists used instruments on the Perseverance rover to capture and analyze sounds from the Martian wind, the Ingenuity helicopter in flight, as well as pumps and lasers present on the rover itself. The results were announced by NASA’s Jet Propulsion Laboratory and published in the journal Nature.
“Our microphone sits on top of a one-ton rover with a lot of instruments. We have the pumps that circulate fluid to warm the rover and we also have the SuperCam, which is a laser-based instrument that vaporizes rock and creates a plasm which generates a shockwave,” Baptiste Chide from the Space and Planetary Exploration Team at the Los Alamos National Laboratory told SYFY WIRE.
By analyzing the sound characteristics of a rock being vaporized, scientists can learn about the properties of the rock. That’s the central role of the microphone, but researchers turned the microphone on the larger Martian environment to analyze the way sound travels.
The atmosphere on Mars is exceedingly thin as compared to Earth, at less than one percent of Earth’s pressure. It’s also cold and made up of 95% carbon dioxide, both of which have strange effects on the way sound waves travel.
“Because of these different properties, sound doesn’t behave as it does on Earth. Sound speed on Mars is 240 meters per second and surprisingly we highlighted two different speeds of sound,” Chide said.
In the Martian atmosphere, sound speed is dependent on the frequency of the sound waves. High frequency sounds travel at about 10 meters per second faster than low frequencies waves, as a consequence of the low-pressure carbon dioxide atmosphere. In essence, had Chuck Yeager been flying on Mars, he might have had the opportunity to break the sound barrier twice, in sequence.
If and when humans ever colonize Mars, we’ll be living in pressurized environments closely matching the atmospheric conditions on Earth, so the impact of the Martian atmosphere on Mars should be negligible. However, these properties could have interesting consequences for any intelligent life which does pop up on planets with different atmospheric conditions. Music played on the surface of Mars would begin to sound distorted over relatively short distances, with the high-frequency portions of your favorite tunes reaching your ears before the lower ones. Moreover, it might be difficult to carry a conversation without the aid of electronic communications devices.
“On Mars, we have this huge attenuation with distance. Carbon dioxide is made of three atoms and vibrates in such a way that it absorbs high-frequency sound. If we had a conversation separated by 2 meters, it would be equivalent to 60 meters on Earth,” Chide said.
The study highlights the potential for future acoustic surveys of other solar system bodies. Chide specifically called out Saturn’s moon Titan, which has an atmosphere of comparable density to Earth’s made up of nitrogen and methane, both of which are good for sound conduction. Moreover, Titan has an active meteorological cycle with rivers, lakes, and rainfall made up of liquid ethane and methane.
Future probes to Titan could carry microphones to capture alien soundscapes, allowing humans of the future to fall asleep to the calm sounds of Titanic rainfall beneath a gently falling Saturnset. We have to admit, that sounds nice.