Although Earth and Mars are completely different planets, it is comforting to know that our voices sound very similar on both, but not the same. On the red planet would you hear a version quieter and muted. This is because on Mars, the atmosphere is completely different. But, the biggest change to the audio would be the high-pitched sounds, louder than most voices. Some sounds we are used to on Earth, such as whistles, bells, or birdsong, would be almost inaudible on Mars.
When we hear a sound, what we are really experiencing is our eardrums vibrating. That vibration comes from pressure waves traveling to our ears from the source of the sound. To reach our ears, the waves need a fluid to travel through, such as air. Sound waves can travel through liquids and even solids, but most of what we hear comes from the air. Our planetary neighbor, for example, has an unusual atmosphere compared to Earth, with vastly different temperatures, densities, and chemistry. This differences would completely change the sound we would hear.
As if this were not enough, the sound also informs us of characteristics of the environment, as it happens with echolocation that some animals like bats use to locate themselves. Thus, sound gives us complementary information to sight. So we may know what other planets look like, like the dusty rust-orange surface of Mars or the vibrant bluish-green of Uranus. But what do those planets sound like?
Timothy G. Leighton, of the University of Southampton in the UK, designed a software program that produces alien ambient sounds and predicts how human voices might change on distant worlds. And the has presented at the annual meeting of the Acoustical Society of America.
Acoustic studies became essential during the descent of the Huygens lander into Titan’s atmosphere in 2005 and on the more recent Mars InSight and Mars 2020 missions. These successful missions led to custom active and passive acoustic sensors that operated on a wide spectrum, from very low frequencies (infrasound, below the human hearing threshold) to ultrasound (above the human ear).
“For decades, we have sent cameras to other planets of our solar system and we have learned a lot from them. However, we never really heard what another planet sounded like until the very recent Mars Perseverance mission,” Leighton said.
Scientists can harness sound from other worlds to learn about properties that would otherwise require a lot of expensive equipment, such as the chemical composition of rocks, how atmospheric temperature changes, or the roughness of the ground. The alien sounds they could also be used in the search for life. At first glance, Jupiter’s moon Europa may seem like a hostile environment, but beneath its ice shell lies a potentially life-supporting ocean.
“The idea of sending a probe on a seven-year journey through space, then drilling into or melting the seabed poses mind-boggling challenges in terms of finances and technology,” Leighton adds. The ocean on Europa is 100 times deeper than Earth’s Arctic Ocean, and the ice sheet is about 1,000 times thicker. However, instead of sending a physical probe, we could let the sound waves travel to the bottom of the sea and come back and explore for us.” From now on, then, we will be all ears, aliens, but ears at last.