by Katherine J. Wu
In space, no one would hear you scream.
But make a quick detour down to the surface of Venus, and all bets are off. Because even if you scream on another planet with no one else around to hear it, you’ll certainly make a sound – just not quite the one you’d make on Earth.
And with that cliffhanger, let’s tap the brakes for a second. What is sound, anyway? Without going too far down the rabbit (ear)hole, sound is a wave that carries energy. For this to happen, sound needs a medium like air, which contains molecules that can move and conduct the wave onwards. When sound hits a physical structure, like an eardrum, the structure vibrates. These vibrations are then conducted along a series of small structures in the middle and inner ear, creating mechanical disruptions that ultimately activate nerves that signal to the brain. Thus, there are several factors that determine how sounds are heard; the most important one we’ll cover today is the medium through which the sound travels. Outer space is mostly (but not entirely!) quiet due to the lack of air. But most planets in our solar system are surrounded by an atmosphere – an envelope of gases that is held close to the surface of the planet by gravity, allowing sound waves safe and efficient passage. In other words, a noisy, gassy embrace.
Although we have yet to record sound on the surface of another planet, we can make fairly confident predictions of what your voice would sound like by comparing what we know about atmospheric science and the differences between the environment here on Earth and on other planets. With Earth as a baseline, we can then mathematically model how sound waves would hit our ears after traveling through a different sort of atmosphere. In short, these estimations are akin to experimenting with warping your voice by speaking underwater or through a pillow: when an environment changes, so does the sound that is conducted through it.
In 2012, a team of researchers at led by Tim Leighton at Southampton University modeled what certain musical instruments would sound like on Venus, Mars, and Titan, Saturn’s largest moon. But we can extrapolate a bit from this and make some predictions about human voices as well. Notably, in these simulations, the researchers picked only a couple planets and moons to study. Mercury, for instance, was left out because it doesn’t have a real atmosphere due to its low surface gravity and proximity to tumultuous solar weather. Without an atmosphere, sounds are all but absent.
But when we do have an atmosphere to work with, there are several factors to consider. How much pressure is in the atmosphere? How humid is it? What’s the temperature? What gases are in the air? All of these affect air density, which will determine three things: 1) how our vocal cords vibrate, and thus the pitch we produce; 2) how quickly sound waves travel through the air, which affects acoustics; and 3) how efficiently sound waves travel through the air, which will change volume.
Table 1: Your voice on other planets (or moons), compared to here on Earth
|Titan||Slightly more bass||Slightly huskier||Louder|
So first, we have Venus. With the planet’s proximity to the sun, Venus’ atmosphere is like chowder – hot, soupy, and thick, with pressures similar to those found 3000 feet beneath the surface of the sea. The high air density would make our vocal cords vibrate slower, lowering the pitch of sound. Basically, we’d all speak basso profundo. On the other hand, because sound travels faster through liquid than air, Venus’ goopy atmosphere would conduct sound faster than Earth’s. The vocal tract would thus resonate at a higher frequency, making voices a bit squeakier. On Venus, we’d sound like Donald Duck. What’s more, Venus’ atmosphere has a great deal more carbon dioxide compared to Earth’s, which is primarily nitrogen. Carbon dioxide absorbs sound more than nitrogen does, which would somewhat muffle sounds and make them sound small or further away. All that said, this is really a moot point. We wouldn’t be able to breathe, let alone speak, without some pretty serious headgear in Venus’ actual atmosphere, which is not your grandma’s chowder – unless your grandma’s chowder is brutally hot, lung-crushingly heavy, and overall murderously inhospitable to human existence.
What about Mars, one of the most promising extraterrestrial locales for future human colonization? The atmosphere of Mars isn’t particularly friendly either – it’s also full of sound-sapping carbon dioxide, frigidly cold, and over a hundred times thinner than Earth’s atmosphere. This combination is the opposite of the hot, thick air on Venus, and our voices would have a lower pitch due to the icy temperatures and huskier from the slower speed of sound… that is, if we could hear them at all. On Mars, sound would travel at a lower speed through much more absorptive gas. You could be standing thirty feet from a shrieking banshee and hear next to nothing. It’d be a good place to open a Howler.
Last but not least, Titan. Despite being the most far-flung of our candidates – and not even a planet – Titan has always had a reputation of being Earth-like, with a nitrogenous atmosphere and organic molecules similar to those found on our home planet. The main difference is Titan is absurdly cold, and the sun would need to become a red giant to increase its temperature enough to warm Titan’s surface to habitability. But let’s put a pin in that for now. Given its other similarities to Earth, it may not be surprising that sounds on Titan would be mostly familiar, with two mild differences. First, while Titan is small, its icy temperature creates an atmospheric pressure about 50% higher than that on Earth; what’s more, sound travels slower in this atmosphere. Both these elements would give your voice a somewhat deeper pitch and a bit of that Macy Gray rasp. Second, despite the slower speed of sound, Titan’s atmosphere has more nitrogen than Earth’s, which means reduced sound wave absorption and slightly increased perceived volume. Listen to this sound bite, repeated thrice through different filters: Earth, Titan, and Venus.
And at long last, we can bring it all together in a grand finale: a comparison of sounds on Earth, Venus, Mars, and Titan. For that, check out these simulations of a snippet of Bach’s Toccata and Fugue in D Minor, adjusted to be, well, actually audible. After all, a mathematically modeled simulation of an organ masterpiece on different planets is worth a thousand words.
P.S. Some of you may be wondering if your galactic coordinates would change your likelihood of hearing “Laurel” or “Yanny.” The answer is… um, maybe. It’s complicated. The whole line of contention regarding Laurel vs. Yanny has to do with how each individual brain interprets noise from an imperfect recording – perception, rather than production, of sound. And the differences in sound perception on each celestial body take a backseat to the differences in sound production due to the major differences in atmosphere. That being said, The New York Times and other outlets have been able to sort of hack the Laurel-Yanny spectrum by changing the original recording to filter out certain frequencies – that is, altering things on the production side to bypass differences in perception. So I suspect that, for instance, if we were to produce the same ambiguous piece of Laurel-Yanny audio, an individual’s perception might be slightly more likely to hear “Laurel” on Venus and “Yanny” on Mars and Titan. If you want to know a little more about the original phenomenon, you can read about it here – without even leaving your home planet, and without me getting my foot in my mouth. Just don’t accuse me of resting on my yannys.
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Katherine Wu is a graduate student at Harvard University and Co-Director Emeritus of Science in the News. Special thanks to SITN’s Dana Boebinger, Stephen Portillo, and Kevin Sitek for major assists with scary things like planetary science, acoustics, and basically all of physics ever.
Header image by Andrew Caw.