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From Defacto Sound, you're listening to Twenty Thousand Hertz... The stories behind the world's most recognizable and interesting sounds. I'm Dallas Taylor. This is the story behind sound in our solar system.

[Star Trek SFX]

When you think about sound in space, classic films and television, like Star Trek, immediately come to mind.

[Star Trek theme]

From the ambient drones in Alien… [Alien drone SFX] to the galactic battle scenes in Star Wars… [Star Wars battle scene SFX] space truly is the final frontier in the study of sound.

Perhaps the best marketing tagline in movie history came from the Ridley Scott film, Alien: "In Space, no one can hear you scream." That phrase is true and not only because of the distance from Earth. It has to do with how sound travels.

Lori: I'm Dr. Lori Glaze. I'm the deputy director of the solar system exploration division at NASA's Goddard Space Flight Center.

Lori oversees about 300 scientists that study all the planets and small bodies of our solar system.

Lori: You don't have sound in space because sound requires molecules. You have to be able to move the molecules with the sound waves, and without the molecules there, the sound just doesn't move. You can try and use your lungs to push the sound out of your mouth but it won't travel anywhere.

That tagline from Alien I mentioned earlier, no one actually heard that either... as it was never read as voiceover in the trailer. It was just text, silent text, perhaps meant to imitate the specific science that explains how sound travels… or doesn’t.

Keith: My name is Keith Noll. I am the chief of the planetary systems lab at Goddard Space Flight Center. I think I've studied almost every planet or satellite in the solar system that has an atmosphere.

Keith knows his stuff about planets, and how sound might actually be possible on them.

Keith: What is sound? It's the vibrations of molecules in the air. It's a pressure wave [pressure wave SFX]. Of course sound can be transmitted through any kind of physical medium. If you are in a swimming pool [diving/swimming SFX] you can still hear sound. That's being transmitted through water. Earthquakes [earthquake SFX] are essentially sound waves being transmitted through the solid earth.

Sound takes on many forms but the kind we're most familiar with is pressure waves moving through gas.

The most common example of how different gasses affect your vocal cords is the old party trick of breathing in a helium balloon.

[balloon inflate SFX]

As the gasses, you're pushing it back out of your lungs over your vocal cords, [voice on helium example] because the density is lower, the vibration frequencies end up being higher and that's why you sound like Mickey Mouse.

Let’s go from planet to planet in our solar system, starting closest to the sun, what would it sound like on their surface to our ears?

Lori: Places like… Mercury and these rocky bodies with no atmospheres would be similar to being in space. There would not be much sound if any.

Keith: Mercury is an airless body, so we're back to listening for Mercury quakes [quake SFX], essentially. That would be really the only source of sound.

And you could only hear these Mercury quakes [quake SFX] if your head was pressed up against the rock, because there’s no atmosphere for sound to travel through.

Next up, Venus.

Lori: In my mind, what sound would be like on the surface, because you have this really dense atmosphere, much denser than Earth's, the sound would be more like or tend toward what things sound like when you're under water [underwater SFX].

If you could imagine something in between air and water, that kind of density, you're running your hand through that and you would feel that.

[continue underwater SFX]

If you were to just materialize on the surface in that environment of 900 degrees Fahrenheit and a hundred times our atmospheric pressure, you would first be crushed [crushing SFX] and then you would probably just burn up completely [burning SFX].

Keith: One thing we do know about Venus is that is has lightning, so you might hear thunder [thunder SFX].

I wonder what other things, like my voice, might sound like. [watery SFX on Dallas' voice] I’m on Venus in this ethereal world that’s a mix between a gas-like atmosphere and water. I’m almost floating, but yet it’s not as restrictive as being submerged in water.

My voice… The thunder… It’s all slightly muffled and distorted as it travels through the thick atmosphere.

[Earth SFX]

Now we’re home: Earth. We’re not going to stay here for long, but it’s worth mentioning the amazing diversity of sound on our planet. The sandy deserts… [sand and wind SFX] lush forests… [trees rustling and bird SFX] the sound of the ocean [ocean waves SFX], both on the surface… and below [underwater SFX]. It’s a rich soundscape, because our ears are perfectly in tune with it… More on that later.

Now Mars. And here’s where it gets interesting since Mars has been the subject of so much fascination for thousands of years. It’s one of the best places where life might have, or could exist.

Lori: Sound on Mars is going to be the opposite direction of Venus because the atmosphere on Mars is very, very thin compared to Earth's so there's just not very many molecules and sound requires molecules.

Countless movies have been made about Mars, including the Hollywood mega-hit The Martian, starring a stranded astronaut portrayed by Matt Damon.

Keith: Loved the movie. It was fun to watch, but it's not the Mars we know, it's a very different Mars.

[The Martian clip]

So the real Mars isn't anything like that, but Mars does have an atmosphere, albeit a thin one.

So that storm scene wasn’t quite accurate.

Keith: You wouldn’t necessarily hear the wind itself… You would hear the dust that's being picked up [dust SFX] and it would be banging against the faceplate of your spacesuit.

We also reached out to Scott Guzewich, a Research Astrophysicist at NASA.

Scott: So I enjoyed that movie a lot, but the atmosphere as it was shown was not scientifically right.

Basically, the problem with what you saw in the movie there where the atmosphere is so thick that it's picking up boulders and knocking things over [storm SFX]. It's just not possible. I mean the wind speed can get very high, as high as hurricane force at the surface sometimes.

So imagine a hundred mile per hour wind on Earth, if you're standing in a hurricane, obviously you'd be almost blown off your feet.

If you were standing on the surface there in Mars and you put your hand out in that hundred mile per hour wind, you would feel it, but it would feel like a gentle breeze [breeze SFX] here on the surface of Earth.

That sounds pretty cool. Standing in a hurricane but it only feels like a soft wind. But you’d die pretty quickly right?

Scott: You wouldn't die instantaneously but you'd want to be getting into shelter as fast as possible. First, the atmospheric pressure is dramatically lower than it is here on the surface of Earth. So, all the water in your body would attempt to boil, basically, instantaneously [water SFX]. The water covering your eye, the water in your mouth, and even the water in your cells and your blood. That wouldn't kill you right away but it would be very uncomfortable immediately. You could probably survive for a few tens of seconds, maybe a minute. You could potentially get a very rapid dose to frostbite on your entire body. Again, you wouldn't necessarily die right away, but it'd be quick.

And how about sound. What could we expect to hear?

Scott: Our ears aren't really designed to work in that sort of very near vacuum sort of atmosphere. So we wouldn't hear too much, maybe if you were scuffling along on the surface [gentle scuffling SFX], you could maybe very faintly hear that sound as you were clawing at the ground and gasping for air [gasping for air SFX].

The temperature obviously is colder in general, so that drives a slower speed of sound, and it seems that a lower speed of sound would tend to lower the pitch, [lowering pitch on Scott's voice] make your voice sound deeper… but then the atmospheric density would kind of go to raise your pitch [raising pitch on Scott's voice], so it seems like the pitch probably balances out.

If voices won’t carry far, how about a piano?

[piano music]

Scott: The very high-pitched, high frequency noise at the far right end of the piano, you probably wouldn't hear that at all, but maybe the deepest bass sounds that the piano makes, you might be able to just pick those up with a microphone if it was sensitive enough.

We’ve explored the first four planets of our solar system, and learned some of the ways their unique atmospheres and conditions shape their soundscape, or lack thereof. We’ll continue our exploration of sound to the outer reaches of our solar system, after the break.

[music out]

MIDROLL

[music in]

On to Jupiter, the King of Planets.

What’s interesting is that Jupiter doesn’t have a solid surface. Hard to imagine but the whole planet is made up of gas that just keeps getting denser and denser—eventually becoming a liquid the closer you get to its core. The pressure and temperature variations are what cause those beautiful swirling bands.

Keith: So the interesting thing on Jupiter is that the pressure and the temperatures where the cloud decks are, are actually not so inhospitable.

Cloud decks?

Keith: So you've got these very distinct cloud layers in Jupiter's atmosphere. So y’know, it's just fun to imagine. What would it sound like? Would you get these echos?... because you have these super powerful lightning bolts, more powerful than anything on the Earth, so you'd have really, really loud thunder [thunder SFX]. You'd hear echoes of echoes of echoes [thunder echoes] just back and forth. It's fun to think about.

How about the rest of the outer planets?

Keith: Jupiter and Saturn, I think you could consider to be pretty similar. Uranus and Neptune are pretty similar to each other. So all four atmospheres are primarily hydrogen and helium.

So if you tried to speak on any of them your voice would be higher?

Keith: I think so, cause the atmosphere is 75% hydrogen which is even less dense than helium and the rest is helium. I think we'd all be Mickey Mouse on Jupiter and Saturn.

And how about our old friend Pluto? Anything different?

Keith: It is probably the thinnest bound atmosphere that we know. But, it also looks really complex. It's got layers. It's pretty different. Mainly because the temperature is so low. Nitrogen there is an ice. Carbon monoxide is mostly an ice. That's probably the weirdest, most different kind of place in terms of thinking about how composition, temperature, pressure would affect the sound.

We’ve covered the planets and acknowledged our old friend Pluto, and it’s becoming clear that detecting sounds throughout our solar system is pretty difficult. So I’m curious, why is it so easy for us here on Earth?

Keith: Our ears are good for a very specific environment. They've evolved. Once you take them out of that they're probably not exactly the tool you would want. If you built an audio receiver and sent it to all these places… What could you hear that the human ear could hear, and more interestingly, what could you hear that the human ear would never be able to hear?

That's what I want to know.

Surprisingly, we have never recorded another planetary body with a traditional microphone.

So what does the future hold for us to truly be able to test our sound theories on other planets?

Scott: There is going to be a microphone on the next Mars Rover. The rover launched in 2020, it's supposed to have a microphone on it. We expect that it'll hear a few different things. The sound as the rover drives across the surface for example, will be transmitted both through the atmosphere and through the body of the rover itself. You should be able to hear the wheels kind of crunch along on the sand and on the rocks.

We’re so accustomed on Earth to hearing sound associated with what we see. But in true outer space no one can hear a titanic supernova explosion, or a hurtling asteroid smash into the moon, or even… hear you scream.

Lori: How rare is sound in the known universe? It's pretty rare. Even just in our known solar system, places like the moon and Mercury and these rocky bodies with no atmospheres would be similar to being in space. There would not be much sound, if any.

When we think of Earth as special in terms of being able to even support life, it goes much further than that. It’s one of the true places in the universe where sound is abundant and has impacted that life on an evolutionary level.

Scott: If you look at life on Earth, being able to hear something seems to be a very big advantage biologically. From very simple animal species [forest animal SFX], there is a benefit to being able to hear sound. Because you can become aware of either predators [growl SFX], or prey [squeal SFX], or food sources. So if I were to really get out my speculation hat, y’know alien life in the universe would probably have an advantage to hear things also... in whatever planet or ocean or atmosphere they lived in.

However, these aliens might perceive sound in a completely different way, a way that’s in tune with their own environment, and perhaps hear completely different frequencies.

When you think of space, it’s mostly… space. Where no medium exists to transport sound. Yet, it’s perfect for… light. Light fills the universe, but sound does not.

Keith: The whole universe is connected by light. Light anywhere in the universe can travel to anywhere else in the universe, but with sound you really are truly in different islands of sound and they're all isolated because they're all stuck in this space that doesn't transmit sound. It transmits light perfectly well but not sound.

Sound as we perceive and understand it, is so unbelievably rare, but it’s abundant right here, where we are, within this thin blanket of atmosphere. But if we travel straight up, it goes away very quickly. It gets quieter, and quieter… until it’s gone.

Twenty Thousand Hertz is presented by Defacto Sound, a sound design team dedicated to making television, film, and games sound insanely cool. Find out more at defactosound.com

This episode was produced and edited by Kevin Edds and me. With help from Sam Schneble. It was sound designed and mixed by Colin DeVarney.

We’d like to thank Dr. Lori Glaze, Dr. Keith Noll, and Dr. Scott Guzewich for speaking with us.

We’d also like to thank Elizabeth Zubritsky, Aries Keck, Nancy Jones, Richard Melnick, and Kevin Hartnett at NASA’s Goddard Space Flight Center.

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