NASA's Curious Universe - Hum of the Sun

Episode Date: November 14, 2023

What does space sound like? It’s a question that has fascinated composers and scientists alike throughout history. Through a process called data sonification, heliophysicists are using NASA satellites like audio recorders to listen to the electromagnetic symphony our Sun plays, and making new discoveries along the way. NASA's Curious Universe is an official NASA podcast. Discover more adventures with NASA astronauts, engineers, scientists, and other experts at nasa.gov/curiousuniverse

Hi, curious universe listeners. I have a question for you. What does space sound like? We'll see things like material from the surface of the sun that wants to extend outward into planetary space, but then it gets caught on a magnetic field line and pulled back down to the surface of the sun. Every now and then, these magnetic field lines will kind of get twisted up,

and they'll no longer be able to keep their hold to the surface. surface of the sun and they'll go flying out into space. And when this happens, when we get something like a coronal mass ejection, the amount of material that leaves the sun is oftentimes greater than the entire mass of the planet Earth. This is Robert Alexander. He's a data sonification specialist that studies the heliosphere, our sun's sphere of influence in space. Our nearest star is a dynamic and turbulent one.

Most scientists turn data about its explosive activity into charts and graphs. Traditionally, we would look at that, and it would be a line that would just kind of, whoop, it'd go up and come back down. Robert translates it into sound. Rather than just plotting it and looking at it, we can also listen to this eruption of particles, and when we listen to it, it sounds like an explosion. The first time I would play some of these sounds back for a research scientist, And something that had always been a line on the screen suddenly was filling the room with this explosive sound. There's this kind of emotional connection that you can form with it, and it sounds raw, and it sounds powerful in a way.

What you just heard there was a coronal mass ejection, exploding out from the sun and accelerating to more than a million miles per hour, before crashing into the Parker Solar Probe, then traveling 14 million miles and arriving at the Stereo A spacecraft. How wild is that? This is NASA's curious universe. Our universe is a wild and wonderful place. I'm your host, Patty Boyd, and in this podcast, NASA is your tour guide. If you could listen to a star, what would you hear? In this episode, learn how Robert and other NASA experts are doing just,

that, listening to our sun to learn its secrets through a process called data sonification. Heliophysicists are used to reading charts and looking at stunning images from spacecraft. But more recently, they've discovered that by closing your eyes and trusting your ears, you can discover things you never could have seen. Our specific community who study plasmas in your space environment, we actually started using sound back in the dawn of the space age. That's Mike Hartinger, a heliophysics research scientist at the Space Science Institute, and NASA collaborator. Before the first rockets left Earth's atmosphere, space scientists pointed radio antennae up to the sky, wondering what they might hear, trying to tune in to the vast universe above them.

Sometimes it was as simple as, you know, you have an antenna and you just listen to what's coming out of a speaker in real time. And, you know, you hear things like whistles. People coined the term whistle waves. You would hear this repeatable pattern, every dawn, that sounded kind of like a chorus, like a human chorus. And the term was actually coined dawn chorus. When NASA started launching satellites, scientists heard those waves again, this time from space. And so these terms were coined as people were listening to these things through speakers, just when we were starting to launch satellites.

And if you listen to these things, they're really like ethereal, they're really beautiful, and they just make you pause and think like, wow, that's happening right above my head. And there's this whole invisible world to us that you can kind of interact with with sound. But what exactly were those early scientists hearing? To understand the sounds of space, we have to start with the stars. Specifically, our closest star, the sun. So the sun is a giant ball of gas, really hot gas that we call a plasma. From here on Earth, the sun looks like a giant,

Yellow ball, stable and unchanging. But if you could get up close and zoom in... You know, of course you're going to see this giant yellow ball, but if you look at that yellow ball, even through a telescope, you'll see that there are these little dark spots, what we call sun spots, on the surface of the sun. And they're constantly changing, like on a timescale of days or weeks, you'll see them kind of pop up and go away,

and they'll move as the sun rotates from our point of view. Those dark regions, the sunspots, are actually cooler in temperature than the rest of the sun. But they're also the sun's most active regions, full of strong magnetic fields. You can also see these arcs of plasma shooting out from the sun. They look like little loops, and you see bubbling plasma coming up to the surface and bubbling up and going back down, kind of circulating. These sunspots are the launch pads for dramatic outbursts of radiation and plasma called solar. solar flares, and coronal mass ejections. When things on those active regions get too hectic,

big loops of plasma can stretch away from the sun and break loose from its magnetic fields flying off into space. So the sun is dynamic. It's constantly blasting out plasma at different speeds, and this plasma kind of just expands out away from the sun into what we call the solar wind. On Earth, we live in that solar wind, in the atmosphere of our sun.

We're constantly being hit by a blowing stream of particles, moving at a million miles an hour. Luckily, we have a shield here on Earth, one that protects us from the relentless solar wind and the sporadic explosions of radiation plasma that come our way from solar flares and coronal mass ejections. And that shield comes from deep within our planet. So the Earth has a magnetic field generated

in the core of the Earth, the liquid metal core, and basically from the circulation in that core, you get a magnetic field that kind of looks like a bar magnet. If your eyes could see magnetic fields, when you looked at a bar magnet, you'd see lines coming out of the top or north end and looping around to the bottom, or south end. Earth's magnetic field looks the same.

Those lines are just coming out of the south pole, looping out around through space, and going back into the North Pole. Earth's magnetic field is why compasses always point north. But it also has a more important role. It extends way out into space until it meets and matches the solar wind coming from the sun, pushing back against it like a cosmic arm wrestling match.

So you've got the solar wind, which has plasma and magnetic field in it, and it pushes against the Earth's magnetic field in plasma, and there's a balance that gets achieved. The region that's dominated by the Earth's magnetic field, we call it the magnetosphere. The magnetosphere is an action-packed space. It's constantly shifting and changing as its magnetic field lines are compressed by the force of the solar wind and explosions of plasma. I would say that the solar wind is always changing.

It's always kind of tickling the Earth's outer boundary in different ways, you know, vibrating it, tickling it just a little bit. but it's basically staying in that more or less that equilibrium. But then, yeah, when you have a solar wind with some kind of big structure like a coronal mass ejection, it's like a punch or a big push. That all means that what looks like empty space is actually a busy, bustling place full of activity. Space is not empty.

It's full of charged particles and magnetic fields that are plasma. If you look up in the night sky, you know, and you look out into the dark there, you know, as you get maybe 100 miles up in altitude, you start getting lots of this plasma. And it's constantly moving around. It's constantly vibrating. Different types of plasma are constantly interacting with each other. And so all these dynamics or all these behaviors create what I would call a soundscape. You may have heard that in space, no one can hear you scream.

That's definitely true. You know, if you went out into space and you were an astronaut and you took your space, home and off. That would be a terrible idea, but you also wouldn't hear anything. That's because here on Earth, what you hear is sound, city traffic, chirping birds, a plucked guitar string, are actually waves of air pressure vibrating your eardrums. Space doesn't have any air, and the pressure's way too low to hear sounds like we do here on Earth. So what Mike's saying about a soundscape in space might sound a bit wild. But in the sun's atmosphere of low-density plasma, other sorts of waves can travel.

Plasma waves with electric and magnetic fields we can detect. You definitely couldn't hear those plasma waves in the same way that you hear sounds on Earth. Your eardrum can't detect electric and magnetic fields. But these waves behave a lot like the sound waves we're familiar with. In fact, we mathematically we describe them, the same way we describe, very similar way we describe sound waves on the Earth's surface. You can think of the Earth's magnetic field,

those kind of magnetic field lines on a bar magnetic, If they are vibrate, they're kind of like vibrations on a guitar string. So they're a lot like sound waves. We just can't hear them with our eardrums. When those waves collide with Earth's magnetic field lines, they cause vibrations called resonances, just like a guitar string wiggling back and forth after you pluck it. When a NASA spacecraft flies through the same spot,

we collect a lot of data that scientists can print out on charts, squiggly lines representing those waves visually. But they can also play them aloud. It's a process called data sonification. That's where Robert Alexander comes in. So I take data from the sun in the heliosphere and turn it into sound. If we were to go into an old school recording studio, we would be recording on magnetic tape. So we've got the lead singer of the band.

They're laying down the vocals. We've got the bassist. We've got the drummer. We're recording all these instruments on magnetic tape. And then to play it back, we take those. magnetic recordings and then turn them into electrical signals and then use those electrical signals to move a speaker cone. To record earthly sounds, you use a microphone to turn pressure waves into magnetic and electric ones. To listen to space sounds, you can do the opposite. You convert electromagnetic waves to pressure waves we can hear.

Out there in space, all the time, we have satellites that are gathering magnetic measurements from the sun in the heliosphere. So I like to think of satellites as kind of like the most expensive, fancy recording studios that are floating out there in space. And just basking in all these rich data sets, gathering the greatest hits of the sun. And for me, I think of NASA's data archive, like an old, dusty record collection. Ten years ago, Robert teamed up with NASA's Goddard Space Flight Center and scientists at the University of Michigan to do just that. Dig into the data, pull out the records, and help scientists listen to the music of the sun. When I first started working with the solar heliospheric research group, I walked in the room and they would put plots up and they'd have these massive spikes in things like the velocity of the solar winds. And they would get so excited and so geeked at these plots.

But for me, I didn't have the same background that they had. So for me, sonification was a really helpful tool to be able to. to translate their enthusiasm from their domain into this more universal language that I was able to understand. Robert's a scientist, but he's also a composer. So he started by listening to the sun as an instrument and exploring it through music. In the sonification you're hearing, the wooching is generated by changes in the solar winds velocity, and the layers of voices represent changes in temperature. When it gets hotter, the voices get higher in pitch. And can you pick out the explosions?

When a coronal mass ejection or CME happens in the data, everything gets louder. That's a lot of information packed into music. And then the research team posed a challenge. They asked Robert if he could listen closely enough to the sun to discover something totally new. And in a moment of inspiration, I thought, what if I take these data streams and I write it directly to an audio file? And I remember I was sitting at a coffee shop the first time that I listened to. this. The sun is really turbulent. So to find order in the audio chaos, Robert first had to filter out some of the background noise. Once he did, he heard a pattern, a hum. And so I'm listening

to data, and I was sure that I had made some mistake in my calculations, because I kept hearing this noise in every one of my files. And I was like, oh man, I got the numbers wrong. I got to go back and do all this again. And as I continued listening, I thought to myself, what if this is actually a feature in the data rather than some kind of air in my calculation. And so I went back and I crunched some of the numbers and it turned out that the hum that I was hearing was exactly correlated with the solar rotational period, which is around 26.5 or 27 days. And so what I was hearing was the rotation of the sun. I remember I messaged my friend.

I had a little message window up and I was like, oh my gosh, I'm hearing the sun rotating. So there we're listening to 60 years worth of solar rotational data, and the rise and fall of that hum correlates with the rise and fall of solar activity with what's called the solar cycle. Right now, at the end of 2023, we're nearing the peak of the solar cycle, and seeing more and more sun spots, solar flares, and coronal mass ejections. In the data, Robert realized he could hear those features on the sun disappearing and reappearing as the sun rotated. When we have just one feature that rotates around on the sun,

we get the fundamental frequency, which is that 27-day rotational period. Then Robert started to hear something else, in addition to that fundamental frequency sound, as more sunspots and activity appeared, something that sounded a lot to the trained composer like music. I realized not only can I hear the rotation of the sun, but I can hear harmonics above this fundamental frequency.

Listen closely. Do you hear the solar winds music? When we get two regions that rotate together on opposite sides of the sun, we get an octave above that fundamental frequency. If we have three regions, they're now, if you kind of visualize it, they're equally spaced in thirds around the sun. And this creates an octave and a fifth. And above that, we get two octaves, and then we get the major third, and then the fifth. This creates these musical harmonic components in the solar wind. When you listen closely to the audio, you get this...

Above the... And then depending on how much of the turbulent noise you filter out, you can hear the... ...higher order harmonics. I go back and I take these results and I show them to the research group. And they're like, oh yeah, of course they're harmonics. It's a part of the way that the magnetic field superimposes itself over the sun and that heads out and into the solar wind.

And still just my mind was blown. It's like, you can hear the harmonic series in solar data. It's crazy. Robert had started out by trying to turn the sun's sounds into music. But it turns out the sun makes music of its own. And while listening to the sun's harmonics, turning the solar data into sound, Robert and his team made a new discovery about the solar wind

that scientists had never seen by simply looking at the data. By measuring the strength of these harmonics across elements like oxygen and carbon, they produced the most sensitive diagnostic of the electron temperature of the solar wind ever recorded. And there I got the rush, you know, the adrenaline rush of the realization that we can listen to sounds from the sun, and make new scientific discoveries that expand our understanding of the sun and of the heliosphere. Today, Robert's part of a new NASA citizen science project, alongside heliophysicist Mike Hartinger, trying to make new discoveries by listening to the sun.

It's called harp, short for heliophysics, audified, resonances in plasmas. So we love acronyms in heliophysics. Scientists just love acronyms, right? So, you know, our acronym is harp. And we're studying basically a massive magnetic harp in outer space where if you look at the Earth's magnetic field, you can kind of look at it from the perspective of a harp where the harp strings are short close to the earth

because the Earth's magnetic field lines are short. And if you move away from the Earth, these minuteic field lines or magnetic strings get longer and longer. And the analogy is really pretty exact because you definitely hear the pitches of these waves get lower and lower as you move away from the Earth. To study Earth's magnetic harp, the team is using data from a satellite called Themis. And lift off of a Delta 2 rocket carrying Themis.

NASA's revolutionary journey to study the northern lights. And it looks kind of like a box, and it's a box that's spinning. It's got all these sensors and it's measuring magnetic fields as it's going all the way around on its orbit. As the Thames satellite orbits Earth, it flies through the different strings of Earth's magnetic field, picking up the resonances the solar wind creates when it hits them and plays them, like plucking a harp string. To study a harp, you need to basically pluck all the different strings.

Luckily, Themis is set up to do that. It has an elliptical orbit, sort of like an oval-shaped path it takes around the Earth. And that's good for us because we want to study this harp in a elliptical orbit. You can basically run across the whole harp and hear all those different pitches, all those different strings. And what you'll see then is as the satellite moves away from the earth on its orbit, you'll hear a descending tone. And then as it moves back towards the earth, you'll hear the tone come up and pitch. It's kind of going back and forth along the harp.

That's a perfect, ideal harp sound. Of course, in a real event, you're going to hear all kinds of different stuff. You're going to hear on top of that crunches. You're going to hear all kinds of chirps and other things happening. And that's part of why we want to work with volunteers, it's to pick out these these really unique patterns that change from day to day. Yes, the team needs your help. The Themis satellite has been collecting data for over 15 years.

That's a lot of sun data. But don't worry, it doesn't take that long to listen through it as a volunteer. The waves harp is dealing with are ultra-low frequency, like most waves from the sun. Which means they're so low in pitch that you can't hear them normally. The team speeds them up, so they're in the frequency range your ears can hear, which has the added benefit of letting you listen through hours, even days of data, in seconds. You know, we have a lot of research that's been done. You know, individual scientists over the years and groups of scientists have learned a lot about these waves.

We've learned about the types of instruments that are in this kind of symphony in the near space environment. We've learned that there are things like the harp or like these magnetic strings or guitar strings. We've learned there are things like a drum, like that outer boundary that the sore one is pushing on. It's kind of like a drum. You can tap on it and you'll play different pitches, or different types of pitches. Scientists have identified many of the different instruments in the Solar Symphony, but they don't yet understand its music.

All the different combinations the symphony can play in, the patterns and pitches and amplitudes and intensities that can tell us so much about the solar wind and magnetosphere. There are these, all these patterns that are there that, you know, if someone just listens to the data, they pick out right away. You know, you listen to a year's worth of, data you'll ultimately find these complex but repeatable patterns in the sound that you wouldn't

have known to look for if you just looked through visually. So that's why we need people's help. I mean, they can go through a lot of data fast, getting more people's ears on the data and the eyes on the data too because you can also see the data on our website. So the more people that can look at this, the better. Your ears and eyes are a lot better than computers at finding patterns in harp data. Citizen scientists listening to harp sounds have already made a new discovery. unique reverse harp sound that researchers didn't expect at all. Can you hear the difference?

Sonification has also revealed a new sound in the solar wind and magnetosphere data that's not harp-like at all, but one that may sound familiar. Here's Robert again. A lot of features in the solar wind sound like chirping birds. There is an analysis example from the Themis satellite where there were these big features in the spectral plot. And there's this tiny little feature up top that wasn't really visually interesting, but when we played it back, we heard this kind of chirping bird sound. So we hear that kind of whee-z-you. That sound turned out to be several types of wave superimposed in the magnetosphere, a rare find.

It's a lot harder to pick that phenomenon out by looking at a chart. And the reason why it stuck out in auditory analysis was because it was just acoustically interesting. You don't expect to hear a bird chirp in the middle of your magnetometer data, your electric fields data. So that tells us that there's something unique that's going on. If you start listening to harp data, there's no telling what you'll find. As human observers of the universe, we can use our senses together, sight and sound to better understand our life-giving star and the space beyond. One thing I always tell people about this is, you know, magnetism. and electric fields and the stuff that we study is invisible.

And it's equally valid to use sound as to use visual. I mean, we use visual representations of things like graphs with like wiggly lines. But there's no, it's arbitrary, right? Like there's no reason you have to interact with that data visually. You can totally do it with sound and there's, it's an equally valid way of interacting with it. And in fact, you see different patterns with both of those. You know, and you go outside any given day and you close your eyes and just listen to what the birds are doing. Without even opening your eyes, you can tell what's going on.

can tell what's going on. You can tell if there's a hawk that just flew by. You can tell if there is a nest nearby. You can tell if a human is walking by. I mean, and I think it's the same with space sounds. You can learn so much about the environment just by listening to these sounds played through a speaker. The more tools we have at our disposal to study waves in space, the more accessible science becomes, better including scientists and citizen scientists who have limited vision or hearing. Science, like space, is for everyone. When we use our eyes, we can pick up certain things from a plot or a graph.

For a lot of people, they see a graph and it just kind of shuts them off. When we listen to an audio file, it tends to peak our curiosity, and we can pick out a whole slew of other details. We can hear glistening high frequencies and rumbling low frequencies. When we get up out of bed in the morning, we don't decide am I going to use my eyes or my ears today. We live in this multi-sensory world, and by turning data into sound, we're just using a sense that's more optimized for frequency analysis to conduct frequency analysis. I think it's incredibly important that human beings have this very intimate connection with the data that's gathered by satellites.

Just like stethoscopes allow doctors to hear the human heart. we now have these satellites that allow us to listen to the heartbeat of the sun. And I think so much of the investigation that takes place is driven by human intuition. And our human intuition can be an invaluable tool when it comes to the process of scientific research. The sun sounds like a lot of different things. Like really low buzzing. Kind of like when you're at like, lifting off on the plane or like when a jet's taking off or maybe it sounds like a lot of

rain falling down it sounds kind of like like a lot like fire maybe a fire or birds flying like if you turn your like head in a certain way or stick it out off a window and the wind goes on it it sounds kind of like that too sandstorm I think you guys are all right. So it sounds like a rain-filled, fiery sandstorm, right? Ampeats coming, and then here comes a sandstorm. And then we get the hum up the wind. And then the rain.

Wow, thank you guys. This is NASA's Curious Universe. This episode was written and produced by Christian Elliott. Our executive producer is Katie Conan's. The Curious Universe team includes Jacob Pinter, Maddie Olson, and Michaela Sosby. Our theme song was composed by Matt Russo and Andrew Santaguita of System Sounds. Special thanks to Alessandra Pesini at NOAA. Denise Hill and the NASA Heliophysics team.

All the Heart Project volunteers who sent us voice memos? Kirstie Beaton for her harp music for the Heart Project. Henry Dellinger for the use of his Cosmic Cycles Symphony. And scientists at the British Antarctic Survey and the University of Iowa's space physics department studying space weather for the whistler and chorus wave sounds. If you'd like to lend an ear to harp, go to listen.spacyscience.org

and start listening to the sun today. And if you enjoyed this episode about the sun, stay tuned. We've just entered NASA's heliophysics big year. As the sun approaches its solar maximum, there'll be opportunities to see solar eclipses and other amazing phenomena. And there's even more good news for sun lovers. We here at Curious Universe are working on a heliophysics-themed

mini-series about all things solar, coming to your ears next spring. If you like NASA's Curious Universe, please let us know by leaving us a review and sharing the show with a friend. And remember, you can follow NASA's Curious Universe in your favorite podcast app to get a notification each time we post a new episode. Sounds like robot frogs talking to each other underwater. Zippers. Zippers under water. It's just very fast. It sounds like you like pouring water, but like in time lapse or something, and I've never heard anything really like that. That is a weird sound. Yeah. Yeah, it is a weird sound.

It also sounds like my friends walkie-talkies when they get close to each other. One, two, three. Gurgly. Wait, what is gurgly sounding? It sounds like, here, if you get me some water, I want to show you. I can do breath before you do it, okay? Hey, Curious Universe listeners. Are you interested in more great stories from NASA?

Our friends over at NASA TV have a big announcement. NASA is launching an on-demand streaming platform. It's called NASA Plus. You can watch NASA's Emmy Award-winning live coverage, new original TV shows, and even listen to podcasts, all in one place. The best part? There's no subscription required, and it costs nothing. You can find NASA Plus on most.

major platforms through the NASA app on iOS and Android mobile and tablet devices, also on streaming media players like Roku, Apple TV, and Fire TV, and online on all kinds of desktop and mobile devices. You can download the NASA app now and be one of the first to get NASA Plus when it drops. Stay tuned and stay curious.