Ep. 467: Resonance

We’re recording on Sunday, Nov. 19 this week due to Pamela taking a well-earned vacation next week! Join us at a special time – 2 pm EST/ 11 am PST / 19:00 UTC for this episode!

Many of the moons and planets across the Universe are in resonance with each other and their star. What causes this resonance, and how can it help us understand the history of planetary formation and migration?

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This episode is sponsored by: Hello Fresh

Show Notes

Resonance definition
Tacoma Narrows Bridge (1940)
London Millennium Footbridge
“Brown note”
Orbital resonance
Orbital resonance paper
Nice model
Galilean moons of Jupiter
The Trappist-1 System
Fabry-Perot interferometers


Transcription services provided by: GMR Transcription

Fraser: Astronomy Cast, Episode 467, Resonance. Welcome to Astronomy Cast, your weekly fact-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. My name is Fraser Cain. I’m the publisher of Universe Today. With me is Dr. Pamela Gay, the Director of Technology and Citizen Science at the Astronomical Society of the Pacific, and the Director of CosmoQuest. Hey, Pamela. How are you doing?

Pamela: [Inaudible] [00:00:34].

Fraser: Good. We are recording this episode at a funny time. Where are you off to now?

Pamela: I’m actually going to go on vacation before the marathon of astronomy – that is what our reality is every winter – begins. So, I’m actually going to go hang out with some of the people that we’ve met through our various Astronomy Cast trips over the years. So, I’m going to go to Disneyland, and Universal Studios.

Fraser: On the West Coast.

Pamela: On the West Coast.

Fraser: Right.

Pamela: And, yeah, so I get back and jump straight into the marathon that is helping my colleagues, who are going to the American Geophysical Union, prep for that conference; prepping myself to go to the American Astronomical Society Meeting.

Fraser: Right. When’s the next AAS meeting?

Pamela: It is the second week of January in Washington DC. I will be there this year. I’m going to probably have a small fleet of students with me. We’re still getting permission from their professors. So, it’s going to be all science, all the time. And, I just wanted to get a little vacation in before I do that.

Fraser: That sounds great. You’ve earned it. I permit it.

Pamela: Yes. I needed me some Disney.

Fraser: I’ve been to that place three times, I think – Universal Studios – three times.

Pamela: I’ve never been to Universal. This is going to be my first time there, and I have to admit, I’m the kind of nerd that I tried really hard to find raven claw leggings before I go, and they only make them for, like, 12-year-olds, and I’m not 12.

Fraser: Well, have a great time. I just want to remind everybody who is listening to this podcast as an audio podcast – the regular stream – you are actually only getting half the show. So, we actually do a full hour of the show. Half of the show is what you’re listening to, but the other half is we just stick around and answer peoples’ questions. We talk about news. We talk about philosophy; things that are happening in our world. So, if you want to hear more of the banter, that’s in the full feed. And, somewhere there are instructions on how to access the full feed.

But, you can do a search for it. Astronomy Cast, the full feed. You get the raw recording experience. If you want more of the content, and more of the up-to-date news stuff – things like that. So, check that out if that’s what you want. Also, give us some kind of ratings and likes on iTunes, and all of the various social medias. That helps a ton.

Pamela: That’s all we want for the holidays. All we want is good reviews.

Fraser: All we want is good reviews. Or, bad reviews with constructive feedback.

Pamela: That’s true. But, if you can email those.

Fraser: Many moons and planets across the universe are in resonance with each other and their star. What causes this resonance, and how can it help us understand the history of planetary formation and migration? Resonance. And, this topic was recommended last week during our live show, and it was like this gap in our armor that we had not – We talked about planetary migration. We’ve talked about formation, and stuff, and we talked about the moons of Jupiter, and things like that, but we haven’t actually gone into this idea of resonance. And, a lot of it is fairly fresh in my brain.

I’m doing an episode of The Guide To Space about planetary migration, and talking about resonance. It’s a really fascinating topic, and comes up time and time again in astronomy, so I’m amazed that we haven’t done a whole episode of this – which is great. I love it. So, let’s do it. Resonance.

Pamela: The best place to start, I think, is just: What is this concept of resonance? Essentially, it’s that if you add energy to things at a particular frequency, you can drive their behavior. My favorite example of this – because it is so counter-intuitive – is swings in a swing set. If you have two side by side swing sets – One of the cheap, short ones that you get, and put in your backyard as a little kid. And, then one of the really tall ones that they have in schoolyard. Those two different sets of swings will swing the kids at very different rates. And, it doesn’t matter how far back you pull the child. The rate at which the swing swings is determined strictly by how long the chain on the swing is.

And, if any of you know of someplace that has baby swing set next to giant swing set, and you can recreate this experiment. I want that video desperately. So, please send us your videos of swing sets side by side. Or edit together side by side swing sets swinging; swings. We want this for the sake of science.

Fraser: Of science. We actually have a swing set on the local mountain nearby here on our ski hill, but it’s like an adult sized – like, it’s a super swing. So, it’s probably maybe 6 meters tall, so it’s a huge swing. So, when you’re swinging, it gets kind of terrifying as you’re going back and forth. So, total – another rabbit hole. So, how does resonance play into this idea of swinging? What is going on? What is the resonance part of this?

Pamela: So, with a swing set, you have this set, natural frequency of the swing. And, if you want to get a kid going at a higher and higher swinging swing – a higher swing of their swing. – I’m not quite sure how to verb that. If you want to do this, you have to provide energy to them at the same frequency at which they’re swinging. If you try to add that energy in anywhere else, you’re just going to screw up the system. So, imaging you were chaotically running underneath the swinging child, and randomly adding energy to their swing at all sorts of different intervals, you’re probably not going to do anything to successfully get them swinging higher and higher.

Fraser: Right, and I think we’ve all experienced that when you get the timing wrong, and you get the wind knocked out of you as opposed to gently adding a little bit of speed to the person swinging.

Pamela: And, this idea that if you regularly add energy at the correct frequency, you can end up greatly changing the behavior of the system. This is where resonance comes in.

Fraser: Okay.

Pamela: So, we have seen many different examples of this in the physical world. The Tacoma Bridge is one of the great examples they make all of us watch in school.

Fraser: Yeah. We watch that in engineering.

Pamela: Exactly. So, the period of oscillation is related to the length of something, and the power of gravity. And, bridges are basically a long string, and you can pluck them just like you can pluck a guitar string. And, if you add energy to them at just the right frequency, they will oscillate. And, in the case of the Tacoma Bridge, it oscillated itself into oblivion. It collapsed and died. And, there was actually the London Foot Bridge over the river – it also had the flaw that human beings tend to naturally walk with a set frequency.

And, its resonance frequency happened to match that of human beings walking, and so people were actually feeling ill, and the bridge was vibrating from all of these footsteps driving oscillations in the bridge. So, we have to be careful to not add energy into things, or to purposefully add energy into things at the correct frequency. With human beings, last week you brought up the concept of this brown note where human beings have a natural frequency ourselves. We are, after all, nothing more than a string filled with water. Well, scientist after scientist has tried to find a frequency that if you blast human beings with sound waves, dire things will occur.

I will leave the user to figure out on their own what brown note might mean. Now, no one has ever succeed in making anyone have horrible, automatic, gastrointestinal reactions in the downward direction. Yes.

Fraser: Yes.

Pamela: However, what has been found is that you can cause nausea. You can cause shortness of breath because of the way that the air is getting resonated inside the human. And, NASA being NASA – they knew that it wasn’t air that would be conducting the resonance to their astronauts. It would be the seat of their pants. So, they took the early astronauts, and stuck them in a chair, and resonated the early astronauts physically, and found that you can make them feel quite nauseous, and you can make it hard for them to think; hard for them to move because you’ve hit the natural frequency of the human being.

Fraser: Right.

Pamela: So, don’t do that.

Fraser: Don’t do that.

Pamela: Just don’t.

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Fraser: So, let’s talk about some other situations, and the one that I, sort of, intro-ed was this idea of orbital resonance. So, how does the resonance of planets and moons match swinging on a swing set?

Pamela: So, it comes down to this idea of adding energy to something in a systematic way. If you’re going along happily in your orbit, and you ever so randomly hit the gravitational pull of other objects at various places in your orbit, it’s probably not going to have a sum of all of these things affecting your orbit in a meaningful way. Now, if every single time you hit the exact same place in your orbit, you have energy added due to an extra bit of gravitational pull from another object. Over time, this is going to increase or decrease your orbit, depending on how it’s happening.

Now, what’s kind of amazing is because of all of the conservation factors that go on, it’s a matter of if you look at how does this gravitational force, acting over a distance, change/exchange energy, do/work? And, you also have conservation and momentum coming in. So, all of the cool physics, you can give really evil homework problems with this. And, the bulk result is you take a planet – call it Saturn. You put it into resonance with Jupiter so that the two of them keep lining up around the sun at the exact same place.

Fraser: Right. So, Jupiter will go around twice for every time that Saturn goes around once.

Pamela: And, then you litter the solar system with small things – asteroids, comets, rocky things, icy things – things that are between rocks and ice that we don’t know what to call because we lack imagination. You litter the solar system with all of these things. As they have their orbits changed systematically, they give up their angular momentum to these planets. So, if something keeps getting shuttled around by Jupiter and Saturn – let’s say Saturn is the primary instigator here – it’s going to get flung into the inner part of the solar system, and due to conservation of angular momentum, Saturn is slowly going to migrate backward getting further and further out.

And, it’s believed – through the Nice model, which is named after Nice, France, which is why it looks like the word nice, and is not pronounced that way.

Fraser: Yeah.

Pamela: – That there is this point in our solar system’s history where we had the giant worlds, and all of these different resonances, and a solar system that was still filled with stuff, and due to a combination of all of the stuff that they had to fling, and these orbital resonances, the world’s got moved outward. The stuff got moved inward, and the inner worlds got thwomped violently due to what we refer to now as the Late Heavy Bombardment.

Fraser: Right. So, there’s a neat – We talked about this at the end of the show last week, and it wasn’t in the regular feed – but, this idea that for many of the planetary systems, the perfect simulated version of this is that you have this big disk of material, these heavy planets are born and scoop up material inside this region, and then they sort of kick out objects that they encounter that have gotten a little bit bigger. And, as they kick them out, this causes them to lose orbital momentum, and they spiral inward until they reach, sort of, a clear spot in the solar system. And, then they stop.

Pamela: Or, hit something.

Fraser: Or, hit something. Sure. Right. In the simplified version. And, then you get, sort of, the next planet out moves in, and what puts the breaks on those planets from moving any further in is this orbital resonance. Once they hit this orbital resonance, that’s when they settle down. So, for a lot of the planetary systems that people are finding out there – especially for the ones that are close in to their red dwarf stars, you’re seeing these orbital resonances. When the forces of gravity are so strong, things line up and get into this balance. This music.

Pamela: And, we see this with the Galilean moons of Jupiter quite clearly, and this is actually the kind of observational experiment that anyone with even a moderately sized telescope can do for themselves where when you look to see how all of the happy little moons line up, there’s this Io going around – zip, zip, zip. Then, you have Europa going around, and it’s 2 to 1. You have Ganymede and 4 to 1, and Callista is in there as well, but I don’t remember what Callista’s resonance is. So, with this fabulous set of resonances, you have beautifully circularized orbits. You have tidal heating – which is what allows Europa to have these vast oceans, and Io to have these amazing volcanoes. And, it’s just awesome.

Now, unfortunately for the planets, while it was awesome, it was also highly destructive. You might be thinking how much momentum can one little icy body give up. So, when you look at our asteroid belt, our asteroid belt has the total amount of mass of about – I think it’s .4 of the moon. Now, all of the stuff that is theorized to have been flung around in the Nice model was actually 35 earth masses. So, we’re looking at tens, upon tens, upon tens of times the amount of mass that is in the asteroid belt was flung into the inner solar system.

Fraser: Yes, helping to cause the bombardment. And, this is the point is that these worlds – the process of getting into that level of resonance – you either get in line, or you get out. But, in the end, the amazing thing about the planetary formation and migration in our solar system was that because there was so much material, and there was so much chaos, and sort of mayhem that happened, they couldn’t settle down into that perfect orbital resonance.

They got as far as they could go, and then they just ended up in the place where they are with everything cleared out – and, not having the resonance. And, so things are strange. Like, Neptune is bigger than Uranus, but it’s farther out. The worlds are more spread out than they should be. They’re not as far packed into the sun as they would be if things were clear, and things were more stable, and happened better. They couldn’t reach that resonance that they wanted to because of all of this debris.

Pamela: And, according to this one particular model, the outermost worlds started out at 17 AU, and that outermost world was probably Uranus. Neptune and Uranus somehow got flopped in which one is further out. And, we ended up with Neptune out at 35 AU. So, it essentially doubled the distance of where the outermost of the known worlds is. Now, what’s going to be interesting is to see how things change, and how this model has to be upgraded as it is required to take into account the new world that we’re desperately trying to find that is causing Sedna, and everything else, to have such wonky orbits. So, this is Michael Brown’s team that’s doing these observations.

And, then there’s also computer simulations going on because when the Nice model was done in 2005, first of all, it was one of our first episodes of Slacker Astronomy, so you can hear us squeaking about it happily in Slacker Astronomy if you go dig out the episode. But, second of all, computers were not as good in 2005 as they are today. And, folks like our friend Kevin Glazier have been working on doing more modern models that are better able to take into account all of the different pieces; all of the different probabilities; and essentially do a much more fine grain simulation.

And, first of all, there may have been a whole lot more stuff that got expelled because it doesn’t really make sense that the stuff was only flung inward. We know that today, Jupiter is an equal opportunity destroyer, and sent things outward, as well as inward. And, when you take this into account, how does this change planetary migration? When you add in this new world, how does that change the models? So, we have a lot of new stuff, and I for one am eagerly awaiting to see what new simulations come up with in the future. But, we know that resonance is a thing because we do see it all over the place.

Fraser: Yeah, and a good example of that is the Trappist-1 System, where it has all of these worlds, and they’re orbiting quite tightly and close to their star, orbiting around and around, and they’re in a resonance. And, there’s a really interesting piece of music that someone created where they put all of the planets, and made them be musical instruments, and you could hear the resonance as they go over time. It absolutely sounds like music because it has these matched up beats, which music does.

Now, you talked about – this is one example, but I remember, even last week as we were setting this up, you were like, “Oh, and there’s masers.” So, there are some other topics in astronomy where resonance comes into play.

Pamela: So, we have the positive resonances of things that are like the Galilean moons; like the Trappist worlds lining up. We also have negative resonances. So, this is the Kirkwood gaps in the asteroids where if you try to find an asteroid that’s at 2.06 AU, you’re probably going to have a really hard time doing it because that would put it into a 4 to 1 resonance with Jupiter, and most of these Jupiter resonances – 3 to 1, 5 t0 2 – all of these different resonance for the most part are kind of mostly devoid of asteroids. So, we have asteroids that are taking away as well as asteroids that are adding things in.

Now, we also do find throughout the rest of physics, really cool effects of being able to use resonance to play with particles – to play with light, which is neither a particle nor a wave and is both a particle and a wave. Figure out however you want to phrase that. Figure out however you want to phrase that.

Fraser: It has a certain duality to it.

Pamela: It does. It is of mixed nature. So, when you’re building lasers, you have what are called optical cavities, that are designed to get all of the light going back and forth in a way that it resonates together. This is a super simplistic way of saying it, but the idea is basically you have an optical cavity, or a resonating cavity, and this creates waves of light the same way when you pluck a string you have waves on the string. Now, with a string on a guitar, you don’t have to worry about saying, “This string will not resonate if it’s the wrong length because the string adapts.” Light does not. Light is like, “I am green. You cannot un-green me. I shall not resonate. This cavity is the wrong size.”

So, you have to very carefully tune the size of your cavity to the color of the light you are dealing with to get the laser you wished to have. And, it’s just kind of cool that space, it turns out, has different ways of – in the micro wave – creating, basically, artificial cavities that allow space to generate the micro wave version of lasers, which is called a maser.

Fraser: The best name.

Pamela: And, those are just awesome.

Fraser: Yeah. So, there are these natural lasers – and, it’s essentially the same thing. Laser light and micro wave light are just two versions of light, just further on the electromagnetic spectrum. So, that’s amazing to think about that. – That the universe – I mean, we see it with orbital resonance with planets and moons, so it’s not surprising that this resonance appears in other times, and generates these things. But, it’s still a pretty fascinating concept. Did we do an episode on masers? I think we did.

Pamela: I think we did. Or, at least we brought them up within the context of lasers.

Fraser: What is the underlying mechanism of a maser?

Pamela: I was ready to jump to Fabry-Perot interferometers, and you went somewhere completely different.

Fraser: You want to talk about interferometers?

Pamela: I do. So, let’s jump from lasers to instead how you can actually subtract light instead of adding it.

Fraser: What?

Pamela: So, just like the resonances that we have with orbits can either taketh or giveth, where you either have things like the Galilean moons happily resonating and generating awesome, or the asteroid Kirkwood gaps that are happily taking away. With light, we have lasers which happily have this cavity that leads to population inversions awesomeness, and bright lights that we can use to torture cats who don’t understand they can’t catch light. We can also use this kind of resonance in what’s called a Fabry-Perot system, and interferometer [inaudible] [00:25:36] to remove light of unwanted colors. So, you shine starlight into a system that has carefully spaced surfaces that both transmit and reflect light in different ways.

And, what will end up happening is the only light that’s able to get transmitted through the system is stuff that has the correct wavelength for the given cavity size. So, you can tune this sucker to see different colors of light, thanks to cavity sizes, and resonance, and all of this awesomeness. And, it’s just kind of cool. And, this gets back at this dichotomy of interference, like we talked about last week; resonance, which we’re talking about this week, and how all of these different physical factors work together.

Fraser: One, sort of from space flight reporting that we dealt with back in 2009 – I just remembered this. But, the International Space Station has a resonance to it.

Pamela: Yes.

Fraser: Like any physical object.

Pamela: Yes.

Fraser: You said bridges, right?

Pamela: Yes.

Fraser: And, so there were these rockets attached on one of the modules, and they would boost the space station from time to time, and so the rocket was firing at the resonance frequency of the International Space Station, and the rocket kind of gimbal. So, you can watch this video, and you can see the whole space station jiggling, and the rockets kind of gimbaling around as it’s doing this orbital burn.

Pamela: And, they don’t do that anymore.

Fraser: No, I’m reading Endurance, the book by Scott Kelley about his year in space, and talking about how they – after that event, they’ve changed the way they boost the space station to try to avoid that resonance because if they just kept going, would things have shaken loose? So, still, it’s a problem out in space, and with rockets. You can imagine when the space shuttle is launched, they shake badly, right?

Pamela: Mm-hmm.

Fraser: And, a lot of the times, the pools underneath the space shuttles and stuff – a lot of that is their acoustic dampeners, and their job is to stop the sound waves from coming back up and hitting the rocket again, and tearing it apart. And, I don’t even know if you’re getting into resonance. You’re just getting into destructive damage of these acoustic waves that are being done to these rockets. But, the resonance would take it to the next level. You get that rocket shaking from its own sound, the thing will tear itself apart.

Pamela: And, what is so cool is they actually have at – I believe it’s Goddard – a vibration chamber that they stick things in that they’re planning to launch to vibrate the bejesus out of them in a safe environment where they can turn off the vibrations if they discover they’re hitting a resonance. And, they will change how spacecraft are packed; how they are folded up; what ballasts they have around them – to make sure that the common frequencies encountered during launch are not the frequencies that are going to shake apart spacecraft.

Fraser: One last thing, Gito is saying this in the chat, and normally I don’t bring this stuff into the episode, but he’s exactly right, which is the treadmill. So, the treadmill on the space station – when someone is using and running on the treadmill, it causes a resonance in the space station that has been of concern in the past, and so they have to dampen the treadmill so that it doesn’t shake the space station, which is just and amazing idea. Alright. We’re at the end of our time. Pamela, thank you so much for talking about resonance this week. Have a safe trip, and we’ll see you next week.

Pamela: See you. Bye-bye, everyone.

Male Speaker: Thank you for listening to Astronomy Cast, a non-profit resource provided by Astroshpere New Media Association, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at AstronomyCast.com. You can email us at info@astronomycast.com; tweet us at Astronomy Cast; like us on Facebook; or, circle us on Google Plus. We record our show live on YouTube every Friday at 1:30 p.m. Pacific, 4:30 p.m. Eastern, or 20:30 GMT. If you miss the live event, you can always catch up over at Cosmoquest.org, or on our YouTube page.

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[End of Audio]

Duration: 31 minutes

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