Listener Questions #24

00:00:07
Speaker 1: If the Earth and Jupiter were to collide, what would happen? How would we die?

00:00:13
Speaker 2: Circadian rhythms are corrected using the Sun's light. If you live at the bottom of the sea, how do you get that right?

00:00:20
Speaker 1: How big a planet could we use rockets to escape? If we'd evolved on Jupiter, would we be planet down apes?

00:00:28
Speaker 2: Whatever questions keep you up at night, Daniel and Kelly's answers will make it right.

00:00:32
Speaker 1: Welcome to Daniel and Kelly's Extraordinary Universe.

00:00:37
Speaker 2: With an emphasis on Jupiter, it seems. Hello, I'm Kelly Wiersmith, and I study parasites and space, and clearly Jupiter is the best planet.

00:01:00
Speaker 1: Hi, I'm Daniel. I'm a particle physicist, and yes, Jupiter has the most particles of any planet.

00:01:05
Speaker 2: And does that make it the best As a particle physicist.

00:01:10
Speaker 1: It makes it the mostiest? I guess you know. I think people underestimate, like how much of the Solar System is just the Sun in Jupiter? Like mostly it's just the Sun, and then you want to add Jupiter, all right, to round it up to nine to nine point nine, and everything else is just details. We're really just here in somebody else's party.

00:01:28
Speaker 2: Oh, man, that's a little it's a kind of a bummer of a way to start our episode.

00:01:34
Speaker 1: We are all insignificant, No, I think it tells you something though, when you look at the depiction of the Solar System and all the planets are like big, and obviously it's not the scale, but it tells you something about what we find important. Right, Clearly, we are important in the Solar System. So we zoom up. It's like that cover of the New Yorker where they show like a map of the United States from the New York City perspective, and it's like mostly Manhattan and then like a few details and that's ridiculous and you laugh at it, But that's exactly what we're doing about the planets, right.

00:02:05
Speaker 3: Well.

00:02:06
Speaker 2: But you know, on the one hand, we've known about Jupiter for much less long than we've known about Earth, and you know, we're here on Earth, makes it easier to study. I'm going to go ahead and stand down on defensive Earth and the Earth centered view of the world.

00:02:20
Speaker 1: I'm the saying it's wrong. I'm just saying it reveals something about our biases, right, the things we think should be presented first.

00:02:27
Speaker 2: I grant you that, but there's probably, you know, solar systems that are bigger than ours, and maybe we shouldn't even be talking about our solar system at all. And where do you stop, Daniel, Where does it end?

00:02:37
Speaker 1: It never ends, Kelly, There's no bottom to the philosophical rabbit hole.

00:02:43
Speaker 2: Oh my goodness.

00:02:44
Speaker 1: But we love going down rabbit holes, especially rabbit holes that you are interested in. So if you have a question about the nature of the universe, or how something works, or how little squishy critters make their lives, please write to us with your question. We would love to answer it here on the pod. And today we're answering three super fun questions from listeners.

00:03:03
Speaker 2: That's right, so let's start with our first question from.

00:03:05
Speaker 1: Brad, A great question about Jupiter, of course.

00:03:09
Speaker 4: Hello, Daniel and Kelly. I have a question about planetary collisions. Jupiter is classified as a gas giant planet and is known to sweep up many stray masses flowing through our Solar system. If something were to happen to cause Earth and Jupiter to collide, what would happen at impact? Is the mass of Jupiter large enough to spaghettify Earth and destroy us like a black hole? Or is the likelihood of a direct collision too small, and Earth would just be ejected from the Solar System if we become too close. Or is the surfaces of Jupiter really a gas and Earth would just pass into the inside of Jupiter and basically be absorbed, and Earth would just coast through a dense atmosphere of gases and would eventually hit a solid core. Thanks Brad from League City, Texas.

00:03:49
Speaker 1: So, Kelly, do you think Brad is a supervillain planning to push Earth into Jupiter or threatened to?

00:03:54
Speaker 2: You know, I did wonder about that when I was listening to this question. I'm a little concerned, and you know what, a little concerned in general now that this is something you know on my radar to worry about. And then too, I'm a little worried about Brad in particular.

00:04:08
Speaker 1: A couple of red flags here. Yeah, I'm not sure in his question if he's worried about this or excited about it, He's like, let's do the experiment.

00:04:15
Speaker 2: Yeah, yeah, hard to say, hard to say. Maybe we shouldn't give him the answer m exact.

00:04:22
Speaker 1: I worry about that. Like when the kid wrote to me and asked me what it would take to blow up Mars. I was like, hmm, should I really be telling a ten year old how to destroy a planet?

00:04:31
Speaker 2: Well, but on the other hand, you know, you hope they don't wield that sort of power, didn't do anything about the information.

00:04:36
Speaker 1: Who knows what today's ten year olds will do in twenty or thirty years.

00:04:40
Speaker 2: Right, that's true, that's true, and you'll beat a blame, Daniel, accept that blame.

00:04:46
Speaker 1: But today we're here to answer Brad's question as a hypothetical science question about something we hope will never happen, which does reveal a lot of really interesting solar system physics. So let's get into it.

00:04:57
Speaker 2: And I think we should probably start with what is spaghetification because that is clearly one of the best scientific terms our community has ever come up with.

00:05:05
Speaker 1: Absolutely. Spaghetification is usually used to describe what happens to an object as it approaches a black hole, in that you won't just fall in, you'll be torn apart into spaghetti essentially before you actually fall into the black hole. And this doesn't just happen around black holes. It happens all the time in strong gravitational environments. In fact, it's happening to you, right now, and it's happening to the moon. It's the result of tidal forces. And the reason simply is that the force of gravity depends on distance. So if you're falling into a black hole or you're orbiting a planet or whatever, and your feet are closer than your head than your feet have a stronger gravitational force on them than your head does, and effectively, that's a force pulling your feet away from your head. And if that force is strong enough, it will pull your head off your body or your feet off of your head, depending on your perspective.

00:05:55
Speaker 2: I'm going to be honest here, I feel like you've sort of de excitified spaghetti cation for me by being like, it's just a kind of title force. It's like, what's happening.

00:06:04
Speaker 5: To the moon.

00:06:04
Speaker 2: And I'm like, oh, but I'm spaghetific. That's not what I imagined in my head.

00:06:08
Speaker 1: Uh, you're imagining some sort of black hole magic.

00:06:11
Speaker 2: Yes, yes, I thought this was a specific black holy thing and that spighetification really, you know, required you to be thin like a noodle.

00:06:19
Speaker 1: But okay, physics has been ruining things since fifteen eighty four or whatever.

00:06:23
Speaker 2: Oh, and what happened in particular in fifteen eighty four. Daniel I just.

00:06:27
Speaker 1: Made it that date. I was referencing one of Zach's comics.

00:06:31
Speaker 2: I can't remember what year he had on this or why he picked it.

00:06:36
Speaker 1: I think it was supposed to be like Galleo's experiments or Bacon or somebody like that. Anyway, the point is that tidal forces are a thing. So if you approach Jupiter, for example, then the difference in forces between one side of your object and the other side of your object, those are the tidal forces. And that's why we have tides on the Earth, because the Moon pulls on one side of the Earth more strongly than on the other side of the Earth, making it a little bit of a football, and the Earth it's the same thing to the Moon, and that's why the Moon is locked in place. It's called tidally locked because there's a little bit of a football and it's hard for it to spin away from having the point a bit of its football aligned with the point a bit of the Earth's football.

00:07:12
Speaker 2: Okay, but so Jupiter is much bigger than the Moon, so is you know you said that when the force gets hard it could like pop a head off. Is Earth's metaphorical head gonna pop off towards Jupiter or is it just gonna get like weird tides.

00:07:27
Speaker 1: Yes, So there's a boundary called the Roche limit. If you get closer than that, you get torn into pieces. If you're further away from that, you don't. And that's why some planets have rings and some planets have moons. If your moon is further away than the Roche limit, it stays together. Local gravity winds over the tidal forces. If you get too close, then it gets torn apart into a ring because the tidal forces overcome the internal gravity. So that's the Roche limit. So what happens as the Earth approaches Jupiter, Well, the roach limit for a solid body like the Earth is actually inside the cloud tops of Jupiter. Jupiter is a gas giant, and the outer layer is like fifty kilometers of just clouds blow which you have like gaseous hydrogen, and then liquid hydrogen, and then this crazy helium neon rain, and then ocean of metallic hydrogen before you get to the icy, rocky core. So the Earth would sink into the clouds without getting torn apart. It would get torn apart after it already passes into the clouds.

00:08:25
Speaker 2: Okay, So at that point we are closer to Jupiter than Jupiter's rings. Right, So Earth's not going to become like a ring of Jupiter. It's going to get torn apart and then rain down on Jupiter. Is Jupiter the planet that has the diamond rain?

00:08:39
Speaker 1: I think that's Saturn. Ah, it is so disappointing thing. Yesh, Jupiter, yawn.

00:08:45
Speaker 2: Come on, Jupiter, step up your game man.

00:08:49
Speaker 1: All right. So now we have a collision of an entire Earth, right, it's whole. It has not been pulled apart by the tidal forces of Jupiter, and it hits Jupiter, and Brad asks like, what's going to happen? And is it going to pass in and be absorbed to hit the solid core? And you're definitely not going to make it all the way to the solid core because even though Jupiter is a gas giant, it has like layers and layers of hydrogen. That hydrogen is dense, and atmospheres have friction. Even here on Earth, where atmosphere is pretty low density compared to the Jovian atmosphere, you know, there's re entry. If a rocket or an asteroid tries to enter the Earth's atmosphere. There's a lot of friction from the atmosphere and you get all this heat, and most things that hit the Earth's atmosphere don't make it to the surface. Same principle applies when the Earth hits the Jovian atmosphere. Okay, and so what's going to happen is you're going to compress the Jovian atmosphere, which is going to heat it up, turn it into plasma, and that's going to vaporize the crust and the mantle of the Earth. Yeah. Bad, And so essentially a massive energy release. Here did a little bit of the back of the envelope calculation, and assuming that the Earth hits at like sixty kilometers per second, which is, you know, fast but not super fast for Solar system speeds, you're gonna release ten to the eighteen megatons of TNT. Wow. And you might be like, I don't know what that number means. Well, the Hiroshima explosion was fifteen kilotons. This is ten to the eighteen mega tons. So it's like so much bigger. And you know, I mean the entire Earth is essentially a bomb, and a lot of that mass is converted into energy. So it's an enormous explosion. You're gonna get like a fireball rising above the surface of Jupiter. It's gonna be much bigger than the volume of the Earth. And you're gonna have shock waves in the Jovian atmosphere which probably will last for years. You may even leave a spot on Jupiter. It's very unlikely you're gonna make it all the way to the core because you've got lots of dense layers before you get there. But yeah, it's gonna be a huge impact. But remember Jupiter is huge compared to the Earth, Like, it's so much bigger than the Earth that even though this is an enormous amount of energy and would devastate the Earth vaporized essentially, Jupiter is gonna mostly shrug it off.

00:11:00
Speaker 2: Oh man, that's a little insulting. Every human I've ever known or loved disappears and Jupiter's like, eh, okay. Well, so say at this point, when this happens, we have a self sustaining settlement on Mars. If the Martians were like in the right position, could they see this or would the act of Jupiter moving towards Earth have destroyed Mars on the way or thrown Mars off orbit. This is probably unfair. It's a totally different question. But am I asking you anyway? Daniel?

00:11:29
Speaker 1: Oh? I see well, I was imagining that the Earth is getting tossed into Jupiter. Read when Jupiter is like bullying its way into the inner Solar system. Oh okay, so the Martians have a nice view of Earth shooting by and then they yeah, they could watch Jupiter as it gets impacted. In fact, we had ringside seats to a similar event in the nineties.

00:11:46
Speaker 2: And I think you told me that you were at a telescope watching that, right, Yeah, I.

00:11:50
Speaker 1: Had a super fast camera hooked up to a telescope to watch this collision. This is in the mid nineties comet Shoemaker Levee impacted Jupiter and created all these fireballs. Now the comet not nearly the size of the Earth, of course, but still very very dramatic. And what happened is that this comet, which used to be orbiting the Sun, got captured by Jupiter. So now it was orbiting Jupiter sometime in the sixties and in the early nineties it passed very close to Jupiter, so Jupiter tore it apart. It went within the roch limit, not actually within the clouds. The roach limit weirdly and confusingly depends on the object, Like if you're made out of diamond, then your rochal limit is much closer. You have to get much closer to get torn apart than if you're made out of like cotton candy. Right, And so this comic got torn apart into twenty one pieces, which they labeled ABCD all the way up to w NASA.

00:12:39
Speaker 2: Very creative, of course they did. That was an opportunity for creativity. So they had to pass it by and.

00:12:44
Speaker 1: Then it's swung around one more time, and over six days in nineteen ninety four, each piece took turns smacking into Jupiter. Wo really amazing, and everyone on Earth was like turning their telescopes to it and watching these pieces hit. And the biggest spot is the one where the g fragment hit, and so you can imagine what that spot might be called.

00:13:03
Speaker 2: I was just thinking that, but this is a children's show.

00:13:07
Speaker 1: Exactly, and created a huge dark spot. There was a fireball and a dark spot the width of the Earth.

00:13:13
Speaker 2: Wow.

00:13:13
Speaker 1: Right now, this fragment is a piece of a comet, which is tiny compared to the Earth, but it created a big spot the size of the Earth that was visible for a year. So we've seen this kind of impact much smaller, So essentially you just scale this up much more dramatically, but still small compared to Jupiter.

00:13:28
Speaker 2: Amazing. I wish I had watched them. That wasn't on my radar because I didn't have amazing friends like you back then. You wouldn't have let me go astray. But that's all right.

00:13:38
Speaker 1: I was in college at the time, and I was home over the summer doing a research project on plasma physics, and we had a super fast camera that we were using to image what happened when you drop a little pellet of fuel into the fusion plasma. And the guy I worked for also had a telescope and he was like, let's point this thing at Jupiter. So he connected the camera to the telescope, pointed to Jupiter, and we had one of the fastest digital cameras around at the time for scientific applications, so we were hoping to have like the highest time resolution photographs of this impact. But just as the impact was going to happen, it went over the horizon, so we got pictures of the fireball rising over Jupiter, but not the impact itself. But it was a lot of fun anyway.

00:14:17
Speaker 2: So wait, this was ninety four though, is that right?

00:14:21
Speaker 1: Yeah?

00:14:21
Speaker 2: Okay, so I was twelve, so I probably I was listening to Silverchair and I didn't care about anything other than Silverchair.

00:14:30
Speaker 1: So important stuff, important.

00:14:32
Speaker 2: Stuff, ohs that way, at the time, the rest of us.

00:14:34
Speaker 1: Were learning about the future impact of Earth on Jupiter.

00:14:36
Speaker 2: But you know whatever, Well, I was having a good time, so I wouldn't change it for anything, all right. Brad asked if there was any chance we'd get ejected from the Solar system, But you didn't mention that as a as an option, so that's not something that would happen.

00:14:52
Speaker 1: It could happen, It depends on how accurately Brad and his supervillain team aim the Earth at Jupiter. One possibility is it hits Jupiter right. Another possibility is that it's captured and orbit Jupiter. And this has happened to a bunch of stuff. We think that many of the moons of Jupiter didn't form with Jupiter but were captured by it later. But it's a little bit unlikely because for that to happen, you have to be only at the right angle and the right velocity at the right location to get the orbital mechanics to work out. So more likely you're either going to hit Jupiter or you're going to get ejected from the Solar System because you're going to have a gravitational interaction with Jupiter, which is then going to throw you out of the Solar System.

00:15:27
Speaker 2: All right, well, one way or another. I think someone should be keeping a close eye on Brad and let's see if our answer changes Brad's mind about whether or not this is a good idea.

00:15:39
Speaker 4: Daniel and Kelly, I absolutely love this response. I assure you that I am not a supervillain and have no plans to destroy the planet. It sounds like we would get to watch as we pass into the gas cloud layer before we heat up and explode. I like to know that we would at least have a little impact on Jupiter. I think all we need to know now is where Michael Bay wants to set up the camera to catch it's the greatest collision of all the time. Thanks for all y'all do.

00:16:22
Speaker 1: All right, we're back and we're answering questions from listeners. Now we're going to take a break from Jupiter themed questions and think about sleeping. Here's a wonderful question from one of our Discord listeners. And if you're not on Discord, Colm, join us on our Discord channel. We have lots of fun conversations about science. We answer questions on there, other people answer questions on there. We have wonderful moderators to keep it a really happy fun family. Colm, join us for science chats on Discord. You can find a link on our website. Anyway, here's the question from our listener.

00:16:52
Speaker 5: In the episode about sleeping dreams, the topic of circadian rhythms in various animals came up. I was curious how circadian rhythms work in animals that never see the sun, like cave dwellers or various deep sea creatures. Thanks for taking the question, looking forward to the answer.

00:17:10
Speaker 2: Bye, all right, t to the j on Discord. I gotta say, you know, this question came in and I thought, all right, circadian rhythms. I'm a biologist. I should be able to knock this answer out pretty quick. I don't know anything about circadian rhythms. It turns out, oh no.

00:17:26
Speaker 1: This was biology is a big field.

00:17:28
Speaker 2: That's what I'm saying, but I really enjoyed the opportunity to get to dig into circadian rhythms again. This is one of the things I love about the questions we get from listeners. There's so many things I thought I understood and then they give me a chance to dig into them, and I learned so much. So uh, circadian rhythms. Circadian comes from the words circa diaz, which means approximately a day. And I'm you know, I don't know, maybe that's Latin. I probably pronounced it wrong, but you all know what I'm saying. So it's all right. We're good and nobody expects me to pronounce things right at this point.

00:17:58
Speaker 1: That's not what they're here for, Kelly, is not.

00:18:00
Speaker 2: What you're here for. So circadian rhythms are like internal rhythms that happen on an approximately twenty four hour cycle, and they're entrained or they're sort of like synced up based on outside signals like light.

00:18:16
Speaker 1: But why do you say approximate? I mean, the earth cycle is pretty crisp. Wouldn't we do best being closely linked to it? Why are you saying approximate?

00:18:25
Speaker 2: Because you know it's just not perfect and some people have cycles that are a little bit longer than twenty four. Some people have cycles that are a little bit shorter than twenty four. We think this contributes to why some people are mourning people and some people are night people. And then if you're talking about organisms other than humans, you can get some other slightly different sorts of signals that are approximately twenty four hours.

00:18:46
Speaker 1: So then what parts of the human body are affected by it? Obviously you sleep in this sort of twenty four hour cycle. Is there other stuff going on also?

00:18:54
Speaker 2: Yeah, lots of things. So like sleep is important, metabolism is also important. Like your body temperature is impacted by circadian rhythms.

00:19:03
Speaker 1: Right, metabolism, So that is that why I shouldn't eat chips at ten pm?

00:19:06
Speaker 2: That could partly be it or be involved. I think cortisol is to some extent involved in helping with digestion and stuff, and so your cortisol kind of peaks at times of day when you're like expected to be hungry and expected to be eating.

00:19:20
Speaker 1: What's cortisol?

00:19:21
Speaker 2: Cortisol is a hormone that folks usually associate with recovery from stress. So when you get stressed out by something, your body releases cortisol, and then cortisol helps your body sort of return to homeostasis or like a normal state after you've been stressed out.

00:19:36
Speaker 1: Cortisol sounds great, as you can say more of that.

00:19:38
Speaker 2: Well, if you are, like, you know, running away from a lion, cortisol is great, like it releases a bunch of energy all at once that you can outrun the lion, and then when you're in a safe spot, it helps you sort of return to normal. But if your cortisol level is elevated for a very long time, you can start having diseases because you're constantly in a stressed out state. So cortisol is more supposed to like get you out of an intent hence acute situation, but if it's elevated chronically, it can be bad. And there's a really interesting book on this called Why Zebras Don't Get Ulcers by Robert Sippolski. Cool.

00:20:10
Speaker 1: All right, yeah, well, I wonder if zebra's go to my physics faculty meetings if they feel stressed out and need cortisol afterwards.

00:20:17
Speaker 2: Oh yeah, faculty meetings. I think what I'm stressed out about in faculty meetings is that I could be spending my time way better doing anything else. But you know, I haven't had to go to faculty meetings for a while, so that's great.

00:20:28
Speaker 1: Dark wasn't Today is not about silly arguments and physics faculty meetings. It's about the rhythms of the body. So you're telling us that these things happen and impact sleep, metabolism, and temperature. But what's the mechanism for it? Like, what is driving it?

00:20:40
Speaker 4: Yeah?

00:20:40
Speaker 2: Okay, So most of the work that we've done to figure out the mechanism has been done in organisms like mice and fruitflies. But here's how we think that it works. How we're guessing that it works in humans based on what we've seen in lab animals. So there's a little part of your brain called the hypothalamus, and inside of the hypothalamis there's a little region called the super chiasmatic nucleus or the SCN. Because I'm not going to try say that a bunch.

00:21:03
Speaker 1: Of times it sounds a lot like super cool, fudulistic, expire audotious, but all right, yeah, I hear that every time you say that.

00:21:09
Speaker 2: Now, okay, no one's going to be able to pay attention to the rest of the episode. They're going to be singing just like Mary Poppins, but try to focus people, all right. So you've got the SCN, and the SCN is connected to the optic nerves, and so optic nerves these are the nerves that go to your eyes. And so we've talked in the past about how your eyes have specialized cells called rods and cones, and those help you detect like patterns and colors and to see your world. But you also have cells that just detect the intensity of light, and those cells send information through your optic nerve back to the SCN, and your brain uses that information to tell the rest of your body how the rhythm should be working. And so it does this by either sending messages through the nerves or by directing the production of hormones that will then go to the rest of your body and talk to your cells and basically say, Okay, hey guys, it's morning. And when it's mourning, your body increases, its heart rate, increases, its blood pressure, increases temperature. Your body is not making melatonin at this point. Melatonin is associated with sleep. So this is generally how your body collects the information about what should be setting the timing for the rhythm. But each one of your cells also has its own circadian clock.

00:22:30
Speaker 1: So we have these special cells in our eyes. Instead of just using the information which already exists in the rods and cones, we like evolve the separate pathway just for this. Wow, this is pretty weird engineering.

00:22:41
Speaker 2: Well, but it's detecting something different. Your rods and your cones are detecting like colors and you know, patterns of like dark against light and stuff like that. These cells are just detecting the intensity of the light that's coming in. So you're like, oh it's dawn now, or oh it's noon, and so it's detecting that.

00:22:59
Speaker 1: I feel like I could write a computer program to extract the same information from the data produced by the codes and the rods. But that's fine. Obviously the brain is not engineered by physicists.

00:23:09
Speaker 2: And that's not how evolution works. Evolution doesn't say, Okay, I'm going to start from scratch and come up with the best system. It's like, well, what do I have and how can I work with it?

00:23:16
Speaker 1: I just think it's a fascinating clue that something happened there that this is what we ended up with. You know, It's just another example of how like obviously this is not well organized. Just what kind of worked? And so do we know this because we've like done studies in mice where we've like tweaked those cells or got rid of those cells, or like shined light on those cells or something, and it's changed the way the mice behave.

00:23:37
Speaker 2: Yeah, so if you mess up a mouse or a flies SCN, then they'll start free cycling. So essentially they won't show these twenty four hour cycles.

00:23:46
Speaker 1: They're not so xpl a doocious anymore.

00:23:49
Speaker 2: That's right, that's right. It's truly quite atrocious.

00:23:51
Speaker 1: All right, So that's wrong. Okay, that was pretty good. That was really good.

00:23:58
Speaker 2: Grudgingly patting me on the back there.

00:24:00
Speaker 1: I was so excited about my next question. I didn't registering a joke, but that was excellent. Yeah, ten points for Kelly for everybody's keeping score. So you're telling us that not only these light signals tell us when to be fragilistic, but also the rest of our body responds in some way.

00:24:17
Speaker 2: Yeah. Okay, So first I just want to mention real quick that that organisms from bacteria to humans show these clocks, and so this is like not every organism uses their SCN and so this sort of like feeds back on our conversation about how you just use what you have. This has been going on for a really long time anyway. So not every single cell has its own circadian clock. I misspoke earlier, but many cells, even if you take them out of the body and you put them in like a petri dish, they will show like a twenty four hour schedule for the activities that they do, like they've repair DNA at a certain time, you know, stuff like that. And so here's how we think that works. So your cell is making a a protein called clock protein. The clock protein at dawn moves into your nucleus where the genetic information is stored, and it binds to literally thousands of different sites on your DNA. And when it binds, it's telling your DNA to start making certain things. And it could be making certain hormones, like it can say, hey, start making that cortisol. It could start doing you know, whatever is needed to increase body temperature or heart rate, et cetera. So thousands of things are turned on when your clock proteins go in there and bind to lots of different spots. Another thing that's being made. Though, during the course of the day are proteins that will shut this down. And these proteins are called period proteins, And so the period proteins will build up over the course of the day because the clock proteins said, hey, start making these, and at some point they've built up to high enough levels that now they go into the nucleus and they pull the clock proteins off of the DNA and that stops all of the stuff that the clock proteins had been turning on and getting made. As the night goes on, the period proteins break down and go away, and then the next morning the clock proteins go back in and the cycle starts again.

00:26:10
Speaker 1: So, like many clocks, you have some sort of process which has a natural timescale built into it, right, and so there is chemistry where things are slashing back and forth and naturally at the same rate as our twenty four hour cycle. Is that what's happening?

00:26:24
Speaker 2: Yeah, yeah, that's a good summary. And I saw you. Yeah cool looking something up? Was I wrong about something or was it unrelated?

00:26:31
Speaker 1: I was wondering if clock was an acronym for something in a really tortured way.

00:26:35
Speaker 2: But oh, okay, right, I.

00:26:39
Speaker 1: Was hoping it stood for something ridiculous. Okay, because if it was a physics acronym, it definitely would have a ridiculous name.

00:26:45
Speaker 2: Got it anyway, So light is important for determining these cycles, right, But it also is fine tuned by things like the temperature you find yourself at when during the day you're eating, and these cues are important for other animals as well. So it's not just light, but light does seem to be a super important factor.

00:27:02
Speaker 1: So it's interesting you have several different kinds of things going on. Can they get out of sync or is there something that tries to keep them in harmony.

00:27:09
Speaker 2: Well, so, once you develop a cycle, your body is pretty good at keeping that cycle going. So like if you stayed in a dark room for two days, your body would still have some of its normal cycle. It's not like it breaks down immediately, but over time, if you deprive your body of that light queue or you mess your cues up, then you can start having problems. So for example, if you work the night shift, you know, any of us who have had jet lag have had like a temporary period where circadian rhythm was like something's not right, and then it's had to get back to normal. But being off of your normal circadian rhythm too often, for example, working the night shift increases your risk of diabetes, obesity, depression, dementia, and some kinds of cancer. So these circadian rhythms seem to be important for a lot of reasons, at least for humans.

00:27:56
Speaker 1: Wow, and how widespread are circadian rhythm that everything on Earth has a circadian rhythm?

00:28:02
Speaker 2: Well, so like bacteria, humans, plants, lots of stuff has circadian rhythms. But our listener had a really great question, which is how on Earth do you have a circadian rhythm if you live in a place with no light? And so the three different situations that I looked into where there's no light are if you are, for example, at the North Pole during the time of year where you don't see the sun. There's like, I think a couple months where that's the case, if you live in a cave, or if you live in the deep sea. And then there's also organisms like naked mole rats that live underground. But I think naked molerats can peek their heads out every once in a while and see the sun to help in train their clock, so they get some light cues still, So let's start with if you live far north. So one thing that's important to note, which we touched on just a second ago, is that clocks don't go away immediately just because you're in total darkness. So at the start of the long night, they're probably fine because their body hasn't like forgotten the rhythm yet. And during the time of year when it's all light, they're probably also fine because the intensity of the light still changes over the course of the day, and your eyes are focusing on light intensity, not just whether it's there or not, so they can still keep their rhythms at that time of year. But there is a point in the winter where their clocks have not had appropriate input for long enough because it's been dark for so long, and they do seem to stop showing signs of twenty four hour cycles if you look at the reindeer, So it looks like at some point they do start free cycling essentially and their circadian rhythms start to break down. Wow, they don't seem to have physiological problems associated with that. I'm not quite sure why, but it looks like they do break down at some point, So.

00:29:47
Speaker 1: It's bad for them to be in the dark, like it would be better if they got light occasionally to sort of like correct their cycles or get them back on track.

00:29:54
Speaker 2: Yeah, So I was trying to figure out the answer to that, and I think that the answer is to some extent that it's complicated. So, you know, part of why we have cycles is that it helps us figure out like when we should be eating and stuff like that. And part of that, if you are a wild animal, is about when your food is even available, right, But if you're in the dark and all the other animals are in the dark all the time too, you might not need to have a circadian rhythm because it might you know, if you're, say you're a fox living in the Arctic circle, you want to make sure you're awake at the same time as the bunnies. But if it's complete darkness and everybody's free cycling, you don't really need to get up at a certain time because the bunnies could be out there at any time, and so it's not a helpful queue anymore to like have your activities sync to a certain time of day.

00:30:42
Speaker 1: I was wondering more about the internal stuff, Like you mentioned earlier that if your rhythm gets messed up your risk for diabetes and cancer and stuff. Is the same thing true for reindeer when they're free cycling.

00:30:52
Speaker 2: Yeah, so I don't know the answer for reindeer, but I did try to find the answer to that question. I was able to find some information about blind cavefish. So there are fish that live in caves that have closely related ancestors that live outside of caves. Oh, okay, And so you can compare you know, essentially these like sister species or sibling species and see how they differ. And the species that live in caves don't have shorter lives, and in a lot of cases they have longer lives than their surface living counterparts. Well, okay, and then let me tell you about their circadian rhythms. That's the important piece here. So people were trying to figure out if cavefish have circadian rhythms, and they were trying to figure out, like, okay, in the absence of light, how do you do that? And so one idea they had was that maybe bats that go in and out of the cave are what they're queuing into. Because when the bats leave where they come back, they poop in the water and that poop provides food for a lot of cavefish, right, so maybe that's what they're sinking to, but there was no evidence that that was actually happening, So it looks like they're not sinking to that.

00:32:00
Speaker 1: But there could be a lot of similar effects right where things are happening outside the cave, and like even the microbes in the air or something like that could be affecting. You could be sensing indirectly the fact that there's day and night outside the cave from inside the cave.

00:32:14
Speaker 2: Yeah, that's right. But so people have also brought the cavefish into the lab, and when they bring them into the lab and they expose them to normal light cycles, they can develop circadian rhythms. So they still even though they don't have eyes, they still must have like the cells needed to detect light, and they can develop rhythms. But it looks like various parts of their circadian clock are messed up. So if you look at things from the genetic level, it's kind of messed up, and it looks like they also for the most part, are losing their circadian rhythms in the cave, but that doesn't seem to be shortening their lives.

00:32:49
Speaker 1: Wow, fascinating, Yeah, which.

00:32:51
Speaker 2: Is not what I expected. Like I spent a long time being like, well, no, what is the queue? They have to have circadian rhythms, And then I found a review paper that pretty much was like, the rhythms kind of seem to disappear in caves. They're just kind of like moving around whenever and sleeping whenever.

00:33:05
Speaker 1: And that's okay, And that's okay.

00:33:07
Speaker 2: We're not judging.

00:33:08
Speaker 1: Teenagers everywhere are like see mom, it's fine for me to stay up until two.

00:33:11
Speaker 2: Am, all right, and their rooms are kind of like messy caves. And I see lots lots of points of comparison here.

00:33:20
Speaker 1: All right, what about at the bottom of the ocean where light doesn't filter down?

00:33:24
Speaker 2: Okay, so this is interesting. So after I had finished the research on caves, my expectation was that animals that live in the deep sea are also going to not really show circadian rhythms because they're you know, they're down in an area where the light isn't getting to But I thought, well, you know, maybe there's still some cues, Like a lot of the food that comes to the deep sea comes from things just sort of like dying and raining down, and I thought, maybe there's like a daily pattern to how the food rains down. But this is actually really hard to study.

00:33:54
Speaker 1: When the carcass snacks happen, that's really.

00:33:56
Speaker 2: Well, you know, I pay attention to snacks.

00:34:01
Speaker 1: Kids, dead bodies are falling, come on outside. What is it like to be a parent at the bottom of the ocean.

00:34:07
Speaker 2: I mean, when a whale falls down, it is like buffet for months. The videos are messed up. But so the way that folks tend to study this is, you know, they either take the deep sea animals into the lab, but if you bring them into the lab, you're often like turning on lights to study them, and so now they're in like a not natural environment. And you know, labs in general are not like the bottom of the sea. But another way that people study it is they will put like essentially mobile labs. They'll lower them down to the bottom of the sea and then they'll like take pictures or videos and try to see if they can detect cycles and what's happening down there. But another problem there is that they turn on lights often when they do that. Yeah, and so this stuff is hard to study. But I found a study that did use cameras with lights, and they found that a lot of species didn't show detectable patterns, but it was also hard to get large sample sizes. But they did find that there is a kind of worm that lives in a tube and there's a pattern to when it sticks its head out of the tube to try to get food. They were looking at different things that were changing in the environment, and it looks like this behavior is correlated with the tides. So you can still feel the tides at the bottom of the sea. Oh wow, which is amazing. I didn't realize that.

00:35:22
Speaker 1: Yeah, thank you Moon, and see it's all connected. Yes, it turns out there is a through line for the whole episode.

00:35:28
Speaker 5: That's orry.

00:35:28
Speaker 2: I guess. Spaghetification is kind of interesting, but I guess so it's not just the tides, but the tides have different temperatures, so it could be temperature that's queueing this.

00:35:37
Speaker 3: Yea.

00:35:37
Speaker 2: The tides also can bring food, so maybe it's the food that's queuing the clocks. And this information is largely observational, so there's still a lot that we have left to learn, but some indication that tides can be what's impacting timing in the deep sea and that's literally everything I know about circadian clocks, because this is complicated.

00:35:57
Speaker 1: All right, So bottom line for us, what do we know about how circadie rhythms work? And animals that never see the sun.

00:36:02
Speaker 2: Sometimes you're poned and you can't create a circadian rhythm because you just don't have the cues. Other times you can find something that correlates with the light, or sometimes instead of having a circadian rhythm, you have a circ a title rhythm or something, and you're queuing in on some other environmental thing that can help you maintain a rhythm in your life.

00:36:24
Speaker 1: Well, I thought that answer was super colent, fragilistic. But let's hear what our listener says and see if there are follow up questions.

00:36:31
Speaker 5: Wow, thanks for answering my question. Never would have thought that deep sea creatures could sense the tides all the way down there. That's pretty cool.

00:36:59
Speaker 2: We are backed Jupiter, a fascinating planet that could kill us all. Arthur, what do you want to know about Jupiter?

00:37:08
Speaker 6: Hi, Denim and Kelly. Nice to talk to you guys. I have a rocket thrust issue.

00:37:14
Speaker 3: I know that we can't escape the gravity of a black hole no matter how powerful our rocket is, but I don't know the largest mass of a planet we can escape from with our current technology.

00:37:27
Speaker 6: I mean, can an.

00:37:29
Speaker 3: Average space rocket lift off from jupter, from the Sun, from a neutron star?

00:37:34
Speaker 6: I hope you have some funds are in this thanks.

00:37:37
Speaker 1: See, Jupiter is just so attractive gravitationally, people can't stop thinking about it.

00:37:42
Speaker 2: It's beautiful also, all right.

00:37:47
Speaker 1: So Arthur is wondering about taking off from planets because the more massive the planet, the stronger the gravity, the harder it is to lift off of. And he wants to know if an average rocket could actually get you off of Jupiter or even more exotic and denser locations.

00:38:03
Speaker 2: So the first thing I want to know is I can tell from the answer it's going to require math. Did you do these calculations or is there a website that has this information.

00:38:13
Speaker 1: There are a lot of websites that have this information, but I never trust them because you can find mistakes on those websites, which is the source of a lot of mistakes in like chat GBT, because it just like strips some from the websites and gives you the answer, sometimes in the wrong context or whatever. So I always double check these myself. All right, wow, so what matters for lifting off the surface? You're probably going to think escape velocity. And first I want to say it's not about escape velocity, but then it's going to turn out to be about escape.

00:38:41
Speaker 2: Velocity physicists, I know.

00:38:43
Speaker 1: So escape velocity famously is the speed you have to be going so you can escape the gravitational pull of an object. Right, So for example, if I'm standing on the surface of the Earth, how fast do I have to throw a baseball straight up so that it just keeps going forever? That it's kinetic energy over comes the potential energy, Well, that has to climb out of right, So as you move up away from the Earth, you're gaining. Potential energy has to come from somewhere. It comes from your kinetic energy. If you have enough kinetic energy, then you can go forever. Essentially, if your kinetic energy overcomes the potential, well you have to climb. So you have to go fast to escape the Earth. But the reason that's not what this is about is that that's not how rockets work. Right, Rockets you don't slingshot them from the Earth in one push. I mean, people are working on that, and it's hilarious, but traditional rockets.

00:39:32
Speaker 2: Wait, why is it hilarious and not inspirational?

00:39:36
Speaker 1: It's just like the grown up version of a nine year old boy's idea for how to get to space, you know, like, let's pull back a really big rubber band, you know. I mean, I knew they're working on sentrifusions and it's pretty cool, but it seems like impractical to me. Also because the g forces are insane, so I think you could probably launch like stuff into space, but not people.

00:39:56
Speaker 2: Anyway, that's my sense too. Yeah, you're launching stuff hard and.

00:39:59
Speaker 1: Payloads anyway, That's not how traditional rockets work. If you notice, when a rocket takes off, it's not going super duper fast. It's very slowly climbing, right, And that's because rockets don't have a single hard push at the beginning where they gain a lot of speed and then gradually lose it as they rise. They have a continual force. They have an engine on them, so rockets only have to go non zero velocity in order to move up. Right, as long as the force from the rocket is greater than the force of gravity from the Earth, it's going to be moving up okay, right, So it can move up super duper slowly. It could take like a year to take off from the planet, doesn't matter. It's not about escape velocity. It's about putting enough energy in to overcome the potential energy to the Earth, but doesn't have to all be upfront. So that's why it's sort of not about escape velocity.

00:40:46
Speaker 2: Okay. But so say you were lifting off at like a foot per second, that would be much more energetically expensive, wouldn't it, Because you're needing to like maintain the mass you're trying to send up as you slowly go up, And if you do it all faster, that's probably more efficient.

00:41:04
Speaker 1: It's more efficient. Yeah, And if you do it all at once, just by giving it one big push, then you don't need to bring any propellant with you and you can just accelerate the payload. Right Whereas if you're climbing up at a foot per second, yeah, you've got to bring the rest of the latter with you essentially, and you've got to lift that fuel. So we're definitely going to.

00:41:20
Speaker 2: Get there, okay.

00:41:21
Speaker 1: So what we do need to do is think about how much fuel we have to bring and how we can overcome this energy, and so you have to calculate how much kinetic energy do you need to overcome the potential energy the Earth. It's not important that it albeit at once, and rockets do it gradually. But the way to calculate that is to calculate what they call the delta V, the change in velocity that a rocket can provide. And in the end, this turns out to be very similar to the escape velocity, and it makes sense that it's similar because they're both connected to essentially how much energy you need to climb out of this gravitational well and so. On Earth, the escape velocity is about eight kilometers per second. That's how fast you would have to throw a baseball or launch a payload from the surface. But it's also very closely connected. We'll use the rocket equation in a minute to how much fuel you have to bring with you, and that's going to turn out to be the limiting factor of whether you can lift off the planet is can you practically bring enough fuel to get this much delta V? So on Earth you need like eight kilometers per second, and then you go to the rocket equation. The rocket equation says how much mass do you need to bring so that you can do this, so you can climb out of this gravitational well, because remember a rocket, what is it doing. It's throwing stuff out the back. Right. The way it works is it's conserving momentum. Imagine you like in a rowboat and you have a pile of bricks. You throw the bricks out the back of the rowboat. The bricks go backwards, you go forwards. That's how a rocket works. It's throwing stuff out the back. So you have to have that stuff in the rocket to throw out the back in order to propel it. It's helpful if that stuff also has the energy you can use to push the propellant. It doesn't have to be you can have those things be uncoupled. But in a chemical rocket you have fuel which is both propellant and the source of energy, and the rocket equation tells you what your mass ratio is. So on Earth, for example, you need a delta vive about ten kilometers per second. That tells you your mass ratio is nine, which means you need a nine to one fuel to payload mass ratio.

00:43:20
Speaker 2: That's not great.

00:43:21
Speaker 1: It's not great. Yeah, if you have like one hundred kilogram person and a thousand kilogram spaceship around them. You need nine times as much mass in fuel to get that thing into orbit.

00:43:32
Speaker 2: Wow. Yeah, how much worse is it for Jupiter? And does it scale linearly?

00:43:36
Speaker 1: It scales exponentially, which is the bad news. Right, And so say you're on a super Earth which has the mass of like five to ten times the Earth, then the escape velocity is like twenty five to thirty kilometers per second. Okay, that's not so bad. It's three to four times as much, but the mass ratio is ninety three. It's ten times as bad as it is here on Earth.

00:43:57
Speaker 2: Ninety three to one, ninety three to one.

00:44:01
Speaker 1: So instead of having a nine to one fuel to payload ratio, you have a ninety three to one fuel to payload ratio. So now like your rocket is basically just fuel, right, and that's just for a super Earth. Now go to Jupiter. Jupiter is so massive that it's escape velocity is like forty kilometers per second, and this gives a mass ratio of more than one thousand Wow. Right, so you'd need a fuel tank that's a thousand times bigger than your payload. This is probably even an underestimate, but essentially this is impossible for chemistry, right, The chemical rockets cannot achieve this. And if you went to the Sun, right, then the escape velocity from the Sun is four hundred kilometers per second, and so now the mass ratios are just astronomical. From a neutron star, the escape velocity is four tenths the speed of light. And so I couldn't even get my calculator to give me a number on this. W was just so big. And so the bottom line is that chemical rockets, where you have this fuel and you're slowly climbing out of the gravitational well, well they work pretty well if the escape velocity is low. Because the mass ratio is pretty small, you can afford nine to one, which sounded bad already to you, right, But on a bigger planet like a super Earth, it's pretty hard to use. And a Jupiter or the Sun or a neutron star, it's definitely not practical.

00:45:17
Speaker 2: So what about like a project orion's style propulsion system? So if you were exploding nuclear bombs out the back of your rocket to send you up, could you get off of Jupiter?

00:45:28
Speaker 1: Yeah? You could. This is limited to chemical rockets, right, and you can have other strategies you could build a space elevator, right. You could have nuclear propulsion, absolutely, and especially if you're launching the nuclear weapons behind the rocket somehow so that they don't have to come along with the rocket, then you can escape this trap of having to bring all of your propellant with you. Yeah. Or if you have like a light sale with a laser behind it, you can use that to lift off of a planet. Or you could just build your thing in space. Anyway, while you're building it on the surface of Jupiter. Doesn't really make sense unless that's where your super villain hideout is. Oh, which case, I have to wonder Jupiter doesn't get a whole lot of light. I wonder how your circadian rhythms are going in your supervillain layer one.

00:46:11
Speaker 2: You better hope that Bread isn't sending the Earth greening into your your supervillain layer on Jupiter.

00:46:16
Speaker 1: Oh, maybe he's saving us, right, maybe he's using the Earth that doesn't really work, using the Earth to crush somebody else's supervillain layer.

00:46:24
Speaker 5: Yeah, not a.

00:46:25
Speaker 2: Great plan, Brad, not paying you to write that plot, Daniel.

00:46:31
Speaker 1: So yeah, chemical rockets work essentially only on smaller planets. On bigger planets, you need other technologies, but those technologies are not impossible. So I think if we did evolve on Jupiter or on the surface of a neutron star, technically it's still possible to get off of those, but not with rockets.

00:46:48
Speaker 2: All right, let's see if Arthur has any follow up questions, and maybe he'll tell us what his supervillain plan is.

00:46:56
Speaker 6: Thanks guys for the kind of answer my question. I knew that enough from a bigger planet would be hard, but I didn't knoww it would be almost impossible, at least for chemical rockets, as you explained. I think that this either puts a big as the risk on plans for space exploration since the range of celestial bodies we could visit would be very limited, or either forces research for more efficient technologies. As you mentioned, all I have to say about supervillains is that they love rockets these days, so I do not doubt they have plans for this massive loudness.

00:47:33
Speaker 1: Thanks a lot, all right, thank you everybody for sending in your questions. Remember you can write to us two questions at Daniel and Kelly dot org and send us your thoughts about the universe, your musings, your wonderings, your philosophical meanderings. Please, we'd love to hear from you.

00:47:46
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00:47:47
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