WEBVTT - Did the Earth ever have a ring? 0:00:06.080 --> 0:00:08.200 The message you often hear about space is that it's 0:00:08.280 --> 0:00:11.119 vast and empty. The Earth and even the Sun are 0:00:11.160 --> 0:00:14.600 these tiny dots and a huge ocean of black space. 0:00:15.000 --> 0:00:17.280 That's all true, but it gives you the wrong idea 0:00:17.360 --> 0:00:21.479 about our cosmic neighborhood. It suggests that the Earth is isolated, alone, 0:00:21.840 --> 0:00:25.560 not affected by our neighbors, not in danger. The truth 0:00:25.640 --> 0:00:29.400 is actually the opposite. Space is vast, but gravity is 0:00:29.440 --> 0:00:32.760 also very patient. There are a lot of big dark 0:00:32.880 --> 0:00:35.919 rocks out there that could get tugged by gravity towards 0:00:35.920 --> 0:00:39.040 the Earth and then dramatically affect our way of life, 0:00:39.240 --> 0:00:42.760 both positively or negatively. They could, of course smash into 0:00:42.840 --> 0:00:45.240 us and cause an extinction event, but then they could 0:00:45.320 --> 0:00:50.040 also create new snazzy bling around our planet. So today 0:00:50.080 --> 0:00:52.240 we're going to dig deep into the history of Earth 0:00:52.280 --> 0:00:56.360 within our cosmic neighborhood, understand the gravitational dance between all 0:00:56.400 --> 0:00:58.959 of these objects, and ask the question about whether there 0:00:59.000 --> 0:01:01.920 was ever a time when the universe put a ring 0:01:02.160 --> 0:01:05.679 on the Earth. So, just in time for Valentine's Day, 0:01:05.680 --> 0:01:10.080 we're getting cosmically romantic and asking did Earth ever have 0:01:10.200 --> 0:01:28.600 a ring? Welcome to Daniel and Kelly's extraordinary universe. Hello. 0:01:28.800 --> 0:01:32.200 I'm Kelly Wienersmith. I'm a parasitologist and I stopped wearing 0:01:32.280 --> 0:01:35.520 rings because I got fish guts stuck in my ring 0:01:35.720 --> 0:01:38.440 too many times and decided it was too gross. 0:01:39.600 --> 0:01:41.440 Oh isn't that romantic though? 0:01:42.200 --> 0:01:45.200 Fish guts in a ring? You got a weird sense 0:01:45.240 --> 0:01:48.240 of romance, Daniel, I'm. 0:01:48.120 --> 0:01:51.920 Trying to resonate with a biology. Hi. I'm Daniel. I'm 0:01:51.960 --> 0:01:55.280 a particle physicist, and I bought my wedding rings for 0:01:55.360 --> 0:01:57.880 two dollars on Telegraph Avenue in Berkeley. 0:01:58.480 --> 0:02:01.440 I was going to ask you, are you and Katrina 0:02:01.520 --> 0:02:03.000 ring people or not ring people? 0:02:03.240 --> 0:02:05.840 We have rings which we feel sentimental about, but we're 0:02:05.880 --> 0:02:08.520 not people who are into expensive fancy stuff. So like 0:02:08.919 --> 0:02:11.360 her engagement ring has a piece of amber in it, 0:02:11.360 --> 0:02:13.960 and I designed the ring myself. There's no like crazy 0:02:14.000 --> 0:02:16.200 diamond in there. And we didn't want to spend a 0:02:16.200 --> 0:02:18.600 lot of money on crazy rings, so we just walked 0:02:18.600 --> 0:02:21.240 down Telegraph Avenue and found a guy who made silver 0:02:21.360 --> 0:02:23.679 rings and bottom for a couple of bucks. 0:02:24.040 --> 0:02:26.360 You designed a ring with amber and got it for 0:02:26.400 --> 0:02:26.919 two bucks. 0:02:27.040 --> 0:02:29.600 Oh no, the engagement ring I had a friend make, 0:02:29.919 --> 0:02:32.080 so that was more than two dollars, but yes, I 0:02:32.160 --> 0:02:34.760 designed it myself. It has a bunch of Danish ruins 0:02:34.840 --> 0:02:36.919 in it and stuff and a piece of amber in 0:02:36.960 --> 0:02:37.359 the middle. 0:02:37.560 --> 0:02:38.400 Oh that's great. 0:02:38.760 --> 0:02:40.360 How about you? What's your guys ring story? 0:02:40.480 --> 0:02:42.600 Can I tell you our engagement story really quick? Oh? 0:02:42.680 --> 0:02:44.560 Yes? Does it involve fish cuts? No? 0:02:44.560 --> 0:02:46.720 No, the rest of our life involves fish cuts, but no, 0:02:46.840 --> 0:02:49.400 our engagement story. So Zach is like not a super 0:02:49.480 --> 0:02:52.520 sentimental guy, and so, like, a couple months earlier, I 0:02:52.520 --> 0:02:54.280 had said to him, like, hey, you know we've been 0:02:54.280 --> 0:02:56.640 together for a year, do you think you could ever 0:02:57.480 --> 0:02:59.880 see yourself marrying me? Because if still, let's keep going. 0:02:59.880 --> 0:03:02.200 But if not, let's like cut our losses and bee 0:03:02.360 --> 0:03:05.160 like this was fun. And so his response, and this 0:03:05.240 --> 0:03:09.560 is amazing. His response was I think you're really nice, wow, 0:03:09.840 --> 0:03:12.799 which I thought was him being like I don't want 0:03:12.800 --> 0:03:15.200 to answer this question because it's going to be uncomfortable, 0:03:15.200 --> 0:03:17.240 but like, that's not what I was looking for, right, 0:03:17.280 --> 0:03:19.320 And so I thought to myself, like, Okay, in a 0:03:19.360 --> 0:03:21.959 couple more months, I'm going to ask him this again, 0:03:22.080 --> 0:03:23.760 and if I don't get a better answer, it's over. 0:03:24.560 --> 0:03:27.160 But so Zach thought, well, you marry the person who 0:03:27.120 --> 0:03:29.560 you think is really nice. So he thought he had 0:03:29.600 --> 0:03:31.440 said like, yeah, I could marry you one day, and 0:03:31.480 --> 0:03:33.600 he thought after that conversation that it was locked in 0:03:33.880 --> 0:03:35.720 and that he didn't even really need to ask. 0:03:35.800 --> 0:03:37.680 That was like the most positive thing he could think 0:03:37.720 --> 0:03:39.680 of saying, I think you're really nice. 0:03:40.320 --> 0:03:43.840 No, he's not a super sentimental side. So it was 0:03:43.920 --> 0:03:46.680 Pie Day, March fourteenth, and he gave me a little 0:03:46.680 --> 0:03:48.800 card with a pie on it that said don't open 0:03:48.880 --> 0:03:51.520 until what are the extended digits of pie? So three 0:03:51.600 --> 0:03:54.680 fourteen is the date, and then it's nine okay, yeah, 0:03:54.680 --> 0:03:57.240 so don't open until one fifty nine. And I thought 0:03:57.240 --> 0:03:58.840 it was going to be a poem about how like 0:03:58.880 --> 0:04:01.880 I eat too much pie he writes like weird poems, 0:04:02.160 --> 0:04:05.000 and I forgot about it, and so later in the day, 0:04:05.200 --> 0:04:07.000 it was like four pm and he was in the 0:04:07.080 --> 0:04:09.400 restroom and I reached into my pocket and I was like, oh, 0:04:09.440 --> 0:04:11.880 I've got this card in my pocket and it's after 0:04:11.880 --> 0:04:13.680 one fifty nine, so I can open it. And it 0:04:13.760 --> 0:04:16.600 said something to the effect of, like, you get frustrated 0:04:16.600 --> 0:04:18.799 because I forgot our anniversary. But if we got engaged 0:04:18.800 --> 0:04:20.719 on Pie Day, that's a date I'd always remember. 0:04:20.800 --> 0:04:21.680 Oh my gosh. 0:04:21.760 --> 0:04:23.760 And so he came out of the bathroom and I 0:04:23.839 --> 0:04:26.039 was like, are you asking me to marry you? And 0:04:26.080 --> 0:04:29.240 so I'll note that he forgot when one fifty nine passed, 0:04:29.240 --> 0:04:31.400 so he wasn't worried about the answer. He knew what 0:04:31.440 --> 0:04:32.400 the answer was gonna be. 0:04:32.600 --> 0:04:34.320 And I love that there's a bathroom visit in the 0:04:34.320 --> 0:04:36.839 middle of this story. That's very Kelly and Zach. 0:04:38.400 --> 0:04:41.400 Exactly, very scatological. And so I was like, wait, so 0:04:41.480 --> 0:04:43.840 are we engaged now? And all he said was, well, 0:04:43.839 --> 0:04:45.279 you weren't supposed to read it while I was on 0:04:45.320 --> 0:04:51.280 the hut. Anyway, he didn't have a ring, he didn't 0:04:51.320 --> 0:04:54.200 have anything. We're not very sentimental. So anyway, we went out. 0:04:54.200 --> 0:04:56.359 We got a ring. I got fish guts in it, 0:04:56.400 --> 0:04:58.640 so I stopped wearing it because while I was doing dissections, 0:04:58.680 --> 0:05:00.640 it kept getting in the way. I got him a ring, 0:05:01.200 --> 0:05:03.920 and when we were walking around Rice University, our daughter 0:05:04.000 --> 0:05:05.960 was playing with it, and I was like, Zach, and 0:05:06.000 --> 0:05:08.560 she was like two as like, Zach, she's gonna drop it. 0:05:08.640 --> 0:05:11.320 You're gonna lose your wedding ring. You probably shouldn't let 0:05:11.360 --> 0:05:12.919 her play with it. And we got back into the 0:05:12.960 --> 0:05:17.160 car and he sat down and he goes, uh oh. 0:05:17.200 --> 0:05:19.680 And anyway, so he lost his ring, and I don't 0:05:19.720 --> 0:05:22.200 wear mine because of fish guts and we are not 0:05:22.360 --> 0:05:25.000 super sentimental. But you know, it's been almost twenty years 0:05:25.000 --> 0:05:27.080 since we've been together, so it's working out. 0:05:27.360 --> 0:05:30.720 So Zach's ring is somewhere on the campus of Rice University, or. 0:05:31.160 --> 0:05:34.560 Some undergrad plays drinking games with it or something. I 0:05:34.560 --> 0:05:36.479 don't know. I don't know where it ended up. We 0:05:36.600 --> 0:05:37.320 never found it. 0:05:37.440 --> 0:05:39.680 All right, Rice students, if you see a ring on campus, 0:05:39.880 --> 0:05:40.960 send it to Kelly. 0:05:41.920 --> 0:05:44.080 Yeah, I'll take all the random rings that get lost 0:05:44.120 --> 0:05:47.159 on campus. All right, Well, I've gotten us off topic. 0:05:47.279 --> 0:05:50.000 Your story was lovely. Mine was hopefully good for a laugh. 0:05:50.279 --> 0:05:53.240 But today we're talking about whether or not Earth ever 0:05:53.360 --> 0:05:55.919 had a ring, which is a fun question to think about. 0:05:56.120 --> 0:05:58.560 It's fun to think about because it makes us think 0:05:58.600 --> 0:06:01.640 about the deep past and how we think of the 0:06:01.680 --> 0:06:04.120 Earth as a certain way and having the moon and 0:06:04.480 --> 0:06:06.840 the sky looks a certain way and the solar systems 0:06:06.920 --> 0:06:09.320 arranged a certain way, and we imagine it's always been 0:06:09.360 --> 0:06:12.760 that way or forzillions of years. But it turns out 0:06:12.800 --> 0:06:15.680 that on a cosmic time scale, the solar system has 0:06:15.720 --> 0:06:18.920 a very chaotic history, and things used to look quite 0:06:18.920 --> 0:06:21.200 a bit different. So it's really fun for me to 0:06:21.839 --> 0:06:24.479 go deep into the past and learn about how the 0:06:24.520 --> 0:06:27.000 Solar system used to be quite different, how life on 0:06:27.040 --> 0:06:28.880 Earth could have been different. You could have looked up 0:06:28.880 --> 0:06:31.320 at the sky and seeing different stuff out there. 0:06:31.440 --> 0:06:32.719 And I got to say, when you sent me this 0:06:32.839 --> 0:06:36.320 idea for a podcast episode topic, it had not been 0:06:36.360 --> 0:06:38.680 on my radar at all that Earth could have ever 0:06:38.760 --> 0:06:41.440 had a ring. So I'm excited about hearing the answer 0:06:41.480 --> 0:06:41.720 to this. 0:06:42.960 --> 0:06:45.200 So I was wondering if folks out there had considered 0:06:45.200 --> 0:06:48.000 the possibility of whether Earth had ever had a ring. 0:06:48.279 --> 0:06:50.640 So I sent this question to our intrepid volunteers. Thank 0:06:50.640 --> 0:06:53.159 you very much to everybody who plays along. If you 0:06:53.200 --> 0:06:56.360 would like to hear your voice answering questions on the podcast, 0:06:56.560 --> 0:06:58.680 please don't be shy. We would love to have you 0:06:58.960 --> 0:07:01.560 as part of the chorus. To us two questions at 0:07:01.680 --> 0:07:04.880 Danielankelly dot org and we will set you up in 0:07:04.920 --> 0:07:06.880 the meantime. Think about it for a minute. Do you 0:07:06.920 --> 0:07:10.600 think Earth could have ever had a ring? Here's what 0:07:10.680 --> 0:07:15.040 our listeners had to say. A big meteorite smashed into 0:07:15.080 --> 0:07:19.280 the Earth all the debris shot up into the into space. 0:07:19.600 --> 0:07:22.360 The Earth did have a ring with the material that 0:07:22.520 --> 0:07:24.040 eventually call us into the Moon. 0:07:24.200 --> 0:07:26.440 Yes, it did have a ring, and it still does. 0:07:27.120 --> 0:07:30.960 Maybe it did, like with all the rocks flying around 0:07:31.000 --> 0:07:34.120 it right at the beginning when it was being formed, 0:07:34.560 --> 0:07:40.080 had like a wriggled rocks around it. And maybe when 0:07:40.400 --> 0:07:44.520 the ice it happens and been a thing of vice 0:07:44.600 --> 0:07:47.560 around it when there was the ice. Say, I don't 0:07:47.600 --> 0:07:49.160 really think that could have happened. 0:07:49.800 --> 0:07:51.960 So, yes, the Earth probably had a ring when the 0:07:52.000 --> 0:07:55.000 Moon was born. As bodies coal started to fall into 0:07:55.000 --> 0:07:57.160 planet olids and eventually planets that would have been rings. 0:07:57.280 --> 0:07:59.920 Earth might have had a ring after the collision with Theata. 0:08:00.160 --> 0:08:03.120 If you're referring to a persistent ring system akin to Saturns, 0:08:03.240 --> 0:08:05.560 then that's more of a complex question open to interpretation. 0:08:06.080 --> 0:08:10.080 The ejecta from that collision temporarily formed a ring. 0:08:10.240 --> 0:08:12.840 There is a chance that's to be some sort of 0:08:12.880 --> 0:08:14.400 ring during its creation. 0:08:15.080 --> 0:08:18.800 It no longer has a ring because it is divorced. 0:08:19.440 --> 0:08:21.680 Middle Earth did and it was a big freaking deal. 0:08:22.240 --> 0:08:25.240 Is that one of the theories or hypotheses behind where 0:08:25.240 --> 0:08:26.640 the Moon came from. 0:08:26.280 --> 0:08:31.800 When a Mars sized object collided with Earth. Do Bear's 0:08:31.800 --> 0:08:32.520 poop in the woods? 0:08:33.200 --> 0:08:35.000 Do taco taste better on Tuesdays? 0:08:35.160 --> 0:08:37.040 Does Tom Cruise will have to sprint like a maniac 0:08:37.080 --> 0:08:39.959 in every one of his movies? Yes, yes, the Earth 0:08:40.040 --> 0:08:41.400 had a ring, but. 0:08:41.320 --> 0:08:44.320 I'll do notize that Liberachi had rings during the formation 0:08:44.360 --> 0:08:44.840 of the Moon. 0:08:45.640 --> 0:08:48.600 No, I mean Saturn offered, but long distance relationships just 0:08:48.640 --> 0:08:49.200 never work out. 0:08:49.840 --> 0:08:52.720 And a protope planet hits it to form the Moon. 0:08:52.800 --> 0:08:55.280 While the moon was being formed. 0:08:56.360 --> 0:08:58.400 I really don't know, but I imagine not since the 0:08:58.440 --> 0:08:59.560 moon has been there. 0:09:00.160 --> 0:09:03.720 That was an amazing mix of like serious good answers 0:09:03.800 --> 0:09:06.520 and some really clever not answers. 0:09:07.480 --> 0:09:10.120 I think Tom Cruise does sprint in every movie he's in. 0:09:10.240 --> 0:09:12.640 I think that's true every. 0:09:12.520 --> 0:09:14.920 Movie I can think of. Did he sprint in Jerry Maguire, 0:09:16.400 --> 0:09:18.240 He must have. There must have been a reason to sprint. 0:09:18.360 --> 0:09:20.640 Somebody check the footage, Okay, let us know. 0:09:20.960 --> 0:09:22.400 And I was a little surprised, though I guess I 0:09:22.400 --> 0:09:24.880 shouldn't have been that most people went to the sort 0:09:24.920 --> 0:09:28.680 of early formation of the Earth, the impact with the 0:09:28.720 --> 0:09:31.760 protoplanet that formed the Moon, and thinking about how that 0:09:31.880 --> 0:09:33.840 might have been a ring as well, and that's a 0:09:33.960 --> 0:09:36.920 totally reasonable answer. That it's not what I was going 0:09:36.960 --> 0:09:38.559 for for today's episode. 0:09:38.720 --> 0:09:41.840 Well, I think probably it would help to know how 0:09:41.960 --> 0:09:44.200 rings are formed in general. So I'm guessing you're going 0:09:44.240 --> 0:09:48.680 to tell us that today, but let's start even earlier. So, like, 0:09:48.760 --> 0:09:50.920 what are rings? I guess I realized, Well, I was 0:09:50.920 --> 0:09:53.520 thinking about this question, like, you know, the moon orbits 0:09:53.520 --> 0:09:56.000 in a ring, but that's not a ring. How continuous 0:09:56.040 --> 0:09:57.960 does the line need to be before you have a 0:09:58.000 --> 0:09:59.160 satellite versus a ring? 0:09:59.280 --> 0:10:03.000 Yeah, so it's astronomy, which means we're going to do 0:10:03.040 --> 0:10:06.800 our best to draw arbitrary dotted lines between the continuous 0:10:06.840 --> 0:10:10.679 concepts that really exist on a spectrum. But you know, 0:10:10.720 --> 0:10:12.760 some things we call moons, some things we call rings. 0:10:12.800 --> 0:10:15.400 What's the difference? How many tiny moons does it take 0:10:15.400 --> 0:10:18.080 before you start calling it a ring? Typically we call 0:10:18.160 --> 0:10:22.040 something a ring if it's composed of solid materials such 0:10:22.040 --> 0:10:26.480 as dust or moonlits, But it's not in one single object. 0:10:26.760 --> 0:10:30.080 So you know, basically there's a spectrum between Like you 0:10:30.120 --> 0:10:32.520 have one single object, you call that a moon. If 0:10:32.559 --> 0:10:35.200 you break that moon up into little rocks, you could 0:10:35.240 --> 0:10:38.360 call those moonlits, Or you could say if they're fine 0:10:38.440 --> 0:10:39.760 enough you could call it a ring. 0:10:40.040 --> 0:10:42.320 But if you had two objects as big as the 0:10:42.320 --> 0:10:45.080 Moon that somehow didn't run into each other, would that 0:10:45.120 --> 0:10:47.679 be a ring. Does Mars have a ring or does 0:10:47.679 --> 0:10:48.680 it just have two moons? 0:10:48.880 --> 0:10:52.480 Mars has two moons, so I think there isn't a 0:10:52.600 --> 0:10:56.559 very crisp distinction. I couldn't find a crisp distinction online. 0:10:56.600 --> 0:10:58.800 I don't think like the astronomers have had a meeting 0:10:59.360 --> 0:11:00.560 arguing about this yet. 0:11:00.720 --> 0:11:03.600 Nature doesn't care about our criteria in our categories. 0:11:04.000 --> 0:11:06.000 But I think one thing that is important for a 0:11:06.080 --> 0:11:10.000 ring is that it's basically in a plane. So, you know, 0:11:10.080 --> 0:11:13.440 a swarm of objects surrounding a planet, you wouldn't call 0:11:13.480 --> 0:11:15.320 that a ring. If it's like in a sphere. If 0:11:15.320 --> 0:11:18.600 it's orbiting in every direction and completely surrounding the planet 0:11:18.600 --> 0:11:21.440 with little rocks, that isn't a ring. When distinguishing feature 0:11:21.480 --> 0:11:24.800 of a ring is that it does orbit in a plane, right, that, like, 0:11:24.840 --> 0:11:28.280 the vertical motion relative to the ring is small compared 0:11:28.280 --> 0:11:30.040 to the motion around the planet. 0:11:30.240 --> 0:11:34.079 Does it happen that you get junk like all around 0:11:34.120 --> 0:11:36.160 a planet or does it always end up in the 0:11:36.200 --> 0:11:37.360 same plane as a ring? 0:11:37.720 --> 0:11:41.000 Yeah? Great question. You can get junk around a planet, 0:11:41.360 --> 0:11:43.800 but that's sort of temporary. That's not a very stable 0:11:43.840 --> 0:11:47.440 situation because gravity will eventually pull it down together into 0:11:47.440 --> 0:11:50.920 a plane. There's a reason that planets have rings and 0:11:51.000 --> 0:11:53.840 not swarms of stuff. And there's a reason that moons 0:11:53.880 --> 0:11:57.040 typically form in a single plane around a planet, which 0:11:57.080 --> 0:12:00.800 aligns with the planet's spin usually, And it's the same 0:12:00.840 --> 0:12:04.520 reason why the planets all spin in the same plane 0:12:04.720 --> 0:12:08.079 as their motion around the Sun, which aligns with the 0:12:08.240 --> 0:12:11.840 rotation of the Sun. And the reason is angular momentum. 0:12:12.240 --> 0:12:14.920 Gravity would like to pull everything down together into a 0:12:14.960 --> 0:12:18.240 little dot. What resists that, Well, sometimes it's like structural 0:12:18.320 --> 0:12:20.800 or integrity. The Earth doesn't collapse into a black hole 0:12:21.280 --> 0:12:24.400 because it's solid, right, and the rocks resist being crushed. 0:12:24.720 --> 0:12:27.360 But there's another factor there, which is the Earth is spinning, 0:12:27.800 --> 0:12:29.760 and the spinning of the Earth sort of fluffs it 0:12:29.840 --> 0:12:32.400 up a little bit and makes it larger. So like 0:12:32.440 --> 0:12:35.400 the Earth's radius from the core to the surface is 0:12:35.520 --> 0:12:38.320 larger at the equator because it's spinning, and if the 0:12:38.320 --> 0:12:41.160 Earth was softer like pizza dough, it would get flatter 0:12:41.240 --> 0:12:45.360 and flatter as that spinning resists gravity. But the spinning 0:12:45.400 --> 0:12:48.440 only resists gravity along the plane. Right, So if you 0:12:48.480 --> 0:12:52.679 have like the Earth spin axis, the spinning helps resist gravity, 0:12:52.720 --> 0:12:56.560 helps keep Earth fluffed out along the plane of that 0:12:56.720 --> 0:13:00.319 spin right, so the axis is perpendicular to the plane, 0:13:00.520 --> 0:13:02.960 but it doesn't prevent things from collapsing to the plane. 0:13:03.400 --> 0:13:05.320 So now I imagine you have a big swarm of 0:13:05.360 --> 0:13:08.520 stuff that's swirling around the Earth. Gravity can pull it 0:13:08.559 --> 0:13:11.960 down into that plane, making a disk, but the spinning 0:13:12.040 --> 0:13:15.199 keeps gravity from pulling it down into the Earth necessarily. 0:13:15.600 --> 0:13:18.160 That's why a big swarm of stuff would collapse into 0:13:18.200 --> 0:13:20.840 a plane. And it's the same reason why the whole 0:13:20.880 --> 0:13:25.160 solar system has collapsed into a plane. The original blob 0:13:25.240 --> 0:13:28.559 of gas and dust that formed our solar system collapse 0:13:28.640 --> 0:13:32.080 due to gravity, but didn't collapse as far along that plane. 0:13:32.120 --> 0:13:35.880 Because everything is spinning, it keeps stuff from falling all 0:13:35.920 --> 0:13:36.360 the way in. 0:13:37.000 --> 0:13:42.480 So if you had a speck around the Earth, not 0:13:42.679 --> 0:13:46.200 around like the plane where you get the ring, would 0:13:46.200 --> 0:13:49.079 it get thrown out or pulled in or either? 0:13:49.559 --> 0:13:52.800 Yeah? So say, for example, Earth has a big ring 0:13:53.400 --> 0:13:56.400 and now you add a rock in a random orientation 0:13:56.760 --> 0:13:59.240 to the Earth. What's going to happen to it? Well, 0:13:59.240 --> 0:14:01.520 it has a lot of al so it's not going 0:14:01.520 --> 0:14:03.120 to fall to the Earth. It's going to be an orbit, 0:14:03.360 --> 0:14:05.839 but it's going to get gravitated towards the ring. The 0:14:05.920 --> 0:14:08.000 ring is going to pull it in, and so while 0:14:08.000 --> 0:14:10.440 it's going to maintain an orbit because of its speed, 0:14:10.679 --> 0:14:13.400 that orbit's going to shift until it joins the ring. 0:14:13.559 --> 0:14:15.840 The ring, because of its gravity, is going to pull 0:14:16.040 --> 0:14:18.800 that new rock into it. So gravity pulls things together, 0:14:18.960 --> 0:14:20.920 but it can't overcome angular momentum. 0:14:21.080 --> 0:14:26.560 Okay, And are rings always at the equator of the 0:14:26.600 --> 0:14:28.800 thing that they're orbiting around, And if the thing is 0:14:28.840 --> 0:14:30.760 at a tilt, that's why it doesn't look like it's 0:14:30.760 --> 0:14:34.000 straight around. So like Saturn, is that a tilt and 0:14:34.000 --> 0:14:35.480 that's why it's rings are kind of tilty. 0:14:35.800 --> 0:14:38.240 Yes, great question, And it depends a little bit on 0:14:38.320 --> 0:14:40.840 the formation. And this is actually a question people have 0:14:40.880 --> 0:14:43.960 about how rings form, Like if the ring formed from 0:14:43.960 --> 0:14:47.440 the original blob of stuff that made the planet. And 0:14:47.520 --> 0:14:49.760 one of the theories for how rings formed is you 0:14:49.760 --> 0:14:51.720 have a big blob of stuff and some of it 0:14:51.760 --> 0:14:54.360 collapses into a planet, and some of it doesn't because 0:14:54.360 --> 0:14:56.720 it's moving too fast and it stays outside and forms 0:14:56.720 --> 0:14:59.200 a ring. Then it all comes from the initial blob 0:14:59.240 --> 0:15:01.240 of stuff that's spin, and then you expect it to 0:15:01.280 --> 0:15:04.000 have the same spin on the same plane and basically 0:15:04.000 --> 0:15:06.680 be around the equator of the planet. But another theory 0:15:06.720 --> 0:15:08.640 is that these rings come from the outside. You have 0:15:08.640 --> 0:15:12.120 a planet that forms, it's already spinning and hard and compact, 0:15:12.400 --> 0:15:15.280 and now some material comes from the outside is captured 0:15:15.320 --> 0:15:18.080 by the planet into a ring that will collapse on 0:15:18.160 --> 0:15:20.680 its own, but its axis doesn't have to align with 0:15:20.720 --> 0:15:23.440 the axis of the planet. Gravity will pull it down 0:15:23.880 --> 0:15:26.440 into a single ring and it will orbit around its 0:15:26.480 --> 0:15:29.360 own spin axis. It doesn't have to align with the planet. 0:15:29.400 --> 0:15:32.160 There's nothing the planet can do to change its spin 0:15:32.280 --> 0:15:34.600 axis because angular momentum is conserved. 0:15:34.760 --> 0:15:36.520 All right, Is there anything else we need to know 0:15:36.520 --> 0:15:38.840 about how rings are formed? Are we all now experts? 0:15:40.640 --> 0:15:43.040 Another thing to think about is the difference between the 0:15:43.040 --> 0:15:46.480 formation of moons and rings, Like, why do some planets 0:15:46.480 --> 0:15:48.080 have rings and some of them have moons and some 0:15:48.160 --> 0:15:51.680 of them have both? You know, why doesn't gravity always 0:15:51.760 --> 0:15:54.640 pull a ring together into a moon? Right? You could 0:15:54.680 --> 0:15:59.080 imagine like a string of little moonlits orbiting together in 0:15:59.120 --> 0:16:02.760 a circle r planet. Why doesn't gravity always pull those together. 0:16:03.120 --> 0:16:05.840 It can do that without violating anyngular momentum. And the 0:16:05.880 --> 0:16:09.200 answer there is tidal forces. Usually when we think about 0:16:09.200 --> 0:16:11.960 the Solar System, we're thinking about gravity as just like 0:16:12.040 --> 0:16:13.640 here you have a rock and there you have a rock, 0:16:13.760 --> 0:16:16.000 and there's gravity between them and they're pulling on each other. 0:16:16.400 --> 0:16:18.720 But gravity is a little bit more complex than that. 0:16:19.120 --> 0:16:21.920 If your rocks are not just points objects. If they're 0:16:21.960 --> 0:16:24.160 just points, then you can just think about the gravity 0:16:24.160 --> 0:16:26.920 on the objects. But if it's big, then you have 0:16:27.040 --> 0:16:30.000 one side that's closer and another side that's further, and 0:16:30.080 --> 0:16:33.240 gravity depends on distance. So gravity is going to pull 0:16:33.320 --> 0:16:36.000 on the closer part harder than it's pulling on the 0:16:36.080 --> 0:16:39.640 further part. And that's true always. So for example, if 0:16:39.680 --> 0:16:42.640 you're an astronaut and you're in space and you're doing 0:16:42.920 --> 0:16:45.720 an ev or whatever, the Earth is pulling on your 0:16:45.720 --> 0:16:49.320 feet harder than it's pulling on your head. You might think, 0:16:49.400 --> 0:16:53.280 no big deal, But those are relative forces. You can 0:16:53.320 --> 0:16:55.040 think of it as pulling on your feet harder than 0:16:55.080 --> 0:16:57.840 your head, or equivalently, you can think the Earth is 0:16:57.840 --> 0:16:59.640 trying to pull your head off of your body, because 0:16:59.640 --> 0:17:02.320 that's really what it's doing, right, It's pulling on one 0:17:02.360 --> 0:17:04.640 side harder than the other side. It's trying to tear 0:17:04.680 --> 0:17:07.280 you apart. And normally your neck is strong enough that 0:17:07.280 --> 0:17:09.840 the Earth's not going to decapitate you. But if you 0:17:09.880 --> 0:17:12.840 are close to a very powerful body like a black hole, 0:17:13.000 --> 0:17:15.720 then those tidle forces are powerful enough to pull you apart. 0:17:15.800 --> 0:17:19.760 That's what spaghetification is. And so planets pull on things. 0:17:19.840 --> 0:17:22.240 The Earth, for example, is tugging on the Moon. It's 0:17:22.320 --> 0:17:24.480 trying to squeeze the Moon into a football. It's trying 0:17:24.520 --> 0:17:27.160 to pull rocks off the surface of the Moon that's 0:17:27.200 --> 0:17:27.919 closer to it. 0:17:28.240 --> 0:17:30.840 I can imagine how that pulling over time would start 0:17:30.880 --> 0:17:33.960 to pull off pieces and result in a ring. So 0:17:34.040 --> 0:17:36.000 does that mean that a lot of the rings around 0:17:36.000 --> 0:17:38.720 planets are moons that just got kind of crushed? And 0:17:38.720 --> 0:17:41.359 then why didn't our moon end up succumbing to that? 0:17:41.880 --> 0:17:45.520 Sure, it depends on distance. It also depends on structural 0:17:45.520 --> 0:17:48.040 integrity what your moon is made out of. But basically, 0:17:48.080 --> 0:17:50.080 if a moon gets too close to a planet, the 0:17:50.119 --> 0:17:52.560 tidle forces will pull it apart. If the moon is 0:17:52.600 --> 0:17:55.520 far enough away, then the structural integrity of the moon 0:17:55.760 --> 0:17:58.840 is more powerful than the tidal forces. It'll stay together. 0:17:59.160 --> 0:18:00.480 So if you look at all the planets in the 0:18:00.520 --> 0:18:03.159 Solar System, you notice that it's usually rings on the 0:18:03.160 --> 0:18:06.760 inside and moons on the outside. And you can calculate 0:18:06.840 --> 0:18:09.080 this sort of dividing line. It's called the Roche limit. 0:18:09.480 --> 0:18:11.400 Things that are closer than the roach limit, the tidal 0:18:11.480 --> 0:18:13.720 forces will probably pull it apart. Things that are further 0:18:13.880 --> 0:18:16.600 things will coalesce into a moon. The self gravity will 0:18:16.600 --> 0:18:19.560 pull it together, and then the structural forces will hold it. 0:18:19.640 --> 0:18:22.840 Is it an interplay between distance and size or is 0:18:22.880 --> 0:18:26.880 it just size or distance? Size and what you're made 0:18:26.920 --> 0:18:29.160 out of, like a chunk of metal, would be harder 0:18:29.200 --> 0:18:30.840 to pull apart than something else. 0:18:30.880 --> 0:18:33.360 It's mostly distance from the planet and what you're made 0:18:33.359 --> 0:18:36.320 out of. So, for example, there's a different roach limit 0:18:36.560 --> 0:18:38.800 for a blob of water than there is for like 0:18:38.840 --> 0:18:41.359 a moon made of diamond, which would be much harder 0:18:41.359 --> 0:18:44.000 to pull apart, but for like a typical rock. You 0:18:44.040 --> 0:18:47.360 can calculate these distances. For the moon, for example, if 0:18:47.359 --> 0:18:49.520 it came within ten thousand kilometers of the surface of 0:18:49.560 --> 0:18:52.000 the Earth, it would be pulled apart. Its orbit is 0:18:52.000 --> 0:18:55.240 safely outside that. It's like three hundred and ninety thousand kilometers, 0:18:55.240 --> 0:18:58.080 so it's well past the Roach limit. And you know, 0:18:58.119 --> 0:19:00.280 the Sun has a roach limit. If a planet gets 0:19:00.280 --> 0:19:02.520