WEBVTT - How do planets get their moons? 0:00:08.600 --> 0:00:12.160 Hey, do you ever wish that we had more moons 0:00:12.240 --> 0:00:13.119 in our night sky? 0:00:14.200 --> 0:00:18.320 Hmmm? I think the universe as moon does enough times. 0:00:18.400 --> 0:00:23.560 Actually, well, I like the moons, and I sometimes wish 0:00:23.640 --> 0:00:25.720 we had more going on in the night sky, like 0:00:25.880 --> 0:00:27.080 lots of little moons. 0:00:28.160 --> 0:00:31.120 But then I wonder if we had the same line 0:00:31.120 --> 0:00:33.560 in Star Wars, you know, where he says that's no moon. 0:00:34.040 --> 0:00:34.720 That wouldn't work. 0:00:36.600 --> 0:00:38.559 Maybe instead of the Death Star, they would have had 0:00:38.560 --> 0:00:40.360 the death constellation. 0:00:40.159 --> 0:00:41.960 Or that song when the moon hits your eye like 0:00:42.000 --> 0:00:44.440 a big pizza pie. That wouldn't work with a lot 0:00:44.479 --> 0:00:47.480 of little moons. I guess it would work with lots 0:00:47.479 --> 0:00:48.760 of mini pizzas. 0:00:50.479 --> 0:00:53.000 The personal pan pizza would have been invented earlier. 0:01:08.440 --> 0:01:11.320 Hi am Horehea, ma cartoonist and the creator of PhD comics. 0:01:11.520 --> 0:01:14.679 Hi I'm Daniel. I'm a particle physicist and a professor 0:01:14.800 --> 0:01:17.679 at UC Irvine, and I'd never really been a fan 0:01:17.800 --> 0:01:19.160 of the pan pizza, of. 0:01:19.120 --> 0:01:21.880 The pan or the pizza or just a combination of 0:01:21.920 --> 0:01:22.200 the two. 0:01:22.280 --> 0:01:24.760 The pizza in the pan. Definitely a thin crust kind 0:01:24.800 --> 0:01:26.160 of guy over here, not. 0:01:26.440 --> 0:01:28.800 A bread fan trying to curb your carbs. 0:01:30.080 --> 0:01:31.920 I like tomato sauce. But I don't like the kiddie 0:01:31.920 --> 0:01:34.600 pool of marinera that they call pizza in Chicago. 0:01:34.680 --> 0:01:37.120 I feel like there's a thin line between a pan 0:01:37.240 --> 0:01:40.520 pizza and like a casserole or like a pot pie. 0:01:40.800 --> 0:01:42.800 It's really just a Midwestern hot dish. 0:01:42.840 --> 0:01:45.479 There you go, But anyways, welcome to our podcast, Daniel 0:01:45.480 --> 0:01:49.080 and Jorge Explain the Universe, a production of iHeartRadio. 0:01:48.680 --> 0:01:51.880 Where we love everything about the universe, the thick ready 0:01:51.920 --> 0:01:54.840 questions and the thin crunchy ones we wonder about how 0:01:54.920 --> 0:01:57.440 everything out there in the universe works. We take a 0:01:57.480 --> 0:02:00.640 big curiosity motivated by it, of the universe and try 0:02:00.640 --> 0:02:02.360 to chew through all of it for you. 0:02:02.720 --> 0:02:05.280 That's right, because the universe is a deep dish of 0:02:05.560 --> 0:02:09.120 amazing facts and incredible things happening in it, full of 0:02:09.160 --> 0:02:12.160 mysteries and wonderful conundrums for us to try to figure out. 0:02:12.240 --> 0:02:15.960 And while physics has made incredible progress in understanding the 0:02:15.960 --> 0:02:18.519 way the world works, we're still answering the kinds of 0:02:18.639 --> 0:02:22.840 questions we've been asking basically forever, just looking around us, 0:02:23.040 --> 0:02:25.840 seeing how the world is and wondering like, why is 0:02:25.880 --> 0:02:28.720 it this way? How did it get to be this way? 0:02:28.919 --> 0:02:33.000 Why does Deep Dish Pizza exist? Fundamental questions? That's what 0:02:33.040 --> 0:02:36.320 we ask here on the podcast, and why doesn't Daniel 0:02:36.360 --> 0:02:36.679 like them? 0:02:36.960 --> 0:02:38.919 We know why Deep Dish Pizza exist for the same 0:02:38.960 --> 0:02:41.400 reason vanilla ice cream exists, because you know, there's a 0:02:41.440 --> 0:02:44.720 whole spectrum of people out there and everybody loves different things. 0:02:44.919 --> 0:02:47.919 Are you saying the universe is kind of cheesy? I 0:02:47.919 --> 0:02:49.919 guess it will definitely give you a heart attack as well. 0:02:50.000 --> 0:02:51.840 There's no topping that joke, but yeah, we like to 0:02:51.840 --> 0:02:54.280 think about the universe and all of the perfecting things 0:02:54.320 --> 0:02:56.240 in it, like how did things come to be the 0:02:56.240 --> 0:02:58.440 way they are? Why are we here? And where are 0:02:58.480 --> 0:02:59.280 we in the universe? 0:02:59.280 --> 0:03:02.480 And what is One of the real, simple but enduring 0:03:02.639 --> 0:03:05.920 joys of being a curious person is just looking up 0:03:05.960 --> 0:03:08.359 at the night sky. Not just being amazed at it's 0:03:08.400 --> 0:03:10.760 beauty and odd at the depth of the view that 0:03:10.800 --> 0:03:13.760 you were looking at, but this shared feeling through time 0:03:13.880 --> 0:03:16.840 that humans one hundred years ago, a thousand years ago, 0:03:17.200 --> 0:03:20.840 twenty five thousand years ago probably looked up at almost 0:03:20.880 --> 0:03:23.200 the same night sky and wondered what was up there 0:03:23.240 --> 0:03:25.239 and why it looked the way it did, and whether 0:03:25.320 --> 0:03:27.200 it could have been different. 0:03:27.240 --> 0:03:30.560 Yeah, you're looking at the exact same sky that our 0:03:30.600 --> 0:03:34.280 ancestors did, full of stars, comments, and even a moon. 0:03:34.440 --> 0:03:36.840 And they probably asked the same question that maybe a 0:03:36.880 --> 0:03:39.240 lot of you have out there, which is, why do 0:03:39.280 --> 0:03:42.200 we have a moon? And is it made out of cheese? 0:03:42.520 --> 0:03:45.560 Is it just a big, flat, giant, floating deep dish 0:03:45.600 --> 0:03:46.000 of cheese. 0:03:47.520 --> 0:03:49.840 It's a spherical pizza. In the end, I have my 0:03:49.920 --> 0:03:51.480 spherical pizza theory of the moon. 0:03:51.640 --> 0:03:54.360 Do you do tell? Give us a slice of that 0:03:55.840 --> 0:03:56.720 knowledge there? 0:03:57.640 --> 0:03:58.680 All right? You called my bluff. 0:03:58.720 --> 0:04:02.839 I got nothing and it was a crusty joke. But yeah, 0:04:02.880 --> 0:04:05.680 sometimes we look out into the universe, into the night sky, 0:04:05.680 --> 0:04:08.000 and we wonder why are things there, and how did 0:04:08.000 --> 0:04:10.480 they come to be the way they are? What's going on? 0:04:10.720 --> 0:04:12.720 And it wasn't just our ancestors that looked up at 0:04:12.720 --> 0:04:15.160 the moon. It's like all of the planet that is 0:04:15.200 --> 0:04:17.200 looking up at the moon, right, it's feeling its facts 0:04:17.240 --> 0:04:19.720 and howling at it and rolling with the tides that 0:04:20.040 --> 0:04:22.000 go along with the moon. The moon has. It makes 0:04:22.000 --> 0:04:23.320 a big difference here on this planet. 0:04:23.400 --> 0:04:27.000 Yeah, and these are not just questions asked by amateur astronomers, 0:04:27.080 --> 0:04:30.119 but planet heiogeologist at the cunning edge are still trying 0:04:30.120 --> 0:04:32.560 to figure out the details of how everything came to 0:04:32.600 --> 0:04:33.479 be in our night sky. 0:04:34.000 --> 0:04:36.080 So to the other podcast, we'll be tackling the question 0:04:41.200 --> 0:04:44.400 how the planets get their moon or moons. Some planets 0:04:44.440 --> 0:04:45.400 have lots of moons, right. 0:04:45.360 --> 0:04:47.719 Yeah, that's right. It turns out our planet is quite 0:04:47.839 --> 0:04:50.600 unusual in having approximately one moon. 0:04:50.839 --> 0:04:53.440 So you do believe in the moon. The moon does exist, right. 0:04:54.480 --> 0:04:56.480 I can see the moon. I know it's there, But. 0:04:56.400 --> 0:04:58.160 How you know it's round? It always looks the same. 0:04:58.400 --> 0:05:01.480 Well, we've been to the moon, so we can see 0:05:01.600 --> 0:05:04.479 all around it, and you can tell that is round. Also, 0:05:04.520 --> 0:05:06.920 the curved edge between the bright side and the dark 0:05:06.960 --> 0:05:08.719 side of the moon tell us that it's going to 0:05:08.720 --> 0:05:09.119 be round. 0:05:09.400 --> 0:05:12.400 Oh right, you get sort of like the shadow of 0:05:12.440 --> 0:05:13.360 it tells you it's round. 0:05:13.960 --> 0:05:14.400 Exactly? 0:05:14.520 --> 0:05:16.560 Is it perfectly round? Is the Moon perfectly round? Or 0:05:16.600 --> 0:05:18.440 is it kind of an ellipsoid like the Earth. 0:05:18.560 --> 0:05:21.440 Nothing in the universe is perfectly round. There are no 0:05:21.640 --> 0:05:25.560 actual circles out there, maybe even not the event horizons 0:05:25.600 --> 0:05:28.080 of black holes due to quantum effects. So the Moon 0:05:28.120 --> 0:05:31.080 is definitely not perfectly round, and it's also pulled into 0:05:31.120 --> 0:05:34.040 something of a football shape thanks to the Earth's gravity. 0:05:34.120 --> 0:05:37.520 Tidal forces on the Moon by the Earth make it 0:05:37.560 --> 0:05:38.760 a little bit oblong. 0:05:39.080 --> 0:05:41.880 Whoa, I guess it's not spinning in the way that 0:05:41.920 --> 0:05:44.679 the Earth is so that you get this centropical force. 0:05:44.680 --> 0:05:46.240 But you're saying that the fact that the Earth is 0:05:46.279 --> 0:05:48.120 pulling on it kind of stretches it out. 0:05:48.279 --> 0:05:50.520 Yeah, it is spinning. It's just spinning at exactly the 0:05:50.600 --> 0:05:52.440 right rate so that the same side of it is 0:05:52.480 --> 0:05:56.720 always facing the Earth. This is called a tidal locking. Eventually, 0:05:56.720 --> 0:05:58.960 the Earth pulls on the Moon to make it oblong, 0:05:59.120 --> 0:06:01.719 and then they get stuck in this stable equilibrium where 0:06:01.720 --> 0:06:04.560 that long bit is always pointing towards the Earth because 0:06:04.600 --> 0:06:07.320 gravity on that long bit is a little stronger, so 0:06:07.360 --> 0:06:09.919 it's sort of like a pendulum dangling towards the Earth. 0:06:10.120 --> 0:06:11.680 Well, it is cool that we have a moon. I 0:06:11.680 --> 0:06:14.000 guess it would to inspire all of these songs and 0:06:14.040 --> 0:06:16.040 all these stories and legends about the moon. 0:06:16.320 --> 0:06:18.160 It is nice to have a moon. It lights up 0:06:18.240 --> 0:06:21.599 otherwise very dark nights, and it's something very close by 0:06:21.760 --> 0:06:23.520 to look at, right, So much of the rest of 0:06:23.520 --> 0:06:26.600 the night sky are just dots. They're so far away 0:06:26.640 --> 0:06:29.560 they look like pinpricks. But the Moon has features on it. 0:06:29.800 --> 0:06:31.359 I remember as a kid looking up at it and 0:06:31.400 --> 0:06:33.719 studying those and like wondering what it would be like 0:06:33.760 --> 0:06:35.800 to walk across it and to be on it, or 0:06:36.000 --> 0:06:38.240 to look at the Earth from the moon. It's cool 0:06:38.279 --> 0:06:40.680 that it's both in the night sky and kind of 0:06:40.680 --> 0:06:41.200 close by. 0:06:41.560 --> 0:06:44.520 Yeah, I guess it's kind of scary to think about it. Actually, 0:06:44.560 --> 0:06:47.600 it's just kind of swinging around the Earth. It's constantly 0:06:47.640 --> 0:06:50.040 falling around the Earth. That's what the Moon is doing. 0:06:50.160 --> 0:06:52.720 And it's big, Like you don't want to mess with 0:06:52.760 --> 0:06:53.279 the moon either. 0:06:53.640 --> 0:06:57.200 Yeah, the Moon is pretty massive. And not only is 0:06:57.200 --> 0:06:59.800 the Earth tugging on the Moon and forcing it to 0:07:00.040 --> 0:07:02.480 face us the same way, but the Moon is doing 0:07:02.480 --> 0:07:05.159 the same thing to Earth. Eventually, the Earth of the 0:07:05.160 --> 0:07:07.560 Moon will both be tidally locked to each other. 0:07:07.960 --> 0:07:12.760 Mmmmm, wait what does that mean? That means that we 0:07:12.760 --> 0:07:14.120 will be going around the moon. 0:07:14.360 --> 0:07:17.440 It means that, given enough time, the Moon will stay 0:07:17.440 --> 0:07:19.679 on the same side of the Earth. The Earth's spin 0:07:19.800 --> 0:07:23.360 and the Moon's spin will balance so that only one 0:07:23.480 --> 0:07:26.080 side of the Earth ever sees the Moon the same way, 0:07:26.120 --> 0:07:28.239 only one side of the Moon ever sees the Earth. 0:07:29.080 --> 0:07:31.600 Wait, what for real. When is that going to happen. 0:07:31.880 --> 0:07:33.800 It's not going to be for billions of years, but 0:07:33.840 --> 0:07:36.560 it has already had an impact, Like the rate that 0:07:36.600 --> 0:07:40.239 the Earth is spinning has slowed down to twenty four 0:07:40.240 --> 0:07:43.760 hours per spin over the last four billion years. Four 0:07:43.760 --> 0:07:46.040 billion years ago, it took about six hours for the 0:07:46.080 --> 0:07:49.120 Earth to spin, So the Moon is slowing down the 0:07:49.120 --> 0:07:52.600 spin of the Earth. Eventually, it will take about forty 0:07:52.640 --> 0:07:55.640 seven of our current days to spin the Earth. That 0:07:55.680 --> 0:07:57.680 will match the Moon's orbital period, and the Earth and 0:07:57.680 --> 0:08:00.480 the Sun will be tidally locked to each other. But 0:08:00.640 --> 0:08:02.720 that wouldn't be for billions of years, and that would 0:08:02.720 --> 0:08:05.040 be assuming that the Sun doesn't gobble the Earth first. 0:08:05.880 --> 0:08:08.720 Yeah, we would have bigger problems in the Moon at 0:08:08.760 --> 0:08:09.320 that point. 0:08:09.720 --> 0:08:11.600 But it would be kind of amazing if you could 0:08:11.640 --> 0:08:13.640 only see the Moon from one half of the Earth. 0:08:13.680 --> 0:08:15.360 It would mean you could grow up your whole life 0:08:15.400 --> 0:08:17.320 and not see the Moon, and then travel to another 0:08:17.360 --> 0:08:19.360 part of the Earth and see the Moon for the 0:08:19.400 --> 0:08:20.880 first time. That would be incredible. 0:08:21.080 --> 0:08:24.240 Whoa which sid gets to have the moon? Can they 0:08:24.240 --> 0:08:26.400 predict that? Or we even have the same We probably 0:08:26.400 --> 0:08:28.160 won't even have the same continents. 0:08:27.760 --> 0:08:30.920 Right, Yeah, not in billions of years exactly. 0:08:31.120 --> 0:08:33.199 I guess we have the moon to thank for having 0:08:33.200 --> 0:08:35.640 more time in our day. Then without the moon that 0:08:35.800 --> 0:08:36.960 things will be a lot more hectic. 0:08:37.120 --> 0:08:38.719 Yeah, that's true. Those of you who like to work 0:08:38.800 --> 0:08:41.000 late at night would have much shorter nights to get 0:08:41.040 --> 0:08:42.960 stuff done. 0:08:42.559 --> 0:08:44.720 I think the people during the day would also have 0:08:44.760 --> 0:08:48.960 a shorter time, right, But it is an interesting question 0:08:49.120 --> 0:08:52.079 how did we get this moon? Like how do planets 0:08:52.080 --> 0:08:53.960 get moons at all? And why do we only have 0:08:54.080 --> 0:08:56.679 one moon versus having lots of moons like other planets 0:08:56.679 --> 0:08:58.880 which have up to eighty four moons. 0:08:59.320 --> 0:09:01.640 It is really fun, fascinating question, and the answer tells 0:09:01.720 --> 0:09:04.559 us a lot about how solar systems form, whether our 0:09:04.600 --> 0:09:08.040 planet is weird, and maybe whether our solar system itself 0:09:08.160 --> 0:09:08.920 is kind of weird. 0:09:09.200 --> 0:09:11.080 Well, you can get all that from the moon. 0:09:12.480 --> 0:09:14.679 You can learn a lot just by asking questions. 0:09:14.840 --> 0:09:16.920 Well, as usual, we were wondering how many people out there? 0:09:16.960 --> 0:09:19.920 I thought about the question of where moons come from 0:09:19.960 --> 0:09:21.960 and how are they form? How do we get ours? 0:09:22.760 --> 0:09:25.079 So as usual Daniel went out there into the internet 0:09:25.080 --> 0:09:27.560 to ask people how do moons form? 0:09:27.720 --> 0:09:30.360 Thanks very much to everybody who participates in this segment 0:09:30.440 --> 0:09:32.240 of the podcast. If you've been listening for a while 0:09:32.320 --> 0:09:36.040 and thinking about participating, please let me encourage you. It's fun, 0:09:36.240 --> 0:09:39.679 it's easy. Everybody enjoys it. Write to me two questions 0:09:39.720 --> 0:09:41.840 at Danielandjorge dot com. 0:09:42.160 --> 0:09:43.920 So think about it for a second. How do you 0:09:43.960 --> 0:09:47.680 think planets get their moons? Here's what people had to say. 0:09:47.960 --> 0:09:52.800 I think that most moons form from cloud discs around planets, 0:09:53.160 --> 0:09:57.520 and that Satan's rings are a picture of that process 0:09:57.559 --> 0:09:58.000 going on. 0:09:58.600 --> 0:10:02.680 Moons on form? How planet form? So they're small rocks 0:10:02.679 --> 0:10:04.559 and then they hit each other and create bigger ones. 0:10:05.320 --> 0:10:08.240 So when a planet is created, maybe when it gets created, 0:10:08.280 --> 0:10:10.840 some debris goes out and then creates like a miniature 0:10:10.840 --> 0:10:12.120 planet aka a moon. 0:10:12.200 --> 0:10:16.319 Maybe I suppose the moon is just a small planet. 0:10:16.440 --> 0:10:19.760 It's kind of just a planet that gets trapped by 0:10:19.800 --> 0:10:21.960 another planet. Right, they're just rocks. 0:10:22.200 --> 0:10:25.800 There's got to be like at least six ways moon forms. 0:10:25.960 --> 0:10:29.199 I don't know, like things crashing together. Apparently we might 0:10:29.240 --> 0:10:33.360 have stolen the Moon from Venus. Maybe probably a bunch 0:10:33.360 --> 0:10:35.320 of other ways they could form too. 0:10:35.559 --> 0:10:40.720 I think Moon's form either just sort of alongside they're 0:10:40.840 --> 0:10:46.080 planet like Lucky, or from collisions like our own moon 0:10:47.440 --> 0:10:51.600 came from an impact. Those are, I guess, the only 0:10:51.640 --> 0:10:52.320 two I really know. 0:10:52.559 --> 0:10:56.480 I would say that this is a collisions between among 0:10:57.240 --> 0:11:01.640 asteroids planets, and then you have planet that has been 0:11:01.920 --> 0:11:04.320 hit by an asteroid, and a small chunk of this 0:11:04.400 --> 0:11:07.400 planet would be placed in a sort of an orbit, 0:11:07.480 --> 0:11:08.400 and then you get the Moon. 0:11:08.520 --> 0:11:11.240 I think it's when space dust is orbiting a planet 0:11:11.760 --> 0:11:15.760 and then it clumps together into the Moon eventually, or if, 0:11:15.840 --> 0:11:21.240 like an asteroid, is caught in the gravitational pool of 0:11:21.320 --> 0:11:24.640 a planet and falls into its orbit. 0:11:24.880 --> 0:11:28.240 I think Moon's form from asteroids and other bits of 0:11:28.280 --> 0:11:31.320 space debris that get trapped in a planet's orbit. 0:11:31.559 --> 0:11:33.960 I think that moon's form around planets the same way 0:11:34.120 --> 0:11:37.880 that planets form around stars. I think that basically there's 0:11:37.880 --> 0:11:40.319 a bunch of junk floating around the planet that aggregates 0:11:40.360 --> 0:11:42.319 into a moon or moons. 0:11:42.520 --> 0:11:46.280 All right, a lot of interesting answers here. Somebody said 0:11:46.320 --> 0:11:50.400 at least six ways, that's all they said, But only 0:11:50.520 --> 0:11:54.880 at least six he or she had six ways in mind. 0:11:55.000 --> 0:11:57.720 M reminds me that Paul Simon's song just get on 0:11:57.760 --> 0:12:01.319 the bus, gus don't need to discuss much. Yeah, there 0:12:01.400 --> 0:12:04.040 must be six ways to get a moon. 0:12:04.200 --> 0:12:07.320 Sounds like clickbait. Six ways so we can get a moon. 0:12:07.559 --> 0:12:11.040 The sixth one will totally amaze you. Maybe we should 0:12:11.040 --> 0:12:14.040 be learning from this listener and how to title our 0:12:14.440 --> 0:12:17.600 podcast episodes. Although that you hear BuzzFeed is going down, 0:12:17.640 --> 0:12:20.320 it's going out of business or BuzzFeed news. 0:12:20.440 --> 0:12:22.360 Do you think there's a lesson there for us podcasters? 0:12:22.600 --> 0:12:25.480 Yeah, I think there are six amazing lessons. The sixth 0:12:25.520 --> 0:12:27.160 one will totally astound you. 0:12:27.280 --> 0:12:28.160 I can't wait to hear. 0:12:28.360 --> 0:12:30.480 But yeah, a lot of interesting theories here from people. 0:12:30.880 --> 0:12:33.440 Some people think it happens from like a collision. Some 0:12:33.480 --> 0:12:37.199 people think we stole it from another planet? Is that true? 0:12:37.320 --> 0:12:39.480 The truth is that there are lots of different ways 0:12:39.520 --> 0:12:42.000 to get moons, and we'll dig into several of them today. 0:12:42.200 --> 0:12:44.839 M The sixth one will amaze you. 0:12:46.800 --> 0:12:47.520 If we get there. 0:12:47.679 --> 0:12:50.280 If we get that right, know for sure we'll get there. 0:12:50.760 --> 0:12:54.480 Question is how long before we get there? Will we 0:12:54.520 --> 0:12:56.840 do it before the hour is up? Towards a close call? 0:12:57.040 --> 0:12:59.360 All right, Well, let's start with the basics, Daniel, how 0:12:59.360 --> 0:13:01.160 would you define a moon? Like what is a moon? 0:13:01.440 --> 0:13:03.360 And what's the difference between a moon and like a 0:13:03.440 --> 0:13:06.320 satellite or an asteroid or just a space jump. 0:13:06.440 --> 0:13:08.800 Yeah, this is an interesting question in astronomy. We have 0:13:08.880 --> 0:13:12.000 all these categories we've invented to describe the kinds of 0:13:12.000 --> 0:13:14.720 things we've seen out there, and then we find things 0:13:14.720 --> 0:13:17.440 that break those categories, and it turns out there are 0:13:17.480 --> 0:13:20.520 no real hard divisions and bright lines between stuff. It's 0:13:20.559 --> 0:13:22.960 just sort of like where humans like to draw a 0:13:23.000 --> 0:13:25.679 dotted line between things, and so it's kind of a 0:13:25.720 --> 0:13:29.040 mess what a moon is signs. Originally they called these 0:13:29.040 --> 0:13:32.520 things natural satellites, Like when you look at Jupiter and 0:13:32.559 --> 0:13:34.880 you see things going around it, you call those satellites 0:13:34.880 --> 0:13:36.920 of Jupiter. And for a long time, like before the 0:13:36.960 --> 0:13:40.000 space age, the word moon just referred to the moon 0:13:40.040 --> 0:13:42.400 of the Earth, which is the name of our moon. 0:13:42.559 --> 0:13:46.600 But then we started launching artificial satellites, and so when 0:13:46.640 --> 0:13:49.880 Sputnik went up, people called it an artificial satellite. But 0:13:49.960 --> 0:13:52.400 that's sort of awkward and a mouthful, so people didn't 0:13:52.400 --> 0:13:55.680 like saying artificial satellite. They just start calling it satellite, 0:13:55.840 --> 0:13:59.079 and so that makes natural satellite kind of awkward. 0:13:58.679 --> 0:14:05.000 To say organic satellite exactly, or farm raised satellites. 0:14:04.600 --> 0:14:06.720 But natural satellite is kind of a mouthful, and so 0:14:06.960 --> 0:14:11.160 now people, even scientists, sometimes say moons. Technically, we have 0:14:11.280 --> 0:14:14.480 artificial satellites, things we have launched in due space, and 0:14:14.480 --> 0:14:18.080 then we have natural satellites, things that are in orbit anyway, 0:14:18.200 --> 0:14:20.560 naturally without the influence of humans. 0:14:20.720 --> 0:14:22.840 But wait, wait, I think I've seen NASA call the 0:14:23.320 --> 0:14:25.720 moons of Jupiter the moons of Jupiter. They never say 0:14:25.760 --> 0:14:26.880 the satellites of Jupiter. 0:14:27.040 --> 0:14:29.920 That's right. So technically we have artificial satellite and we 0:14:29.960 --> 0:14:32.880 have natural satellite, though typically we just say satellite for 0:14:33.000 --> 0:14:36.480 artificial satellite, and now we say moon for natural satellite, 0:14:36.520 --> 0:14:39.640 even in scientific publications and like official press releases. So 0:14:39.720 --> 0:14:42.760 now moon has come to mean natural satellite. 0:14:43.480 --> 0:14:45.120 I see. But I guess if you put the in 0:14:45.160 --> 0:14:47.600 front of it, then it's our moon. Like the moon 0:14:47.880 --> 0:14:50.840 is our moon, but then other moons are just moons. 0:14:51.440 --> 0:14:55.120 Yeah, exactly, the moon is our moon or Luna if 0:14:55.120 --> 0:14:57.880 you prefer. And moon with a lowercase M means any 0:14:58.000 --> 0:14:59.280 kind of natural satellite. 0:15:00.040 --> 0:15:01.960 I guess you can have rocks, and you can have 0:15:02.120 --> 0:15:02.840 the rock. 0:15:05.400 --> 0:15:07.400 Exactly. We have lots of rocks in orbit, but I 0:15:07.440 --> 0:15:09.880 don't think we have the rock in orbit yet, though 0:15:09.920 --> 0:15:12.240 I haven't seen fast and Furious twenty seven or whichever 0:15:12.280 --> 0:15:13.120 one has space. 0:15:14.000 --> 0:15:16.920 I'm assureing the next one there, they'll you know, speed 0:15:17.000 --> 0:15:19.160 up a ramp and somehow make it up to space 0:15:20.040 --> 0:15:23.080 and crash into a space station. While he jumps and 0:15:23.160 --> 0:15:24.920 also launches a rocket launcher. 0:15:25.360 --> 0:15:27.440 He's got to flex his muscles at some point. Another 0:15:27.520 --> 0:15:30.560 question is size, Like, is every object that's orbiting the 0:15:30.600 --> 0:15:33.920 Earth a moon? Every tiny little rock is at a 0:15:34.040 --> 0:15:37.440 moon of the Earth. Officially, there's no lower limit, right, 0:15:37.480 --> 0:15:40.520 Like every natural object with an orbit around the planet, 0:15:40.760 --> 0:15:42.440 technically you could call it a moon. 0:15:42.680 --> 0:15:44.760 Wait what I mean? No, at some point, it's just 0:15:44.800 --> 0:15:46.080 the rock, right. 0:15:45.920 --> 0:15:48.040 The moon is just a rock. Also makes the Moon 0:15:48.120 --> 0:15:51.760 different from other rocks orbiting the planet is just the size, 0:15:52.160 --> 0:15:55.920 and there is no official lower limit to the size 0:15:55.920 --> 0:15:58.040 of a moon. You could have a moon of any size, 0:15:58.080 --> 0:16:00.720 and any limit you place is going to be totally ourary, right. 0:16:01.640 --> 0:16:03.640 I wonder if the definition also has to do with 0:16:03.800 --> 0:16:07.560 how stable its orbit is. Like, if I just throw 0:16:07.560 --> 0:16:10.680 a rock and into space, it's kind of orbiting the 0:16:10.680 --> 0:16:12.200 Earth for a little bit, does that mean it's a. 0:16:12.160 --> 0:16:14.760 Moon that's not really in orbit? Right? I don't know 0:16:14.760 --> 0:16:16.960 how strong you are. Recently haven't seen you in a while, 0:16:17.040 --> 0:16:18.720 But I don't think you could throw a rock and 0:16:18.760 --> 0:16:21.360 actually get it into orbit. It has to be in orbit. 0:16:21.520 --> 0:16:24.880 Oh yeah, do you want to make that bet? I'll 0:16:24.880 --> 0:16:27.400 bet you a billion dollars because with a billion dollars 0:16:27.400 --> 0:16:29.720 I can come into space and throw the rock. 0:16:30.560 --> 0:16:32.400 If you get a rock orbiting the Earth, I will 0:16:32.440 --> 0:16:34.760 campaign NASA to let you name it officially. 0:16:35.480 --> 0:16:37.440 Well, if you get me on a rocket ship into 0:16:37.440 --> 0:16:40.040 space to throw a rock, we'll start the whole process. 0:16:40.160 --> 0:16:42.800 But we can look at the typical sizes of these things, 0:16:43.240 --> 0:16:45.880 and like in our Solar system there are a few 0:16:46.080 --> 0:16:49.440 hundred of these moons. There's six planets that have moons, 0:16:49.480 --> 0:16:51.520 for a total of two hundred and twenty six moons, 0:16:51.560 --> 0:16:54.920 and typically the planet to moon mass ratio is at 0:16:55.000 --> 0:16:58.280 least ten thousand to one, so moons typically have a 0:16:58.400 --> 0:17:01.200 much smaller mass than the planet they orbit. 0:17:01.440 --> 0:17:04.320 Wait, there are six planets in our Solar system with moons. 0:17:04.400 --> 0:17:05.520 Who doesn't have a moon? 0:17:05.840 --> 0:17:09.480 Neither Mercury nor Venus have moons. That's probably because they're 0:17:09.480 --> 0:17:12.680 too close to the Sun and so tidal disruption basically 0:17:12.720 --> 0:17:13.960 pulls those moons away. 0:17:14.240 --> 0:17:16.720 Oh interesting, and I just figured out that's probably what 0:17:16.760 --> 0:17:19.119 the listener meant when they said at least six ways. 0:17:19.240 --> 0:17:25.280 Oh nice. Probably every moon has a unique story, m 0:17:26.240 --> 0:17:29.800 they have their own origin story. Of course, our moon 0:17:29.920 --> 0:17:32.760 is a big exception to this ten thousand to one rule, right, 0:17:32.760 --> 0:17:35.240 because the mass of the Moon is about one eightieth 0:17:35.480 --> 0:17:37.840 of the mass of the Earth. It's like more than 0:17:37.960 --> 0:17:40.880 one percent of the mass of the Earth. So it's 0:17:40.880 --> 0:17:43.200 a big honk and moon it's very unusual. 0:17:43.600 --> 0:17:46.840 So most of the moons in the Solar System, some 0:17:46.920 --> 0:17:48.960 of them are as big as our moon, but you're 0:17:49.000 --> 0:17:52.280 saying that the ratio compared to their planet, most of 0:17:52.320 --> 0:17:52.919 them are small. 0:17:53.520 --> 0:17:56.120 Most of them are small exactly. And then there's the case, 0:17:56.119 --> 0:17:59.440 for example, of Pluto. Pluto has a moon which is Sharon, 0:17:59.520 --> 0:18:02.480 which is one eighth of its mass, and so like 0:18:02.520 --> 0:18:05.399 we call Pluto a dwarf planet, and we call Sharon 0:18:05.600 --> 0:18:08.440 a moon of Pluto. But you know, you could also 0:18:08.600 --> 0:18:11.920 argue that it's really like a dwarf planet binary system, 0:18:12.000 --> 0:18:14.120 which one is a planet and which one is the moon? 0:18:14.200 --> 0:18:15.560 It all gets kind of fuzzy. 0:18:15.680 --> 0:18:19.040 Whoa, it's like a double planet. 0:18:19.119 --> 0:18:19.399 Man. 0:18:21.000 --> 0:18:23.520 One way to distinguish the two scenarios, like having a 0:18:23.560 --> 0:18:26.400 double planet or a planet with a moon. Is whether 0:18:26.480 --> 0:18:30.160 the center of mass of the system is within the 0:18:30.200 --> 0:18:32.359 surface of one of them. If you find the point 0:18:32.400 --> 0:18:35.439 that averages where all the mass is, the point around 0:18:35.480 --> 0:18:38.159 which the two objects really are orbiting, if that is 0:18:38.400 --> 0:18:41.320 underground one of the two objects, and you call the 0:18:41.359 --> 0:18:43.359 more massive one a planet and the other one a moon. 0:18:43.560 --> 0:18:46.840 Otherwise you call it a binary system. Again, that's still 0:18:46.960 --> 0:18:49.200 kind of arbitrary, right, We're just like giving these things 0:18:49.280 --> 0:18:52.000 names and drawing lines between them. Really, there's just a 0:18:52.080 --> 0:18:54.520 bunch of different rocks out there in the universe orbiting 0:18:54.520 --> 0:18:54.880 each other. 0:18:55.760 --> 0:18:58.119 Except also, Pluto is not a planet, So can you 0:18:58.160 --> 0:19:00.959 have a moon around something that's not planet? Like can 0:19:01.040 --> 0:19:02.880 you can moon or can a moon have a moon? 0:19:03.800 --> 0:19:05.880 You can have a moon around a dwarf planet, though 0:19:05.920 --> 0:19:07.720 maybe you would want to call it a dwarf moon. 0:19:07.880 --> 0:19:11.640 I don't know. And it's possible in principle to have 0:19:11.800 --> 0:19:15.000 moons around moons. There are asteroids that have moons. 0:19:15.520 --> 0:19:19.040 Wait what, and you still call them moons, not master moons. 0:19:19.119 --> 0:19:21.880 Some people want to call them moonlits or moon moons 0:19:22.359 --> 0:19:23.080 like the moon of a. 0:19:23.040 --> 0:19:26.040 Moon or moony's or mini moons. 0:19:26.160 --> 0:19:28.199 And there are even some moons, like Rhea has its 0:19:28.240 --> 0:19:30.600 own ring system Saturn's moon Rhea. 0:19:30.760 --> 0:19:34.600 Wait what some moons can have rings? Yeah, because they 0:19:34.640 --> 0:19:36.439 have so many mini moons. 0:19:36.560 --> 0:19:39.600 If you're big enough that you dominate the gravitational environment nearby, 0:19:39.680 --> 0:19:41.280 then yeah, you can have your own rings. 0:19:41.320 --> 0:19:44.080 I mean, I guess technically anything can have a satellite, right, 0:19:44.119 --> 0:19:46.439 Like I can take a baseball, put in into space 0:19:46.520 --> 0:19:49.680 and then knock a you know, a speck of dust 0:19:49.680 --> 0:19:50.640 in orbit around it. 0:19:50.640 --> 0:19:53.200 Right, yeah, exactly. That wouldn't be a planet or even 0:19:53.200 --> 0:19:56.320 a dwarf planet, but it would have an orbiting object. 0:19:56.960 --> 0:19:59.960 Is that a natural satellite? I'm not quite sure. 0:19:59.800 --> 0:20:01.399 A what else do we know about moons? 0:20:01.520 --> 0:20:03.879 If you try to dig into the ancient history of moons, 0:20:03.920 --> 0:20:07.680 it gets quite confusing to read about because until Copernicus, 0:20:07.880 --> 0:20:10.679 moons were actually called planets, like the Moon itself was 0:20:10.720 --> 0:20:13.240 referred to as a planet. Like when you talked about 0:20:13.240 --> 0:20:16.240 astronomy in the fifteen hundreds, you said the planet Mars, 0:20:16.280 --> 0:20:20.360 the planet Venus, the planet Luna. And it wasn't until Kepler, 0:20:20.520 --> 0:20:22.560 who was thinking about how these things orbit each other, 0:20:22.560 --> 0:20:25.399 who had a better understanding of these orbits, that we 0:20:25.440 --> 0:20:28.439 started calling the moon a satellite of the Earth, and 0:20:28.480 --> 0:20:31.119 then the satellites of Jupiter are of course the moons 0:20:31.160 --> 0:20:34.119 of Jupiter. So there's a really fun interesting history to 0:20:34.160 --> 0:20:34.800 these words. 0:20:34.960 --> 0:20:37.359 Wait, really, so like, for a moment in human history, 0:20:37.400 --> 0:20:41.000 we thought the Moon was another planet orbiting the Solar System. 0:20:41.240 --> 0:20:42.920 Technically it is orbiting the Sun. 0:20:43.200 --> 0:20:45.240 Yeah, it is orbiting the Sun, and it is orbiting 0:20:45.240 --> 0:20:47.440 the Earth. Right, it's not that we thought the Moon 0:20:47.560 --> 0:20:50.119 was a planet like Mars. It's just that we categorized 0:20:50.160 --> 0:20:52.320 all these things the same way. All these words are 0:20:52.359 --> 0:20:54.680 just buckets, right, and they're just like grab a bunch 0:20:54.760 --> 0:20:56.600 of the stuff that's out there and gather it all 0:20:56.640 --> 0:20:59.600 into a conceptual bucket. And where the lines between these 0:20:59.640 --> 0:21:02.160 buckets is a little bit arbitrary. And so it used 0:21:02.160 --> 0:21:04.360 to be that we lumped the moon in with the planets. 0:21:04.680 --> 0:21:07.240 Now we have a separate category for things that orbit 0:21:07.280 --> 0:21:08.320 the planets. 0:21:09.280 --> 0:21:11.639 Shoot for the Moon. I guess when you're naming things, 0:21:11.760 --> 0:21:14.159 all right, well, let's get a little deeper into where 0:21:14.200 --> 0:21:16.920 the Moon came from, Where do moons in general come from, 0:21:16.960 --> 0:21:19.480 how do other planets get their moons, and what does 0:21:19.520 --> 0:21:22.399 it all mean about the history of the Solar System. 0:21:22.560 --> 0:21:37.479 But first let's take a quick break, all right, we're 0:21:37.520 --> 0:21:40.840 getting a little looney here talking about the moon and 0:21:40.880 --> 0:21:43.399 how we got it and how do planets get their moons. 0:21:43.560 --> 0:21:46.320 It is really fun in ancient question to wonder why 0:21:46.359 --> 0:21:48.560 that thing is in our sky and why Jupiter has 0:21:48.600 --> 0:21:51.359 more moons than we do. And if history had been different, 0:21:51.440 --> 0:21:53.320 would we have had a bunch of moons? What would 0:21:53.359 --> 0:21:55.919 it be like to live in that scenario? Could we 0:21:56.080 --> 0:21:59.240 sail as well? If the ties were crazy and complicated 0:21:59.359 --> 0:22:02.080 from having like fifteen different little moons? Hmmm? 0:22:02.400 --> 0:22:05.440 Interesting? Yeah, that would affect the tides, right, But that 0:22:05.440 --> 0:22:06.919 wouldn't affect navigation, would it. 0:22:06.920 --> 0:22:09.000 It wouldn't affect navigation, but it would affect when it's 0:22:09.040 --> 0:22:11.359 easy to launch your ships or not, and so it 0:22:11.400 --> 0:22:13.800 might affect lots of industries and exploration. 0:22:14.160 --> 0:22:16.199 M Also, if you're a were wolf, it would be 0:22:16.240 --> 0:22:19.840 pretty complicated, right, probably, just you know, just the planet ahead. 0:22:20.760 --> 0:22:22.840 Maybe you change into one kind of wolf for one 0:22:22.880 --> 0:22:24.879 moon and another kind of wolf for another moon, and 0:22:24.920 --> 0:22:27.440 like a Pomeranian for the little moon or a shitsu. 0:22:29.040 --> 0:22:31.840 Yeah, there you go, different moons for different breeds. 0:22:31.600 --> 0:22:33.600 Two moons up in the sky. Then you're a hybrid, right, 0:22:33.800 --> 0:22:35.520 This sounds like a fun science fiction story. 0:22:35.600 --> 0:22:37.200 It sounds like a great Ya novel. 0:22:39.080 --> 0:22:40.159 So many spin offs. 0:22:40.200 --> 0:22:42.560 All right, we talked about the word moon is kind 0:22:42.560 --> 0:22:45.879 of flexible and it's not quite super well defined, but 0:22:46.040 --> 0:22:48.200 basically it just kind of means like a big rock 0:22:48.280 --> 0:22:50.800 circling around a bigger rock. Right, that's right. 0:22:50.840 --> 0:22:53.320 It's a big rock orbiting another big rock. 0:22:53.520 --> 0:22:55.760 And as you said, six of the planets in our 0:22:55.800 --> 0:22:59.280 Solar system have them. Venus and Mercury don't because I 0:22:59.280 --> 0:23:01.879 guess they're too hot, you said. And if they had moons, 0:23:01.880 --> 0:23:04.840 then the Sun would have disrupted its orbit and probably 0:23:04.920 --> 0:23:06.960 made it crash into the planet, right or fly away. 0:23:07.080 --> 0:23:08.879 Yeah, it's all about the tidal forces. It makes it 0:23:08.920 --> 0:23:12.240 basically impossible for Mercury or Venus to have moons and 0:23:12.280 --> 0:23:14.560 to keep them. It's because they're so close to the Sun. 0:23:14.600 --> 0:23:18.080 It's not their actual temperature, it's the gravitational tidal forces 0:23:18.080 --> 0:23:18.640 from the Sun. 0:23:18.880 --> 0:23:21.399 All right, Well, what do we know about where moons 0:23:21.400 --> 0:23:22.440 come from and how they're form? 0:23:22.640 --> 0:23:24.280 So you can tell a lot about where a moon 0:23:24.320 --> 0:23:26.679 came from based on what it's made out of and 0:23:26.760 --> 0:23:29.439 how it's orbiting. If a moon is mostly in a 0:23:29.600 --> 0:23:32.800 circular orbit, and the circular orbit follows the tilt of 0:23:32.840 --> 0:23:36.600 the planet, so for example, it's orbiting around the equator 0:23:36.680 --> 0:23:39.399 in mostly a circle. Then it's very likely that that 0:23:39.520 --> 0:23:43.000 moon came from the same stuff that formed the planet. 0:23:43.280 --> 0:23:45.560 Remember how planets form in the beginning, it's a big 0:23:45.640 --> 0:23:48.679 cloud of gas and dust that forms the whole Solar System. 0:23:48.800 --> 0:23:50.680 Most of the gas is gobbled up by the star 0:23:50.760 --> 0:23:53.240 as it forms, and our Sun has ninety ninety percent 0:23:53.480 --> 0:23:55.359 of the mass of the Solar System. But if you 0:23:55.400 --> 0:23:57.719 get a little isolated pocket of heavy stuff that has 0:23:57.760 --> 0:24:00.439 its own gravity and can gather itself together, then you 0:24:00.440 --> 0:24:02.600 can get a planet. So a planet sort of forms 0:24:02.640 --> 0:24:05.200 the same way the Solar System does. It's the gravitational 0:24:05.280 --> 0:24:06.800 collapse of a big blob of. 0:24:06.760 --> 0:24:09.280 Stuff, right, And initially it's just kind of like a 0:24:09.320 --> 0:24:13.000 big cloud of rocks and dust that's spinning or has 0:24:13.080 --> 0:24:14.160 kind of an overall spin. 0:24:14.800 --> 0:24:17.240 Exactly. The reason you get moons around planets is the 0:24:17.280 --> 0:24:20.280 same reason you get planets around stars. Right. You don't 0:24:20.320 --> 0:24:22.480 just get all the mass of the Solar System collapsing 0:24:22.560 --> 0:24:24.560 into the Sun. You get these little pockets that have 0:24:24.640 --> 0:24:27.040 enough gravity to form themselves together and then are moving 0:24:27.080 --> 0:24:30.040 at high enough speed that they can resist falling into 0:24:30.119 --> 0:24:33.080 the Sun. Now, around those planets, of course, you also 0:24:33.160 --> 0:24:35.679 have little clouds of gas and dust. Some of it 0:24:35.720 --> 0:24:38.199 collapses into the planet, most of it, but some of 0:24:38.240 --> 0:24:41.680 it pulls itself together and has enough velocity to avoid 0:24:42.119 --> 0:24:45.320 falling into the planet. And so if you have enough 0:24:45.359 --> 0:24:47.600 velocity and you can pull yourself together, then you can 0:24:47.600 --> 0:24:50.439 form like a little planet's planet, a little miniature system 0:24:50.480 --> 0:24:52.680 around the planet, the same way the planet is going 0:24:52.720 --> 0:24:53.320 around the Sun. 0:24:53.560 --> 0:24:56.360 Right, because I guess gravity. That's how gravity works, right, 0:24:56.400 --> 0:24:59.600 Like everything is attracted to everything else. It's not just 0:24:59.640 --> 0:25:01.960 like we're attract it to the Sun or juice attracted 0:25:02.200 --> 0:25:06.159 to the planet Earth. It's like I'm attracted to my 0:25:06.320 --> 0:25:08.800 car and to this base bomb, the base will attracted 0:25:08.840 --> 0:25:10.520 to me. And so if we were out in space, 0:25:11.160 --> 0:25:13.040 we would both be falling towards the Earth, but then 0:25:13.080 --> 0:25:15.040 we would there would also be an attraction between us. 0:25:15.080 --> 0:25:18.000 And sometimes I think what you're saying is that if 0:25:18.200 --> 0:25:21.520 a clump of dirt and rocks when the planet is forming, 0:25:21.560 --> 0:25:24.040 it's kind of far enough out there, it will clump 0:25:24.080 --> 0:25:25.879 together before it clumps with the Earth. 0:25:26.040 --> 0:25:28.680 Yeah, that's exactly right. And there's sort of two steps there. 0:25:29.119 --> 0:25:32.760 One is have enough velocity, like are you spinning fast 0:25:32.840 --> 0:25:35.880 enough that you can basically get in orbit around the planet, 0:25:35.960 --> 0:25:38.560 And that's how you get like a protoplanetary disc. The 0:25:38.600 --> 0:25:41.240 planet forms and have some stuff out there that hasn't 0:25:41.280 --> 0:25:43.920 fallen into the planet. So initially it's like a disc 0:25:44.280 --> 0:25:47.120 and that can pull itself together using gravity into a ring. 0:25:47.359 --> 0:25:49.280 And then there's a question of whether that ring can 0:25:49.320 --> 0:25:52.439 pull itself together into a moon or not. Sometimes it 0:25:52.480 --> 0:25:55.800 stays a ring and sometimes it forms a moon, and 0:25:55.840 --> 0:25:58.879 that depends on how close you are to that planet. 0:25:59.119 --> 0:26:01.680 If you're really really close to that planet, close to 0:26:01.720 --> 0:26:04.159 than what we call the Roche limit, then tile forces 0:26:04.160 --> 0:26:05.879 from the planet are too strong. If you try to 0:26:05.880 --> 0:26:08.280 form a moon, the tile forces will tear it apart. 0:26:08.560 --> 0:26:11.720 If you're outpast the Roche limit, then the tidle forces 0:26:11.720 --> 0:26:14.240 are weak and you can gather together into a moon. 0:26:14.440 --> 0:26:16.879 So you have to have enough velocity to avoid falling 0:26:16.920 --> 0:26:19.200 into the planet, and then you have to be out 0:26:19.280 --> 0:26:22.119 past the Roche limit to have a ring get turned 0:26:22.160 --> 0:26:22.840 into a moon. 0:26:23.880 --> 0:26:26.760 Because I think, as we've talked about before, gravity kind 0:26:26.800 --> 0:26:29.439 of depends on the distance between two things. Right. So 0:26:29.840 --> 0:26:32.560 if you're really close to the Earth, then like the 0:26:32.560 --> 0:26:34.560 difference between one side of the Moon and the other 0:26:34.600 --> 0:26:38.040 side of the Moon is they experience very different gravitational forces. 0:26:38.080 --> 0:26:40.960 But maybe if you're far out and beyond this limit, 0:26:41.040 --> 0:26:44.560 then you don't see this difference in pull from the 0:26:44.600 --> 0:26:48.119 Earth between one and and the other, which kind of 0:26:48.200 --> 0:26:49.040 lets you clump together. 0:26:49.680 --> 0:26:52.119 You'll still always feel that difference, right, and like the 0:26:52.160 --> 0:26:55.280 Moon does feel that difference. That's why we talked about earlier. 0:26:55.359 --> 0:26:58.199 The Moon is a football. It is being pulled by 0:26:58.200 --> 0:27:00.560 the Earth's tidal forces, but it's far and away that 0:27:00.640 --> 0:27:03.320 those tidle forces are not strong enough to tear it apart. 0:27:03.440 --> 0:27:06.520 The roach limit for the Earth is around ten thousand kilometers. 0:27:06.680 --> 0:27:08.840 The Moon is like three hundred and eighty five thousand 0:27:08.880 --> 0:27:11.880 kilometers away, so it's well past the roach limit. If 0:27:11.920 --> 0:27:14.000 the Moon was much much closer, if it was like 0:27:14.119 --> 0:27:16.720 less than ten thousand kilometers from the surface of the Earth, 0:27:17.000 --> 0:27:19.640 the Earth would tear it apart with those tidal forces 0:27:19.680 --> 0:27:22.000 into a massive ring system instead. 0:27:21.920 --> 0:27:23.800 Where some of the rocks in that ring are going 0:27:23.840 --> 0:27:24.600 at different speeds. 0:27:24.640 --> 0:27:26.320 Right, it would be pretty cool to see the Moon 0:27:26.440 --> 0:27:28.840 get torn up into rocks. Not all of them would 0:27:28.960 --> 0:27:31.760 have the same velocity originally as the Moon. I'm sure 0:27:31.800 --> 0:27:34.159 it would be somewhat destructive and chaotic. Some of them 0:27:34.160 --> 0:27:35.600 would end up falling to the Earth, some of them 0:27:35.640 --> 0:27:37.199 would get lost, and some of them would end up 0:27:37.200 --> 0:27:37.680 in orbit. 0:27:37.880 --> 0:27:40.400 Cool And I think that, as you said, also applies 0:27:40.400 --> 0:27:42.000 to planets, right like you kind of have to be 0:27:42.040 --> 0:27:44.280 a certain distance away from the Sun just to form 0:27:44.320 --> 0:27:44.920 a planet, too. 0:27:45.200 --> 0:27:47.439 Exactly, if you're too close to the Sun, then the 0:27:47.480 --> 0:27:51.640 Sun's tidal forces, which are very powerful, will pull you apart. 0:27:51.800 --> 0:27:53.760 So the roche limit for the Sun is like seven 0:27:53.840 --> 0:27:56.520 hundred and fifty thousand kilometers. So if the Earth was 0:27:56.600 --> 0:27:59.200 that close to the Sun, not only will we be fried, 0:27:59.240 --> 0:28:01.240 of course, but the Sun would pull us apart with 0:28:01.359 --> 0:28:05.120 its tidal forces. As you said, the gravitational force depends 0:28:05.160 --> 0:28:07.719 on the distance, and so the Sun's gravit on the 0:28:07.760 --> 0:28:09.720 near side of the Earth would be so much more 0:28:09.760 --> 0:28:11.879 powerful than the Sun's gravity in the far side of 0:28:11.880 --> 0:28:14.520 the Earth. It's effectively pulling us apart, and the Earth 0:28:14.880 --> 0:28:17.439 is not strong enough to survive if it's closer than 0:28:17.480 --> 0:28:20.879 seven hundred and fifty thousand kilometers. Fortunately, we're like one 0:28:20.960 --> 0:28:24.120 hundred and fifty million kilometers from the Sun, so we're 0:28:24.119 --> 0:28:27.360 nowhere near the Roche limit. And this isn't like an exact, 0:28:27.440 --> 0:28:29.840 hard and fast number, it's like approximate. It depends on 0:28:29.880 --> 0:28:32.119 the mass of the object, and it depends on structural 0:28:32.119 --> 0:28:34.080 features of it, Like if you had a planet made 0:28:34.080 --> 0:28:36.520 out of diamond, it could get closer to the Sun 0:28:36.680 --> 0:28:38.080 than a planet made out of gravel. 0:28:39.360 --> 0:28:41.920 But I guess generally speaking, it depends on the size 0:28:41.960 --> 0:28:44.080 of the thing in the middle, Like the Sun has 0:28:44.120 --> 0:28:47.200 a very big roach limit and the Earth as a 0:28:47.200 --> 0:28:47.719 smaller one. 0:28:47.800 --> 0:28:49.920 Yeah, that's true. You can get closer to the Earth, 0:28:50.160 --> 0:28:51.960 then you can get to the Sun. But if you 0:28:51.960 --> 0:28:54.560 see a moon around a planet and it's orbiting in 0:28:54.640 --> 0:28:58.040 a circular orbit and it mostly has the same angle 0:28:58.080 --> 0:29:01.120 or momentum as the planet, then you suspect that probably 0:29:01.280 --> 0:29:03.800 came from the same stuff that made the planet, and 0:29:03.840 --> 0:29:06.360 when that planet coalesced into stuff, not all of it 0:29:06.400 --> 0:29:08.920 got turned into the planet, some of it got left 0:29:08.960 --> 0:29:12.320 over and turned into a moon. So circular orbits with 0:29:12.400 --> 0:29:16.960 the same anglermentum probably came from the same protoplanetary disk 0:29:17.320 --> 0:29:18.280 that formed the planet. 0:29:19.800 --> 0:29:22.880 Okay, So then if a moon is orbiting a planet 0:29:23.080 --> 0:29:26.800 kind of in the same plane as the planet is spinning, 0:29:27.560 --> 0:29:30.280 then most likely they're like siblings, kind of like they 0:29:30.320 --> 0:29:33.000 were born at the same time from the same stuff. 0:29:33.680 --> 0:29:36.360 Yeah, I suppose you could say so though, sort of 0:29:36.360 --> 0:29:38.520 the scenario where like one twin is really big and 0:29:38.560 --> 0:29:39.440 the other one is tiny. 0:29:39.560 --> 0:29:41.280 Yeah, they're fraternal twins. 0:29:42.280 --> 0:29:44.960 Exactly, and probably one it's pretty grumpy about not getting. 0:29:44.760 --> 0:29:46.600 As much of dinner, all right. So that's one way 0:29:46.600 --> 0:29:49.200 that maybe a moon can form, which is like it's 0:29:49.240 --> 0:29:51.320 borne along with the planet, and you can sort of 0:29:51.320 --> 0:29:53.880 tell which ones those are, Which of those do we 0:29:53.920 --> 0:29:56.120 have in our Solar system, Like, is our moon one 0:29:56.120 --> 0:29:56.400 of them? 0:29:56.480 --> 0:29:58.760 Our moon is not one of those. Our moon is 0:29:58.760 --> 0:30:01.200 actually a very weird case. Most of the moons in 0:30:01.200 --> 0:30:03.680 the Solar System do not have nice circular orbits that 0:30:03.720 --> 0:30:05.880 are orbiting with the planets. In fact, most of them 0:30:06.200 --> 0:30:09.600 have elliptical orbits that have weird tilts. And that suggests 0:30:09.600 --> 0:30:11.280 a completely different history for how. 0:30:11.160 --> 0:30:14.520 That moon formed, necessarily, because like I wonder if maybe 0:30:14.720 --> 0:30:16.560 the moon was formed as a sibling, but then it 0:30:16.640 --> 0:30:21.320 got not by something and then it got a skewed orbit. 0:30:21.400 --> 0:30:24.040 Yeah, that's certainly possible, but we think that most of 0:30:24.080 --> 0:30:27.240 the ones with skewed orbits, that with tilted orbits that precess, 0:30:27.280 --> 0:30:31.480 for example, are probably captured objects, things that came nearby 0:30:31.600 --> 0:30:34.479 and were grabbed onto by the gravity of that planet. 0:30:34.560 --> 0:30:36.560 You're right, it's possible for moon to be formed with 0:30:36.560 --> 0:30:38.760 a planet and then get tilted through a collision. You 0:30:38.760 --> 0:30:40.680 can tell the difference by looking at what that moon 0:30:40.760 --> 0:30:42.600 is made out of. Is it made out of basically 0:30:42.600 --> 0:30:45.280 the same stuff that formed the planet, or is it 0:30:45.320 --> 0:30:47.800 made out of something totally weird and different. So that's 0:30:47.800 --> 0:30:50.640 sort of like the key piece of information for distinguishing. 0:30:50.240 --> 0:30:53.160 Like a DNA test prove of your siblings or not. 0:30:54.120 --> 0:30:56.800 All right, well, then what does not having a circular 0:30:56.920 --> 0:30:58.480 orbit tell you about the moon. 0:30:58.560 --> 0:31:01.120 It tells you that probably it was captured, that the 0:31:01.160 --> 0:31:04.000 planet is formed, and the moon comes from somewhere else. 0:31:04.040 --> 0:31:07.000 It's like an asteroid or a dwarf planet or something 0:31:07.280 --> 0:31:09.640 that was floating around and just came too close to 0:31:09.680 --> 0:31:12.560 this massive object and its gravity took over. There's a 0:31:12.640 --> 0:31:15.360 vicinity of a massive object we called the hill sphere, 0:31:15.360 --> 0:31:18.320 which is the region sort of where its gravity dominates, 0:31:18.320 --> 0:31:21.520 where everything else that's far away can basically be neglected, 0:31:21.560 --> 0:31:23.960 and if an object passes within the hillsphere, it's a 0:31:24.000 --> 0:31:25.840 candidate for getting captured. 0:31:26.000 --> 0:31:28.520 But isn't that kind of weird? Or isn't it kind 0:31:28.520 --> 0:31:30.840 of unlikely that you'll just kind of catch a big 0:31:30.960 --> 0:31:33.120 rock out there and it'll have just the right speed 0:31:33.160 --> 0:31:35.960 and distance to fall into a stable orbit, Like, aren't 0:31:35.960 --> 0:31:38.320 stable orbits kind of hard to get into? 0:31:38.560 --> 0:31:40.840 It is unlikely and it is weird. You're right. You 0:31:40.840 --> 0:31:43.520 have to match the radius and the velocity. Like the 0:31:43.600 --> 0:31:46.080 reason the Earth is in a stable orbit is because 0:31:46.120 --> 0:31:48.720 it has the right velocity for our radius. You have 0:31:48.720 --> 0:31:51.560 to be moving in a certain velocity at a given radius. 0:31:51.280 --> 0:31:53.240 Like if we slowed down at all in our orbit, 0:31:53.280 --> 0:31:55.480 we would start to spiral into the Sun. Right. 0:31:55.600 --> 0:31:58.600 First orbit is actually quasi stable. So if we slowed 0:31:58.640 --> 0:32:01.640 down a little bit, gravitational forces what actually pushes back 0:32:01.680 --> 0:32:03.920 towards our orbit? But that's a whole other topic. 0:32:04.280 --> 0:32:05.920 Like if you slow down a lot, though. 0:32:06.000 --> 0:32:07.720 Yes, if we slowed down a lot, we would fall 0:32:07.760 --> 0:32:09.480 in towards the Sun. If we sped up a bunch, 0:32:09.640 --> 0:32:12.360 we would be ejected from the Solar system. And so 0:32:12.440 --> 0:32:14.920 you have to have this match between these two quantities, 0:32:15.320 --> 0:32:17.680 and it's not trivial for that to happen. Not only 0:32:17.680 --> 0:32:19.080 do you have to have the right velocity and the 0:32:19.160 --> 0:32:21.719 right radius, but you also have to lose energy in 0:32:21.800 --> 0:32:24.080 order to fall into an orbit. Any object that falls 0:32:24.120 --> 0:32:27.400 into the Solar System by definition has enough energy to 0:32:27.560 --> 0:32:30.560 escape because it came from outside the Solar System. And 0:32:30.600 --> 0:32:33.440 so if it just passes through on like a hyperbolic trajectory, 0:32:33.800 --> 0:32:36.440 you know it has enough kinetic energy to climb out 0:32:36.440 --> 0:32:38.920 of the gravitational well of the Solar System because it 0:32:38.960 --> 0:32:41.560 came from outside the gravitational well. So in order to 0:32:41.600 --> 0:32:43.360 get captured it not only does it have to come 0:32:43.400 --> 0:32:45.760 in at the right radius and the right velocity, got 0:32:45.800 --> 0:32:48.280 to lose a little bit of energy so that no 0:32:48.360 --> 0:32:50.840 longer has the energy to escape. That can happen if 0:32:50.840 --> 0:32:53.560 you like drag on the atmosphere the planet a little bit, 0:32:53.600 --> 0:32:55.720 which gives you a little bit of friction, or maybe 0:32:55.720 --> 0:32:58.800 another moon steals a little bit of your energy. So like, 0:32:58.840 --> 0:33:01.440 the more moons you have and the puffier your atmosphere, 0:33:01.560 --> 0:33:03.920 the more likely you are to be able to capture 0:33:03.960 --> 0:33:05.440 an object that comes near you. 0:33:06.120 --> 0:33:09.080 M it's kind of interesting to think of this idea 0:33:09.160 --> 0:33:11.719 that planets like the Earth has a kind of a 0:33:11.720 --> 0:33:14.240 halo kind of right, like a big sphere around it. 0:33:14.240 --> 0:33:17.640 It's basically like a giant net. Like whatever falls into it, 0:33:17.640 --> 0:33:19.040 it's gonna get sucked in. 0:33:19.400 --> 0:33:21.200 Yeah, exactly. And if you fall in too far and 0:33:21.240 --> 0:33:23.000 you slow don too far, then of course you're going 0:33:23.040 --> 0:33:25.600 to burn up as you enter the atmosphere. So it's 0:33:25.600 --> 0:33:28.520 a delicate operation. This is also think that sometimes a 0:33:28.560 --> 0:33:31.400 pair of objects that are orbiting each other can fall 0:33:31.440 --> 0:33:33.920 in the hillsphere and then one of them can get 0:33:33.960 --> 0:33:36.400 captured and the other one can get ejected. So all 0:33:36.440 --> 0:33:38.800 these sort of complicated things have to go just right 0:33:39.240 --> 0:33:41.360 in order for a planet to capture a moon. 0:33:42.200 --> 0:33:45.520 And by capturing, that's a nice word for stealing, right right, 0:33:45.560 --> 0:33:46.920 I guess you're like trapping. 0:33:48.560 --> 0:33:50.720 You're dancing, you're dancing with them, have of that? 0:33:50.880 --> 0:33:51.800 Oh I see see? 0:33:52.160 --> 0:33:52.360 Is that? 0:33:52.400 --> 0:33:55.480 Where our that listener who mentioned earlier that maybe we 0:33:55.560 --> 0:33:57.840 got our moon by stealing it from Venus? Is that? 0:33:58.120 --> 0:33:59.080 Is there some truth to that? 0:34:00.080 --> 0:34:02.880 We don't think that our moon was stolen from Venus, 0:34:02.880 --> 0:34:04.400 but we do think that lots of the moons of 0:34:04.480 --> 0:34:06.920 Jupiter and Saturn, for example, and these guys have like 0:34:07.000 --> 0:34:10.839 dozens of moons come from scattered objects in the early 0:34:10.920 --> 0:34:14.240 Solar system. Remember that very early on things were forming. 0:34:14.400 --> 0:34:16.560 There may even have been more planets than the ones 0:34:16.600 --> 0:34:20.080 we have now, and everything was quite chaotic. So now 0:34:20.080 --> 0:34:22.560 we have sort of an orderly solar system where everything 0:34:22.640 --> 0:34:25.280 is in place because it's been in place for so long, 0:34:25.719 --> 0:34:27.960 and things that were not in place have been lost 0:34:28.040 --> 0:34:30.279 or captured or fallen into the Sun. But in the 0:34:30.320 --> 0:34:32.279 early days there were a lot of things going in 0:34:32.320 --> 0:34:35.480 crazy orbits and crazy trajectories, and so Jupiter and Saturn 0:34:35.600 --> 0:34:37.279 sort of like hoovered up a bunch of them. 0:34:37.560 --> 0:34:39.520 So like, if you look at the moons of Jupiter, 0:34:39.560 --> 0:34:41.600 for example, they're not all going to be like lined 0:34:41.640 --> 0:34:44.240 up in a plane like our solar system. They probably 0:34:44.280 --> 0:34:46.680 all have like crazy orbits around Jupiter. 0:34:46.760 --> 0:34:49.000 Right, Yeah, that's exactly right, and that's why we think 0:34:49.000 --> 0:34:51.360 that most of these were captured. Also, in the cases 0:34:51.360 --> 0:34:53.200 that we've been able to try to study what these 0:34:53.239 --> 0:34:55.239 moons are made out of, they're all made out of 0:34:55.280 --> 0:34:57.360 totally different things, and so it doesn't look like they 0:34:57.480 --> 0:34:59.920 formed from the same sort of scoop of solar systems 0:35:00.120 --> 0:35:01.879 off that Jupiter did. 0:35:02.320 --> 0:35:03.960 That's what you were saying, like you can check the 0:35:04.040 --> 0:35:06.720 DNA basically the DNA of the moon and the planet 0:35:06.800 --> 0:35:08.600 to see if they came from the same stuff, and 0:35:08.640 --> 0:35:10.080 sometimes they don't, right. 0:35:10.640 --> 0:35:13.080 Yeah, exactly. That's still tricky to do because we haven't 0:35:13.200 --> 0:35:15.840 landed on those moons and like really taken samples that 0:35:15.880 --> 0:35:18.600 we can study. But we can like do spectroscopy, we 0:35:18.600 --> 0:35:20.640 can see the light that bounces off of them, we 0:35:20.640 --> 0:35:23.239 can see what they emit, these kind of things. We 0:35:23.320 --> 0:35:25.640 have done some flybys, and so we have ideas for 0:35:25.719 --> 0:35:27.719 what these moons are probably made out of. 0:35:29.120 --> 0:35:31.520 And in the early Solar system, like you said, things 0:35:31.560 --> 0:35:34.400 were like there were probably like rock giant rocks flying 0:35:34.400 --> 0:35:37.279 all over the place, and so it wouldn't be that 0:35:37.360 --> 0:35:40.360 weird for some of them to fall into orbit around 0:35:40.600 --> 0:35:42.960 like a passing Jupiter or Centurn. So is that how 0:35:43.000 --> 0:35:45.000 we got our moon? Did we capture it or steal 0:35:45.000 --> 0:35:45.640 it from somebody? 0:35:45.719 --> 0:35:47.600 So we think our moon is unusual because it doesn't 0:35:47.640 --> 0:35:50.719 fall into either of these categories. We don't think that 0:35:50.719 --> 0:35:53.080 the Moon was formed with the Earth. We also don't 0:35:53.080 --> 0:35:56.800 think that a wholly formed moon was captured by the Earth. Instead, 0:35:56.840 --> 0:35:59.239 we think it comes from a collision. We think that 0:35:59.280 --> 0:36:02.480 there was the proto Earth, this early planet, and then 0:36:02.480 --> 0:36:05.680 there was another Mars like planet that came by and 0:36:05.760 --> 0:36:09.480 smashed into the Earth, and there was this incredible collision 0:36:09.680 --> 0:36:12.440 where essentially these two planets merged, but they left a 0:36:12.600 --> 0:36:16.360 huge debris ring, and then that debris ring pulled together 0:36:16.680 --> 0:36:17.479 and made the Moon. 0:36:17.719 --> 0:36:20.759 Does our moon have an orbit that's around our equator 0:36:20.920 --> 0:36:21.640 or is it tilted? 0:36:21.760 --> 0:36:24.360 The Moon doesn't have a totally random orbit relatively angular 0:36:24.400 --> 0:36:27.120 momentum of the Earth, because the two objects are essentially 0:36:27.160 --> 0:36:30.799 formed by the combined angularmentum of this collision. So you 0:36:30.840 --> 0:36:33.200 get this collision and basically you start from scratch. You 0:36:33.239 --> 0:36:35.600 have a new blob of stuff which is then going 0:36:35.640 --> 0:36:38.480 to coalesce again into a planet and a moon. And 0:36:38.520 --> 0:36:40.960 so there is a relationship of course between the Earth's 0:36:40.960 --> 0:36:43.719 spin and the Moon's orbit, and that's because they come 0:36:43.760 --> 0:36:46.800 from this combined blob from this collision. 0:36:46.840 --> 0:36:49.040 It's pretty dramatic. I think you can look up videos 0:36:49.040 --> 0:36:51.920 of simulations of it online. It's like the Earth, the 0:36:51.960 --> 0:36:54.600 proto Earth before Earth was just hanging out and then 0:36:54.640 --> 0:36:57.640 this giant rock just slams into it. It all sort 0:36:57.640 --> 0:37:00.880 of explodes together, but then gravity pulls it together into 0:37:01.200 --> 0:37:02.320 Earth and the Moon. 0:37:02.239 --> 0:37:04.640 Exactly, and the early Moon, we think, was much much 0:37:04.760 --> 0:37:07.480 closer to the Earth, something like a tenth of its 0:37:07.520 --> 0:37:11.080 current orbit, and then over time it spirals out and 0:37:11.200 --> 0:37:13.800 ends up becoming tightly locked to the Earth. One reason 0:37:13.840 --> 0:37:15.399 we think this is that we've been to the Moon 0:37:15.440 --> 0:37:17.480 and we've been able to land on it and study 0:37:17.480 --> 0:37:19.680 what it's made out of, and we see that it's 0:37:19.719 --> 0:37:21.480 made out of a lot of stuff that's very very 0:37:21.520 --> 0:37:23.719 similar to what the Earth is made out of, which 0:37:23.760 --> 0:37:26.200 suggests that they do have some sort of common origin. 0:37:27.320 --> 0:37:30.400 And does the Earth also sort of have moon like 0:37:30.840 --> 0:37:32.920 materials in it that are not like the rest of 0:37:32.960 --> 0:37:33.360 the Earth. 0:37:33.440 --> 0:37:34.920 Well, we see that the Earth and the Moon have 0:37:34.960 --> 0:37:37.279 a lot of very similar elements, which sugg they all 0:37:37.320 --> 0:37:39.920 came from the same stuff, But the Moon has fewer 0:37:39.920 --> 0:37:42.960 of like volatile elements things that vaporize at low temperatures 0:37:43.040 --> 0:37:45.920 we're probably lost in this high energy event, and the 0:37:45.960 --> 0:37:48.480 Moon has smaller gravity and so it's not able to 0:37:48.680 --> 0:37:50.719 recapture these things the way the Earth did, so the 0:37:50.760 --> 0:37:53.360 Earth and the Moon don't have exactly the same kinds 0:37:53.400 --> 0:37:55.680 of stuff. The Moon also has a sort of surprisingly 0:37:55.840 --> 0:37:59.800 small iron core which overall makes the Moon have lower density. 0:38:00.080 --> 0:38:02.560 Simulations confirmed that this is what you would expect from 0:38:02.560 --> 0:38:05.200 this kind of collision, that the Moon was formed more 0:38:05.280 --> 0:38:07.479 out of the sort of external debris and the Earth 0:38:07.560 --> 0:38:10.320 sort of got a bigger sampling of the core stuff. 0:38:11.280 --> 0:38:13.440 I guess the Moon is also smaller, so it doesn't 0:38:13.440 --> 0:38:17.560 have as much gravity compressing it, right, making it denser exactly. 0:38:17.960 --> 0:38:19.839 And when they study like what's inside the Moon, they 0:38:19.880 --> 0:38:23.000 find samples that suggest the Moon was molten down to 0:38:23.080 --> 0:38:26.240 like a surprising depth. And you don't expect the small 0:38:26.280 --> 0:38:29.120 body like the Moon to have the gravitational pressure to 0:38:29.320 --> 0:38:31.880 like melt its inerts the way the Earth does. So 0:38:31.920 --> 0:38:34.040 they think that the Moon was probably molten because of 0:38:34.080 --> 0:38:36.760 this collision, not because of its like gravitational pressure. 0:38:37.120 --> 0:38:37.440 Hmm. 0:38:37.640 --> 0:38:40.640 Interesting. And I think they also found like the same 0:38:40.880 --> 0:38:43.600 cheese inside of the Moon as some of the cheese 0:38:43.680 --> 0:38:47.000 we have on Earth too, Right, that's part of the theory. 0:38:49.000 --> 0:38:51.560 Yeah, they found pan pizzas rejected on the surface of 0:38:51.560 --> 0:38:52.840 the Moon that nobody could eat. 0:38:53.000 --> 0:38:56.520 That's right, the same mozzarella, cheese, the same cows, even 0:38:57.280 --> 0:39:00.399 space cows. All right, well, that's the origin of our moon. 0:39:00.520 --> 0:39:03.360 Let's get a little bit into what that means about 0:39:03.400 --> 0:39:07.279 the formation of all moons and the formation of our 0:39:07.320 --> 0:39:10.279 whole Solar system, why we're here, and why are things 0:39:10.320 --> 0:39:12.880 the way they are. But first, let's take another quick break. 0:39:25.600 --> 0:39:27.799 All right, we are coming face to face with the 0:39:28.000 --> 0:39:31.440 lunacy here in the podcast talking about the origin of 0:39:31.520 --> 0:39:35.440 moons and in particular our moon. You're saying, it's interesting because, 0:39:35.719 --> 0:39:37.839 like our moon is sort of a combination of how 0:39:37.920 --> 0:39:40.520 some of these other moons can form. Right, Like, we 0:39:40.600 --> 0:39:43.040 had a proto planet Earth, and when there was a 0:39:43.160 --> 0:39:47.080 visitor that was flying around came near us, it sort 0:39:47.080 --> 0:39:49.400 of got captured or collided with our Earth, and then 0:39:49.440 --> 0:39:51.680 it all became a big mess. And out of that mess, 0:39:52.280 --> 0:39:54.360 you know, the Earth and the Moon forms sort of 0:39:54.400 --> 0:39:58.400 a siblings, but also not siblings, because there was it 0:39:58.480 --> 0:40:01.000 came from a different planet. The stuff. 0:40:01.120 --> 0:40:03.799 There was a big fight early on, and we were left 0:40:03.800 --> 0:40:06.279 over cleaning up the mess. Yeah, it is really fascinating, 0:40:06.320 --> 0:40:09.000 and I love this sort of archaeology, this like detective 0:40:09.040 --> 0:40:13.280 story figuring out what happened billions of years ago, reconstructing 0:40:13.280 --> 0:40:15.279 the story from the clues that are left behind, these 0:40:15.320 --> 0:40:17.919 really subtle hints. You know, why does the Moon seem 0:40:17.960 --> 0:40:19.560 to be made of the same stuff as the Earth, 0:40:19.560 --> 0:40:22.040 but it doesn't have sort of a close circular orbit 0:40:22.040 --> 0:40:24.480 the way you would expect. Why exactly is it so big? 0:40:24.719 --> 0:40:27.719 These stories are really fascinating because we missed so much 0:40:27.760 --> 0:40:29.960 of the Solar System history. You know, like billions of 0:40:30.120 --> 0:40:33.440 years happened with crazy fireworks in the sky and we 0:40:33.440 --> 0:40:35.520 weren't here to look at it. But we can still 0:40:35.520 --> 0:40:36.840 get hints about what happened. 0:40:37.040 --> 0:40:39.759 Hmmm, do you think that's an official job title out there, 0:40:39.760 --> 0:40:42.000 like space archaeologists. 0:40:42.760 --> 0:40:46.000 Space murder mystery, you know, exactly. 0:40:45.800 --> 0:40:49.400 Give me like Indiana solo a combination of Indiana Jones 0:40:49.480 --> 0:40:50.240 and Hands solo. 0:40:51.600 --> 0:40:54.359 And you know, we're still learning stuff about moons, like 0:40:54.560 --> 0:40:57.719 Mars has some funny moons, Phobos and Demos, And the 0:40:57.800 --> 0:41:01.319 smaller of those two moons, Demos, is really tiny. It's 0:41:01.360 --> 0:41:04.800 only like nine miles across, has a really weird shorwt 0:41:04.800 --> 0:41:07.160 of blobby shape to it, and for a long time 0:41:07.160 --> 0:41:10.239 people thought it was probably a captured asteroid because of 0:41:10.280 --> 0:41:13.359 its orbit, but they recently send an orbiter very very 0:41:13.360 --> 0:41:16.160 close to it, super close approach by this spacecraft from 0:41:16.160 --> 0:41:18.839 the UA Emirates. Actually it's called Hope, and they were 0:41:18.840 --> 0:41:21.240 able to study what it's made out of and discover 0:41:21.400 --> 0:41:24.440 that it has sort of the same carbon and organics 0:41:24.480 --> 0:41:27.680 that Mars does, unlike the asteroids, sort of like the 0:41:27.800 --> 0:41:30.640 DNA test you were saying before, which means that Demos 0:41:30.680 --> 0:41:34.600 probably is a chunk of Mars that got blown off 0:41:34.719 --> 0:41:36.480 in some sort of prehistoric collision. 0:41:36.600 --> 0:41:38.400 Isn't that also kind of the theey of how we 0:41:38.440 --> 0:41:41.360 got life on Earth, like a possible way that maybe 0:41:41.400 --> 0:41:43.480 Mars got hit by something. It threw a bunch of 0:41:43.600 --> 0:41:46.279 rocks out into space. Some of them became Demos, the 0:41:46.320 --> 0:41:48.360 moon of Mars, and maybe some of them came to 0:41:48.400 --> 0:41:50.240 Earth bringing like little bacteria. 0:41:50.280 --> 0:41:53.880 Perhaps we're very sure that rocks from Mars have landed 0:41:53.920 --> 0:41:56.320 on Earth. We have found them and their geology matches 0:41:56.360 --> 0:41:59.160 Mars and doesn't match Earth. So there's no controversy about 0:41:59.160 --> 0:42:03.000 whether visions from asteroids on planets can knock stuff off 0:42:03.000 --> 0:42:05.320 into outer space and have it land on other planets. 0:42:05.440 --> 0:42:08.120 Whether there's life in those rocks that then seeded life 0:42:08.160 --> 0:42:12.120 on Earth totally open question. There was this famous misdiscovery 0:42:12.400 --> 0:42:14.959 about twenty years ago when they found these weird little 0:42:15.000 --> 0:42:18.000 shapes inside a Martian rock on Earth, and they made 0:42:18.000 --> 0:42:20.319 this announcement that they were certain that there was life 0:42:20.320 --> 0:42:23.000 in them, that these shapes could only be made by life. 0:42:23.160 --> 0:42:25.960 But then later analysis demonstrated that you could make those 0:42:25.960 --> 0:42:29.399 things without life. So there's no concrete proof that life 0:42:29.440 --> 0:42:32.840 has traveled between planets on an asteroid, but it's totally 0:42:32.920 --> 0:42:35.799 possible for it to happen. And Demos definitely is a 0:42:35.920 --> 0:42:38.680 chunk of Mars floating in space. Sort of like if 0:42:38.680 --> 0:42:40.960 you went out into space and you found like Manhattan 0:42:41.239 --> 0:42:43.759 floating out in space, you'd be like, whoa, Where'd this 0:42:43.800 --> 0:42:44.280 come from? 0:42:44.520 --> 0:42:45.920 Yeah, well people wonder about that. 0:42:46.640 --> 0:42:50.879 Now, what's the story? How did Manhattan get so weird? 0:42:50.880 --> 0:42:53.799 Where did New Yorkers come from their lunatics? 0:42:53.880 --> 0:42:56.319 But they have the best pizza, right, so I don't 0:42:56.360 --> 0:42:57.560 want to have to go out of space to get 0:42:57.600 --> 0:42:59.480 my pizza. 0:43:00.200 --> 0:43:02.839 You just insulted everyone in Chicago. He lost a big 0:43:02.920 --> 0:43:03.960 chunk of our listenership. 0:43:04.080 --> 0:43:06.520 I love Chicago, I love Chicago wins, and I love 0:43:06.560 --> 0:43:09.239 the Chicagoans love Chicago pizza. That's all fine with me. 0:43:09.480 --> 0:43:11.640 All right, Well, what does all of this tells about 0:43:11.680 --> 0:43:14.319 the formation of the Solar System and how we ended 0:43:14.400 --> 0:43:16.200 up where we are and how we are. 0:43:16.440 --> 0:43:18.320 It's a story that we are still unraveling. 0:43:18.400 --> 0:43:18.520 Right. 0:43:18.560 --> 0:43:21.080 We're still learning about our moon, We're still learning about 0:43:21.080 --> 0:43:25.520 our neighbor's moons. We're still discovering moons. Right. Saturn recently 0:43:25.560 --> 0:43:28.160 past Jupiter. I think in the number of moons that 0:43:28.239 --> 0:43:30.799 it has, each one tells us a little bit of 0:43:30.840 --> 0:43:33.160 the story of the Solar system, and what we're looking 0:43:33.200 --> 0:43:35.799 for now are like more details for that story. As 0:43:35.840 --> 0:43:39.560 you said earlier, we're asking questions like can moons have moons? 0:43:39.800 --> 0:43:42.120 A lot of people think that it's impossible for the 0:43:42.120 --> 0:43:44.600 same reason that like Mercury and Venus don't have moons 0:43:44.719 --> 0:43:47.600 from the tidal forces of the Sun, that Jupiter's moons 0:43:47.640 --> 0:43:50.120 probably can't have their own moons because of the tidal 0:43:50.200 --> 0:43:53.840 forces of Jupiter. But you know, Saturn's moon Rhea probably 0:43:53.840 --> 0:43:57.640 has rings which even though they're disrupted by the title forces, 0:43:57.719 --> 0:44:00.479 they can still be in orbit around Rhea. And there's 0:44:00.560 --> 0:44:03.560 like hundreds of minor planets deep out there in the 0:44:03.560 --> 0:44:06.440 Solar system that do have their own moons, like Pluto. 0:44:06.600 --> 0:44:09.280 But beyond that, we're also looking into other solar systems 0:44:09.320 --> 0:44:11.480 to try to understand whether the moons that we have 0:44:11.800 --> 0:44:15.359 are weird or typical? Right, Like, we only so far 0:44:15.520 --> 0:44:18.000 have this one solar system to study at this level 0:44:18.040 --> 0:44:20.160 of detail. Twenty years ago, we were able to see 0:44:20.200 --> 0:44:22.759 planets around other stars, which tells us a lot about 0:44:22.760 --> 0:44:25.560 whether the planets in our solar systems are weird. Now 0:44:25.560 --> 0:44:28.160 we're pushing those boundaries to try to look for moons 0:44:28.280 --> 0:44:32.480 in other solar systems. This thing we call exo moons 0:44:32.520 --> 0:44:34.800 to try to discover if the distribution of moons that 0:44:34.840 --> 0:44:38.440 we have is strange or pretty typical in the universe. 0:44:38.520 --> 0:44:40.640 Well, that's wild. How are we seeing moons and other 0:44:40.680 --> 0:44:43.839 planets outside of our solar system? Can we see them 0:44:43.920 --> 0:44:46.280 or do we have to infer them from the gravity. 0:44:46.560 --> 0:44:48.840 So there's a few ways that we discover planets, and 0:44:48.880 --> 0:44:51.680 we can try to apply those ways to discover moons. 0:44:51.960 --> 0:44:54.839 One of the early ways we discovered planets around other 0:44:54.880 --> 0:44:58.640 stars was seeing their gravitational impact on the star, and 0:44:58.680 --> 0:45:01.280 that would wiggle the star and cause like a change 0:45:01.320 --> 0:45:04.080 in the frequency of the light, this Doppler shift, and 0:45:04.120 --> 0:45:06.160 so we could discover that there was something pulling on 0:45:06.239 --> 0:45:08.480 that star. We don't think that method will work for 0:45:08.600 --> 0:45:11.480 discovering moons because it's really hard to distinguish the gravitational 0:45:11.520 --> 0:45:13.560 effect of a little moon around a planet from the 0:45:13.560 --> 0:45:16.120 planet itself. What we do think is possible is the 0:45:16.200 --> 0:45:20.000 transit method, this eclipse method, where a planet passes in 0:45:20.000 --> 0:45:22.000 front of a star and dips the light that comes 0:45:22.040 --> 0:45:24.239 from it, And if that happens in a regular way, 0:45:24.320 --> 0:45:27.600 we can tell that these little microeclipses come from a planet. Well, 0:45:27.600 --> 0:45:29.960 if those eclipses have their own little dips in them, 0:45:30.280 --> 0:45:33.719 because the moon going around the planet sometimes blocks this 0:45:33.880 --> 0:45:36.480 life from the star and sometimes doesn't, then you can 0:45:36.520 --> 0:45:42.000 discover moons around those planets. So like microeclipses within microeclipses. 0:45:42.120 --> 0:45:45.200 Wow, exo eclipses exo exo moon eclipses. 0:45:45.320 --> 0:45:47.919 Yeah, they're like eclipses squared. And we don't have any 0:45:47.960 --> 0:45:50.680 confirmed exo moons yet, though there are a couple of 0:45:50.719 --> 0:45:54.480 candidates from the Kepler telescope that look promising, but people 0:45:54.480 --> 0:45:58.279 can't yet agree whether that actually is the discovery of 0:45:58.320 --> 0:46:01.920 a moon. And more recently, we've developed this incredible technology 0:46:01.960 --> 0:46:05.280 to do direct imaging of exoplanets, like telescopes that actually 0:46:05.360 --> 0:46:09.440 take pictures of planets around other stars. Blows my mind. 0:46:09.480 --> 0:46:11.560 I never thought that would be possible. A lot of 0:46:11.560 --> 0:46:13.960 it involves like blocking out the light from the star 0:46:14.040 --> 0:46:16.440 itself so you can see the ring around it. And 0:46:16.480 --> 0:46:19.799 sometimes that lets us see planets being formed. So we 0:46:19.800 --> 0:46:22.439 can see, for example, a star with a planetary disc 0:46:22.560 --> 0:46:24.960 around it. And in one case we have a direct 0:46:25.040 --> 0:46:28.520 image of a protoplanetary disc which seems to have a 0:46:28.560 --> 0:46:31.520 planet with its own disc around it. So like you 0:46:31.520 --> 0:46:33.480 can see the planet and it's got like a bunch 0:46:33.480 --> 0:46:36.040 of stuff around it, and maybe that stuff will form 0:46:36.080 --> 0:46:36.680 into a moon. 0:46:37.920 --> 0:46:39.040 You can see the rings in it. 0:46:39.239 --> 0:46:41.520 Yeah, exactly. You can see this disc that's going to 0:46:41.640 --> 0:46:44.200 form it either into rings or moons or something. 0:46:44.280 --> 0:46:46.359 Yeah, it's pretty mind blowing because I wonder like if 0:46:46.360 --> 0:46:48.040 a lot of people know that you can actually see 0:46:48.040 --> 0:46:50.279 the moons of Jupiter kind of with your naked eye, 0:46:50.360 --> 0:46:52.319 or at least with a small telescope. You don't need 0:46:52.360 --> 0:46:54.399 like a super amazing telescope. You can just use something 0:46:54.400 --> 0:46:55.839 you can buy for your house and you can see 0:46:55.840 --> 0:46:56.640 the moons of Jupiter. 0:46:56.719 --> 0:46:58.960 Yeah, it doesn't take a fancy telescope. It was one 0:46:59.000 --> 0:47:01.040 of the first things that Galla saw when he pointed 0:47:01.040 --> 0:47:02.799 a telescope at the sky. It was one of the 0:47:02.800 --> 0:47:04.560 first people to ever do this, and he saw the 0:47:04.640 --> 0:47:06.640 moons of Jupiter. It's not hard. You can do it, 0:47:06.640 --> 0:47:09.520 and it's pretty exciting to see Jupiter expand from this 0:47:09.640 --> 0:47:11.799 tiny dot you can see with the naked eye to 0:47:11.920 --> 0:47:14.480 this whole orbital system with its own dynamics. 0:47:14.840 --> 0:47:18.200 H pretty cool. All right. Well, one thing that's day 0:47:18.200 --> 0:47:20.560 announced recently is that we're sending more people to the Moon. 0:47:20.719 --> 0:47:22.960 That's right, if Elon Musk ever gets that starship off 0:47:23.000 --> 0:47:23.400 the ground. 0:47:23.520 --> 0:47:26.319 No, the new artem is missions right, It isn't one 0:47:26.360 --> 0:47:27.920 of the plants to send more people to the moon. 0:47:28.040 --> 0:47:30.040 Yeah, that's exciting. It'd be cool to go back to 0:47:30.080 --> 0:47:32.279 the Moon. With all of our advanced technology, we can 0:47:32.440 --> 0:47:35.360 take more detailed measurements. We can map its magnetic field, 0:47:35.400 --> 0:47:38.399 we can understand its geology and its history even better. Yeah. 0:47:38.440 --> 0:47:40.200 I wonder why kind of pizza they would eat there though? 0:47:40.880 --> 0:47:43.520 It's a deep dish because there's not much that much gravity. 0:47:43.560 --> 0:47:45.160 So can you have a deep dish pizza? 0:47:46.000 --> 0:47:48.279 Probably every pizza would rise a lot more because there 0:47:48.280 --> 0:47:49.400 isn't gravity, right. 0:47:49.320 --> 0:47:51.480 Oh, my goodness. In space, every pizza is a deep 0:47:51.520 --> 0:47:53.719 dish pizza. That's why you're not going to Earth. 0:47:53.840 --> 0:47:57.080 Danu or maybe astronaut pizza is just freeze dried and 0:47:57.120 --> 0:48:00.880 gross no matter where it comes from. 0:48:01.239 --> 0:48:03.239 I guess there's something one way to find out to 0:48:03.280 --> 0:48:06.799 take the podcast to space. All right, Well that kind 0:48:06.800 --> 0:48:09.480 of answers our question. How the Moon's form basically two 0:48:09.520 --> 0:48:13.360 main ways, right, They either capture something flying by in space, 0:48:13.600 --> 0:48:16.480 or they form together with the planet, or some combination 0:48:16.560 --> 0:48:20.319 of the tube where something comes from space crashes into you, 0:48:20.560 --> 0:48:22.880 creates a big mess, and then you both sort of 0:48:22.920 --> 0:48:24.640 form together or reform together. 0:48:24.800 --> 0:48:26.880 And the incredible thing is that by looking at the 0:48:26.880 --> 0:48:29.840 Moon today we can mostly figure out how that happened, 0:48:29.840 --> 0:48:32.160 how this huge space rock ended up in orbit around 0:48:32.200 --> 0:48:33.160 the planet. Yeah. 0:48:33.160 --> 0:48:34.680 And the cool thing is that you can see the 0:48:34.719 --> 0:48:37.000 Moon almost every night. Every night you step outside of 0:48:37.000 --> 0:48:39.840 your house, you can see this giant rock floating in 0:48:39.920 --> 0:48:43.319 space there for us to see, pretty shiny, pretty bright. 0:48:44.560 --> 0:48:47.240 It's nice to have one big, fat moon. I agree. 0:48:47.480 --> 0:48:49.799 All right, Well, we hope you enjoyed that. Thanks for 0:48:49.880 --> 0:48:51.680 joining us, See you next time. 0:48:59.480 --> 0:49:02.360 Thanks for listening, and remember that Daniel and Jorge Explain 0:49:02.400 --> 0:49:06.399 the Universe is a production of iHeartRadio. For more podcasts 0:49:06.400 --> 0:49:11.080 from iHeartRadio, visit the iHeartRadio, app, Apple podcasts, or wherever 0:49:11.120 --> 0:49:12.840 you listen to your favorite shows.