WEBVTT - How big can a comet get? 0:00:08.520 --> 0:00:12.080 Hey, Katie, how do you like your gelato? Definitely with 0:00:12.280 --> 0:00:16.160 two scoops of basically any flavor. So it's all about 0:00:16.239 --> 0:00:19.319 quantity for you, that right, It's all about gelato. What's 0:00:19.360 --> 0:00:23.120 to complain about? All right? So is that also true 0:00:23.440 --> 0:00:27.200 for things out in space? Bigger is always better? I mean, 0:00:27.720 --> 0:00:31.160 the sun is gigantic, and I only have good things 0:00:31.160 --> 0:00:33.519 to say about that. So you know, all right, you 0:00:33.520 --> 0:00:36.760 should leave a five star review for our star? What 0:00:36.960 --> 0:00:40.560 about things like comets? Is bigger always better there? I mean, 0:00:40.720 --> 0:00:43.000 especially if they're made out of ice cream? So a 0:00:43.040 --> 0:00:47.200 big old comet streaking above our sky leaving a trail 0:00:47.240 --> 0:00:50.120 of sprinkles? Who doesn't want that? Well? What if it's 0:00:50.159 --> 0:00:54.000 sprinkling its way towards the earth like impact style? Well 0:00:54.040 --> 0:01:13.080 then I can order a triple gelato with no consequences. Hi. 0:01:13.240 --> 0:01:16.440 I'm Daniel. I'm a particle physicist and a professor at 0:01:16.520 --> 0:01:19.360 U C Irvine, and I am Katie, and I'm the 0:01:19.360 --> 0:01:24.880 host of the podcast Creature Feature. And I enjoy ice 0:01:24.959 --> 0:01:27.800 cream as much as I enjoy physics, which is a 0:01:27.800 --> 0:01:31.360 lot but not too much moderation in all things? Is 0:01:31.400 --> 0:01:34.720 that the vibe I'm getting? That's probably right? In both cases, 0:01:34.760 --> 0:01:37.000 if I have too much physics at once, I also 0:01:37.040 --> 0:01:40.039 get a brain freeze. Or did you mean like after 0:01:40.120 --> 0:01:42.160 a nice large meal you need a little bit of 0:01:42.160 --> 0:01:44.560 physics to sort of like balance out the palette. I mean, 0:01:44.600 --> 0:01:50.880 I think that's what digestion is, right, Absolutely well, Welcome 0:01:50.920 --> 0:01:54.520 to the podcast Daniel and Jorge explain the universe in 0:01:54.560 --> 0:01:58.800 which we try to digest the entire universe. We serve 0:01:58.880 --> 0:02:00.600 it up on a platter d you and give it 0:02:00.600 --> 0:02:03.120 to you in tiny little spoonfuls, hoping that helps you 0:02:03.200 --> 0:02:07.040 understand the mysteries of black holes, the incredible froth and 0:02:07.120 --> 0:02:11.119 quantum nature of reality, the mysteries, the puzzles, the insides, 0:02:11.200 --> 0:02:13.520 all of it. We sprinkle delicious treats on top and 0:02:13.600 --> 0:02:16.320 serve it up to you. It's the Moves Bouge of 0:02:16.800 --> 0:02:21.600 particle physics. My typical co host and friend, Jorge Champ 0:02:21.639 --> 0:02:23.720 can't be here today, so as usual we are joined 0:02:23.760 --> 0:02:25.880 by the wonderful Katie. Katie, thank you very much for 0:02:26.080 --> 0:02:28.440 joining us again today. Yeah, happy to be here again. 0:02:28.520 --> 0:02:30.600 Want to point out Jorge and I have never been 0:02:30.639 --> 0:02:34.440 seen together in the same room. Raises some questions, doesn't it? 0:02:34.840 --> 0:02:37.440 Does that mean that Jorge transforms into you or you 0:02:37.480 --> 0:02:40.480 transform into Jorge. At this point, who can say who 0:02:40.560 --> 0:02:43.079 is who Isn't that the lesson of jack Bile and 0:02:43.200 --> 0:02:46.880 Hide exactly the quantum mechanical interpretation of modern literature. It's 0:02:46.880 --> 0:02:49.440 really the jackal Hide wave function, that's right, got to 0:02:49.480 --> 0:02:52.000 collapse the wave form. Well, we are happy to talk 0:02:52.080 --> 0:02:55.160 physics with either Katie or Jorge, so thanks for joining us. 0:02:55.360 --> 0:02:58.240 And while we nibble on our gelato, we ponder the 0:02:58.360 --> 0:03:01.480 mysteries of the universe, but we also ponder the mysteries 0:03:01.560 --> 0:03:04.840 of our own neighborhood. You might think that astronomers have 0:03:05.040 --> 0:03:08.400 our backyard the Solar system, mostly figured out, and that 0:03:08.480 --> 0:03:11.960 the open questions in physics revolve around things very very 0:03:12.000 --> 0:03:14.720 far away and far in the future and far back 0:03:14.800 --> 0:03:17.880 in time. But you might be surprised to learn that 0:03:18.000 --> 0:03:22.239 our own neighborhood remains something of a mystery to us. Now, 0:03:22.320 --> 0:03:26.239 that doesn't seem right, because my understanding as we've already 0:03:26.280 --> 0:03:30.680 got real estate on Mars and have every crevice, every 0:03:30.720 --> 0:03:33.000 crater of the Moon mapped out, So how can there 0:03:33.000 --> 0:03:35.960 be any mysteries left here in our solar system? Well, 0:03:36.000 --> 0:03:38.880 it's probably true that some entrepreneur has planned the first 0:03:38.960 --> 0:03:42.920 gelato stand on Mars that's pretty close to Earth. And 0:03:42.960 --> 0:03:46.120 you know, the Solar System is actually really really vast. 0:03:46.360 --> 0:03:49.480 The Earth is tucked in really tightly, very close to 0:03:49.600 --> 0:03:53.400 the Sun, but outpassed Jupiter and outpassed the icy planets. 0:03:53.520 --> 0:03:56.800 There's a lot of mysterious stuff going on. What's the 0:03:56.920 --> 0:04:01.000 furthest we've ever sent any of our instruments out into space. 0:04:01.440 --> 0:04:03.880 We haven't gotten past our own Solar System. We have 0:04:03.960 --> 0:04:06.960 sent some probs really deep into space, just like launch 0:04:07.040 --> 0:04:09.640 them out there and see how long they last. And 0:04:09.680 --> 0:04:12.480 the one that's the furthest out the object the humans 0:04:12.480 --> 0:04:15.480 have built that has gone the deepest into space is 0:04:15.600 --> 0:04:19.120 Voyager one. But even Voyager one hasn't officially left the 0:04:19.160 --> 0:04:22.840 Solar System yet. In around three hundred years, it might 0:04:22.880 --> 0:04:26.080 reach the outskirts of the Solar System, but unfortunately it's 0:04:26.120 --> 0:04:29.039 power runs out in five so by the time it 0:04:29.080 --> 0:04:31.680 gets there, it'll just be a dead lump. Well so 0:04:32.000 --> 0:04:39.320 we so, you know, you'll be fifty gelato by that point. Anyway, 0:04:39.560 --> 0:04:42.040 I can only hope. So there could be some space 0:04:42.080 --> 0:04:45.440 gopers in our space backyard and we wouldn't even know it. 0:04:45.720 --> 0:04:48.520 That's right. There are mysteries right here in our own backyard. 0:04:48.520 --> 0:04:51.440 There are things we do not understand. One way to 0:04:51.520 --> 0:04:54.440 explore the mist to send probes deep into the outskirts 0:04:54.440 --> 0:04:56.719 of the Solar System. But that's pretty slow. You know, 0:04:56.760 --> 0:04:59.000 it takes years for things to get out there because 0:04:59.040 --> 0:05:01.960 it's so day far away. You know, it takes months 0:05:02.000 --> 0:05:03.960 to get to Venus or Mars, but to get out 0:05:03.960 --> 0:05:06.640 to Pluto can take a decade. To get further out 0:05:06.960 --> 0:05:09.640 deep into the farthest reaches of the Solar System to 0:05:09.680 --> 0:05:13.080 explore its fringes takes even longer. But there's another way 0:05:13.120 --> 0:05:15.960 to study our deep, mysterious backyard, and that's to wait 0:05:16.000 --> 0:05:19.640 for it to come to us. Because sometimes things out 0:05:19.640 --> 0:05:23.240 from the outskirts do fall into the Solar System, and 0:05:23.279 --> 0:05:26.640 these things are called comets. They accelerate to incredible speeds 0:05:26.640 --> 0:05:28.840 as they whip around the Sun and then go back 0:05:28.960 --> 0:05:32.400 to where they came from. So how do comets find us? 0:05:32.560 --> 0:05:35.240 Did they see some kind of flyer way out in 0:05:35.360 --> 0:05:39.159 space It at the Earth sale about two point five 0:05:39.240 --> 0:05:42.760 light years away? Is it just random chance? Are they 0:05:42.960 --> 0:05:45.640 drawn into our Solar system? They hang out there in 0:05:45.680 --> 0:05:47.760 the deep reaches of the Solar System, and we're not 0:05:47.839 --> 0:05:51.279 exactly sure what sometimes triggers them to fall in. It 0:05:51.360 --> 0:05:53.719 might be the passing of a nearby star, or the 0:05:53.760 --> 0:05:57.479 gravitational tug of the Milky Way, or something else. Entirely, 0:05:57.480 --> 0:06:00.560 we don't even really understand what's going on out there 0:06:00.720 --> 0:06:04.279 and what is out there waiting to maybe fall into 0:06:04.320 --> 0:06:06.200 the Solar System. For those of you who have seen 0:06:06.240 --> 0:06:09.000 don't look up and worry about things hitting the Earth. 0:06:09.360 --> 0:06:12.120 You don't have to worry too much about things like asteroids, 0:06:12.120 --> 0:06:15.000 those rocks that are orbiting the inner Solar system. But 0:06:15.120 --> 0:06:18.120 comets are much more dangerous because they can be hard 0:06:18.120 --> 0:06:20.680 to predict, and they're moving much more quickly when they 0:06:20.800 --> 0:06:23.560 do enter the Solar System. I watched Don't Look Up, 0:06:23.560 --> 0:06:26.600 and I find it interesting because I think there is 0:06:26.640 --> 0:06:31.240 a big divide in terms of how realistic people find 0:06:31.279 --> 0:06:34.640 it in Those who are either climate scientists or even 0:06:34.480 --> 0:06:39.080 in any related science find it very realistic, whereas other 0:06:39.120 --> 0:06:41.760 people think, oh, this this is just two on the nose, 0:06:41.839 --> 0:06:45.320 it's too outrageous. You mean, like the social response to 0:06:45.360 --> 0:06:47.800 the scientific warning, or you mean the science itself, the 0:06:47.880 --> 0:06:51.479 social response to the scientific warning that's in the movie. Yeah, 0:06:51.520 --> 0:06:53.719 that was pretty sobering. Actually, I think that was mostly 0:06:53.720 --> 0:06:55.640 the point of the movie. The actual science a bit 0:06:55.640 --> 0:06:58.000 where they're like at the white board figuring out the 0:06:58.040 --> 0:07:00.280 trajectory of the comment. That was like the first two 0:07:00.279 --> 0:07:02.799 minutes of the movie. After that, there was a great 0:07:02.920 --> 0:07:05.920 much science, But that part was pretty accurate. You know though, 0:07:05.960 --> 0:07:08.000 I heard that they had to find somebody to play 0:07:08.040 --> 0:07:11.240 a math double for Leonardo DiCaprio. When they zoom in 0:07:11.280 --> 0:07:14.560 on the whiteboard, that's not actually his hand doing those calculations, 0:07:15.080 --> 0:07:17.920 which means there's a whole other career. I didn't even 0:07:17.960 --> 0:07:21.440 realize I was missing out on, you know, Hollywood math double. 0:07:21.640 --> 0:07:23.440 Who do you think you would be in terms of 0:07:23.480 --> 0:07:28.200 Hollywood's math double. I'd like to be Jeff Goldblum's math double. 0:07:28.800 --> 0:07:30.760 I want to do his math. Jeff, if you're listening, 0:07:30.840 --> 0:07:33.120 please hooking me up. I don't want you to hurt 0:07:33.160 --> 0:07:35.360 yourself doing maths, so please let me take the fall 0:07:35.400 --> 0:07:39.400 for you. But speaking of taking the falls, some of 0:07:39.440 --> 0:07:42.280 these comets that enter the Solar System are pretty small. 0:07:42.320 --> 0:07:44.640 There's just a few kilometers wide. But there's some been 0:07:44.720 --> 0:07:48.720 some recent discoveries that are stretching people's brains about how 0:07:48.880 --> 0:07:53.920 big a comet can be. So you're saying that asteroids 0:07:54.080 --> 0:07:59.120 are not typically that dangerous whereas comets are. Why is 0:07:59.160 --> 0:08:01.720 that is that base stun the stuff that they're made 0:08:01.760 --> 0:08:05.000 out of, or their behaviors. It's mostly based on our 0:08:05.040 --> 0:08:08.560 ability to see them. Commets orbit in the Inner Solar System, 0:08:08.680 --> 0:08:10.640 and so we can point our telescopes and we can 0:08:10.640 --> 0:08:12.880 watch them, and we can see where they're going, and 0:08:12.920 --> 0:08:15.280 we are not worried about them because we know where 0:08:15.280 --> 0:08:18.200 basically all the big ones are. They reflect enough sunlight 0:08:18.280 --> 0:08:20.640 for us to track them and predict their path for 0:08:20.680 --> 0:08:23.280 a few hundred years. Once it astronomer gets like four 0:08:23.360 --> 0:08:26.640 or five six measurements of the motion of an object, 0:08:26.680 --> 0:08:30.040 they can pretty well predict its path. But comets have 0:08:30.280 --> 0:08:33.080 very long periods. Some of these things have like hundreds 0:08:33.200 --> 0:08:36.120 or thousands of years long period, which means the first 0:08:36.160 --> 0:08:39.160 time we see it might be when it's headed towards 0:08:39.200 --> 0:08:41.400 the Earth, which is why you might not get a 0:08:41.440 --> 0:08:44.720 whole lot of warning. And they're going much much faster 0:08:44.840 --> 0:08:47.959 because they're falling in from much further away. And those 0:08:48.000 --> 0:08:50.000 of you who watch these guys might remember that this 0:08:50.120 --> 0:08:54.560 happened in This is not just fiction. In comment entered 0:08:54.559 --> 0:08:58.000 the Solar System and then smacked right into Jupiter. It 0:08:58.080 --> 0:09:00.760 was spectacular. You could see it with your own telescope 0:09:00.760 --> 0:09:03.640 in your own backyard, earth size fireballs rising from the 0:09:03.679 --> 0:09:06.800 surface of Jupiter. It was like astronomical schadenfreud. You know, 0:09:06.840 --> 0:09:09.280 it's pretty awesome, but we were glad it wasn't hitting us. 0:09:09.400 --> 0:09:19.480 Those poor Jupidtonians Jupidonians having to have that name. Man, 0:09:19.559 --> 0:09:21.200 we'll have to ask or hey, what he would prefer 0:09:21.240 --> 0:09:23.640 as a name of that. It's definitely not jupiter Lyns. 0:09:23.760 --> 0:09:29.120 That would be pretty awkward Jupeians. Maybe a much bit Cans, 0:09:30.520 --> 0:09:35.480 my fellow Jupidicns. We can't necessarily know when a comment 0:09:35.720 --> 0:09:39.800 is coming, but should we really be that worried? Our 0:09:39.840 --> 0:09:43.080 atmosphere is pretty hot, so it seems like it could 0:09:43.440 --> 0:09:46.160 melt a comment, right. Our atmosphere is pretty hot, and 0:09:46.240 --> 0:09:48.840 you can melt a comment if it wasn't too big. 0:09:48.960 --> 0:09:52.240 But remember the impactory that took out the dinosaurs million 0:09:52.320 --> 0:09:56.120 years ago was only a few kilometers wide, So anything 0:09:56.160 --> 0:09:58.080 bigger than that is going to make it to the 0:09:58.080 --> 0:10:01.040 surface of the Earth and deposit a lot of kinetic energy. 0:10:01.200 --> 0:10:03.200 And so that's why it's really important to think about 0:10:03.280 --> 0:10:07.040 questions like, well, how big can a comment get? And 0:10:07.080 --> 0:10:10.080 so today in the podcast will be asking that exact question, 0:10:15.080 --> 0:10:21.240 how big can a comment get? Um Empire State building size? 0:10:21.320 --> 0:10:24.080 That's that's my guest. You just like the mental visual 0:10:24.440 --> 0:10:28.439 of the Empire state building crashing into the earth. Somebody's 0:10:28.440 --> 0:10:31.160 got to do that in Hollywood. Maybe blue whale size, 0:10:31.200 --> 0:10:33.560 because I also like the image of a blue whale 0:10:33.600 --> 0:10:36.920 crashing in Earth. Man talk about a belly flop, right, 0:10:36.960 --> 0:10:40.160 a blue whale coming from space and hitting the ocean. Ouch, 0:10:40.360 --> 0:10:42.800 that sounds like it hurts well as usual. I was 0:10:42.880 --> 0:10:45.480 curious what people out there in the Internet thought about 0:10:45.520 --> 0:10:48.240 this question. Have people thought about how big a commt is? 0:10:48.360 --> 0:10:51.000 Do they have any idea how large these snowballs from 0:10:51.040 --> 0:10:53.720 the far reaches of space can be? So I asked 0:10:53.720 --> 0:10:57.360 folks to volunteer to answer random physics questions to contribute 0:10:57.360 --> 0:11:00.280 to the podcast. And if you would like to participate, lease, 0:11:00.360 --> 0:11:03.479 don't be shy. You are very very welcome. No expertise 0:11:03.600 --> 0:11:06.920 is required. Just email me two questions at Daniel and 0:11:07.040 --> 0:11:10.200 Jorge dot com. So before you listen to these answers, 0:11:10.240 --> 0:11:13.000 think to yourself, how big do you think a comet 0:11:13.120 --> 0:11:16.960 can get here's what people had to say, pretty big. 0:11:17.200 --> 0:11:19.920 But then it starts getting into like whether you classify 0:11:19.960 --> 0:11:23.040 as common or a planet. I think comments can get 0:11:23.120 --> 0:11:25.960 as big as some of the largest planets out there. 0:11:26.120 --> 0:11:30.320 I think if something happens where planet gets out of 0:11:30.520 --> 0:11:36.800 orbit or start pades away, um, then those planets could 0:11:36.840 --> 0:11:41.480 then become free. Practically, I never thought that comments could 0:11:42.440 --> 0:11:45.000 or like pigeonholed into a certain size. I think, you know, 0:11:45.080 --> 0:11:47.559 it could just be a stray ice ball. But size 0:11:47.600 --> 0:11:53.240 doesn't really matter for comments. Well, based purely on imagination, 0:11:54.040 --> 0:11:58.120 I think comments can get as big as our moon. 0:11:58.520 --> 0:12:00.880 I ventured to guess comments can become as large as 0:12:00.880 --> 0:12:03.920 they can until they are too large to be called commets. 0:12:04.240 --> 0:12:08.760 From what I know, commets are this frozen stuff of 0:12:09.000 --> 0:12:15.440 dust and solids and gases. So it depends on what 0:12:15.640 --> 0:12:19.560 the commet has in it, because most of the stuff 0:12:19.600 --> 0:12:24.440 gets melted away as it enters and becomes warmer and hotter. 0:12:25.320 --> 0:12:28.560 What would prevent a comment from getting too big? I 0:12:28.600 --> 0:12:31.240 guess the two things that I can think of our 0:12:31.800 --> 0:12:34.719 If it's too big, it could break up easily, and 0:12:34.760 --> 0:12:37.160 hence you won't have one comment, you'll have multiple comments, 0:12:37.200 --> 0:12:40.439 and that's related to the structure of it. The other 0:12:40.480 --> 0:12:43.920 thing is that if you have something that's very big, 0:12:44.120 --> 0:12:48.280 it's likely not made out of a large percentage of 0:12:48.280 --> 0:12:50.840 ice crystals, is probably going to be highly metallic and 0:12:51.000 --> 0:12:54.000 won't develop the tails of the comments. So that still 0:12:54.040 --> 0:12:56.760 doesn't answer the question of how big can the comment get. 0:12:56.800 --> 0:13:00.160 I would guess I don't know, three or four or 0:13:00.200 --> 0:13:05.439 bus sizes. I don't know. I would imagine it will 0:13:05.520 --> 0:13:09.880 get as big as it can without the dust squishing it, 0:13:09.920 --> 0:13:14.520 because aren't commits quite low density. I suppose the gravity 0:13:14.600 --> 0:13:18.080 might turn it into an asteroid. I'm not sure about 0:13:18.080 --> 0:13:22.360 what the definitions are there, but I hope that's helped 0:13:22.400 --> 0:13:26.920 in some way. That's a good question. I imagine they 0:13:26.960 --> 0:13:34.000 could get bigger than an asteroid, depending on how much 0:13:34.240 --> 0:13:38.080 gravity maybe they had when they were out far far 0:13:38.280 --> 0:13:41.040 far in the far reaches of the solar systems or 0:13:41.040 --> 0:13:45.120 the orc clouds, or wherever they get all their ice from. Like, 0:13:45.240 --> 0:13:49.800 maybe they're just a particularly big chunk that gathered a 0:13:49.840 --> 0:13:54.240 whole lot and solidified before it came rushing in towards 0:13:54.400 --> 0:13:57.840 the center of our solar system. All right, so nobody 0:13:57.840 --> 0:14:02.040 else that empire states building or whale sized. Well, I 0:14:02.080 --> 0:14:05.880 am interested in the question of when does it become 0:14:05.880 --> 0:14:09.199 a planet. Is the only thing separating something like a 0:14:09.200 --> 0:14:12.360 comet and a planet just its signs? Or is there 0:14:12.400 --> 0:14:16.080 some other property to a comet that makes it not 0:14:16.200 --> 0:14:19.520 a planet? Oh man, this is such a tangle of names. 0:14:19.840 --> 0:14:23.080 The astronomers have made such a mess of what they 0:14:23.120 --> 0:14:25.600 call things. Is it a centaur, is it a trans 0:14:25.600 --> 0:14:28.720 Newtonian object? It is a minor planet. There are such 0:14:28.880 --> 0:14:32.720 ridiculous and sometimes conflicting rules about these things. In this case, 0:14:32.760 --> 0:14:35.800 you can actually make a nice little line between what's 0:14:35.800 --> 0:14:38.320 a comet and what's not. What you call a comet 0:14:38.520 --> 0:14:42.160 is something that has an atmosphere because the Sun is 0:14:42.240 --> 0:14:45.320 heating it up and it's out gassing. So imagine some 0:14:45.520 --> 0:14:48.720 icy ball thousands of au away from the Sun. It's 0:14:48.720 --> 0:14:50.520 just going to be sitting there frozen. But if it 0:14:50.560 --> 0:14:53.240 falls in towards the Solar System and the Sun starts 0:14:53.280 --> 0:14:55.800 to heat it up, then some of those ices are 0:14:55.800 --> 0:14:57.520 going to turn into gas, and they're going to give 0:14:57.560 --> 0:14:59.840 that comet a little atmosphere, which they call a co 0:15:00.280 --> 0:15:01.960 and it might even give it a little tail if 0:15:01.960 --> 0:15:04.280 some of it is blown off behind it. So that's 0:15:04.280 --> 0:15:07.800 what distinguishes an asteroid from a comet or a planet, 0:15:07.920 --> 0:15:11.240 or even a minor planet, or a or trans neptunity sorry, 0:15:11.240 --> 0:15:16.080 trans Neptunian objects, not trans Newtonian. Nobody launched isamutany into 0:15:16.080 --> 0:15:20.880 outer space yet they should have, though, that would teach 0:15:20.920 --> 0:15:24.120 him a thing or two about gravity. So if these 0:15:24.200 --> 0:15:29.000 comets have atmospheres, could this mean that some form of 0:15:29.120 --> 0:15:32.360 life could conceivably breathe it in or is it just 0:15:32.560 --> 0:15:36.000 inherently unfriendly towards life? Oh, I was hoping you were 0:15:36.000 --> 0:15:38.240 going to go there, the biologist, and you can't resist 0:15:38.280 --> 0:15:42.040 asking that question. Now, of course, we can never say never, 0:15:42.240 --> 0:15:44.960 because life is weird and could take all sorts of 0:15:44.960 --> 0:15:48.640 strange forms. But these would be very short lived atmospheres. 0:15:49.000 --> 0:15:51.520 This is something that doesn't exist when it's out there, 0:15:51.560 --> 0:15:54.640 deep into space. It only appears when the comet is 0:15:54.680 --> 0:15:59.560 falling towards the Sun and it's not gravitationally bound like 0:15:59.640 --> 0:16:02.080 these things are not big enough to have an atmosphere. 0:16:02.280 --> 0:16:05.000 The reason an asteroid doesn't have an atmosphere is that 0:16:05.040 --> 0:16:07.440 doesn't have enough gravity to hold onto it. Even the 0:16:07.480 --> 0:16:10.440 Moon doesn't have enough gravity to hold onto it. If 0:16:10.440 --> 0:16:13.080 you like pumped an atmosphere onto the moon. We all 0:16:13.120 --> 0:16:15.200 just drift away in a few dozen years or maybe 0:16:15.200 --> 0:16:18.360 a hundred. So a commet, it's atmosphere sort of transient. 0:16:18.640 --> 0:16:20.880 It keeps losing it and then it keeps replenishing it 0:16:20.920 --> 0:16:23.480 by outgassing it. So it'd be pretty hard situation, I 0:16:23.480 --> 0:16:26.840 think for life to form. So you'd basically just get 0:16:26.920 --> 0:16:31.400 a few puffs of atmosphere as life, but you wouldn't 0:16:31.440 --> 0:16:36.600 have millions of years to evolve. On this comment more 0:16:36.640 --> 0:16:39.920 of a vape situation. If you're a life form, Yeah, 0:16:40.040 --> 0:16:42.960 unless you're something really weird form of life, which can 0:16:43.000 --> 0:16:45.360 like go into stasis for a long long time and 0:16:45.400 --> 0:16:48.080 then wake up again, like those insects that wake up 0:16:48.080 --> 0:16:51.080 every seventeen years and like take a few breaths, live 0:16:51.120 --> 0:16:53.560 a very short life as the common is diving towards 0:16:53.640 --> 0:16:55.480 the sun, and then go back to sleep. Well, you know, 0:16:55.560 --> 0:16:58.480 there is a life form already out in space that 0:16:58.680 --> 0:17:03.600 can go into stays us and can survive the rigors 0:17:03.680 --> 0:17:07.280 of the vacuum of space at least for short periods 0:17:07.280 --> 0:17:10.280 of time, and those are tartar grades. So who knows, 0:17:10.640 --> 0:17:13.760 maybe some of those tartar grades we accidentally dropped on 0:17:13.800 --> 0:17:17.399 the moon, will someday find their way to sort of 0:17:17.520 --> 0:17:20.800 ride a comet for a little while. You think maybe 0:17:20.800 --> 0:17:23.640 they're gonna just like jump off the moon because there's 0:17:23.680 --> 0:17:26.119 such a little gravity there, land on a comet and 0:17:26.200 --> 0:17:28.639 ride it around the Solar system. That sounds pretty awesome, 0:17:28.680 --> 0:17:37.240 like doctor Strange love Tartar Grade, little tiny silver surfers. Well, 0:17:37.280 --> 0:17:39.919 that sounds like a great science fiction novel. So what 0:17:40.040 --> 0:17:43.000 we're talking about today are these comets, and these comments 0:17:43.000 --> 0:17:46.040 are again distinguished from asteroids because they have a coma 0:17:46.200 --> 0:17:48.359 and they can have a tail. A tail is not 0:17:48.400 --> 0:17:50.600 actually necessary for it to be a comet. A lot 0:17:50.640 --> 0:17:53.320 of people think about comments. They think about tails because 0:17:53.320 --> 0:17:55.159 when you look up in the sky, that's how a 0:17:55.160 --> 0:17:57.800 comet looks different from just like a star or something 0:17:57.800 --> 0:18:01.440 else shiny. Technically, though, astronom will call it a comet 0:18:01.960 --> 0:18:04.359 even if it doesn't yet have a tail, like before 0:18:04.400 --> 0:18:07.200 it's really fallen into the inner Solar system, it can 0:18:07.240 --> 0:18:09.720 still just have a coma. The other weird thing about 0:18:09.720 --> 0:18:12.679 comets is that they don't always just have one tail. 0:18:13.040 --> 0:18:18.600 They can have two different tails simultaneously, so just kind 0:18:18.600 --> 0:18:21.359 of a split stream going on or these tails made 0:18:21.400 --> 0:18:23.960 out of different stuff, so comments on that, like these 0:18:24.000 --> 0:18:26.600 dirty snowballs, and some of the stuff when he gets 0:18:26.640 --> 0:18:29.640 heated up, turns into gas and then the sun blows 0:18:29.720 --> 0:18:32.000 that away. So one of the tails of a comet 0:18:32.080 --> 0:18:35.200 is a gas tail, and that's pointing away from the sun. 0:18:35.640 --> 0:18:37.760 A lot of people think like the comets tail is 0:18:37.800 --> 0:18:40.919 pointing behind it, sort of like a rocket's exhaust or 0:18:41.000 --> 0:18:43.280 like you know those wiggle motions in a cartoon. That 0:18:43.320 --> 0:18:45.879 means that something is moving fast, but it's actually pointing 0:18:45.920 --> 0:18:48.679 away from the sun, like the sun is blowing gas 0:18:48.720 --> 0:18:51.280 away from it. So that's the gas tail. The other 0:18:51.359 --> 0:18:53.720 tail is typically made out of dust to like little 0:18:53.720 --> 0:18:56.399 bits of rock or whatever from the core of a comet, 0:18:56.480 --> 0:18:58.879 the non ice parts, and those are a little heavier 0:18:58.920 --> 0:19:00.800 so they don't get blown by the solar wind and 0:19:00.840 --> 0:19:03.600 they do actually follow more like the trajectory of the comet. 0:19:03.880 --> 0:19:06.080 So you have one tail that's sort of flying out 0:19:06.119 --> 0:19:08.840 behind the comet along its path and the other one 0:19:08.920 --> 0:19:11.280 that's getting blown away by the sun. And these are 0:19:11.320 --> 0:19:13.480 not always pointed in the same direction. So if you're 0:19:13.520 --> 0:19:15.919 really lucky, you can see a comet with both of 0:19:15.960 --> 0:19:19.600 these tails. Simultaneously, it looks pretty spectacular. So for thinking 0:19:19.840 --> 0:19:24.000 of a comet like a runway model, the gas tail 0:19:24.320 --> 0:19:27.800 is its hair getting blown out of its face by 0:19:27.880 --> 0:19:33.080 some conveniently placed fans, and the dust tail is like 0:19:33.160 --> 0:19:36.720 it's cloak, kind of wafting behind it as it struts 0:19:36.760 --> 0:19:39.840 down the runway, hopefully not towards Earth exactly. And if 0:19:39.840 --> 0:19:42.639 you are running with a tail wind right when the 0:19:42.680 --> 0:19:45.080 comet comes around the Sun and it's now going back 0:19:45.119 --> 0:19:48.280 into the outer Solar System, then its tail is pointing 0:19:48.400 --> 0:19:51.040 in the direction it's moving. It's like an anti tail 0:19:51.119 --> 0:19:53.280 because the Sun is now behind it, and so it's 0:19:53.320 --> 0:19:56.280 blowing gas in the direction the comet is moving. So 0:19:56.320 --> 0:19:59.280 the tail isn't always even behind the comet. Sometimes it's 0:19:59.280 --> 0:20:02.720 ahead of comment. So if we see a giant comet 0:20:03.160 --> 0:20:06.080 that has a tail pointed in our direction, that does 0:20:06.119 --> 0:20:08.719 not mean we're not in danger, because it could be 0:20:08.800 --> 0:20:11.800 coming right this way. That's right. You need me at 0:20:11.840 --> 0:20:14.760 the white board or somebody else doing those calculations before 0:20:14.800 --> 0:20:17.000 you know whether or not we should abandon the planet. 0:20:17.119 --> 0:20:19.520 And these comments come into different groups. Some of them 0:20:19.560 --> 0:20:22.960 are short period comets which come from the Piper Belt. 0:20:23.320 --> 0:20:26.480 This is a region of just like icy stuff. Planetism 0:20:26.520 --> 0:20:29.320 as just past Neptune, you know, past Neptune. This like 0:20:29.359 --> 0:20:32.840 a whole, big, messy pile of stuff. That's why people 0:20:32.960 --> 0:20:35.960 argue about whether Pluto should be a planet, because Pluto 0:20:36.040 --> 0:20:37.960 is the first thing we saw out there that was 0:20:37.960 --> 0:20:40.359 about that size, and then we discovered, oh my gosh, 0:20:40.520 --> 0:20:42.920 there's a lot of these like frozen balls out there. 0:20:42.960 --> 0:20:45.959 There are about Pluto size. We call Pluto a planet, 0:20:46.040 --> 0:20:49.440 we've got to call them all planets. So like after Neptune, 0:20:49.440 --> 0:20:52.560 the solar systems basically just a big mess. Sounds like 0:20:52.600 --> 0:20:55.800 a lot of planetary gate keeping. Just because Pluto's a 0:20:55.840 --> 0:20:58.400 mess doesn't mean it shouldn't be a planet. It's not 0:20:58.440 --> 0:21:00.360 just that Pluto is a mess. It's Pluto, and it's 0:21:00.400 --> 0:21:02.920 like seventeen thousand friends are all a mess, And do 0:21:02.960 --> 0:21:05.600 you want a solar system with seventeen thousand planets in it? 0:21:05.640 --> 0:21:07.240 You know, I guess it just depends on way to 0:21:07.280 --> 0:21:08.879 think of a solar system. But you know, to me, 0:21:08.960 --> 0:21:11.840 these arguments are just about names gues. It depends on 0:21:11.880 --> 0:21:14.160 if they're bringing pizza money or if they're just coming 0:21:14.160 --> 0:21:17.920 there for the free food. That's right. Anybody who brings 0:21:17.960 --> 0:21:21.080 gelato is welcome. But some of these little icy balls 0:21:21.160 --> 0:21:24.040 out there and the Kuiper Belt can get nudged and 0:21:24.160 --> 0:21:26.760 fall into the Solar System. And these are called short 0:21:26.800 --> 0:21:29.919 period comets, meaning that they take months or years to 0:21:30.000 --> 0:21:32.920 go around the Solar System. But there's another group, these 0:21:33.080 --> 0:21:36.840 long period comets that come from another source that much 0:21:36.960 --> 0:21:41.360 further out passed even the Kuiper Belt way past Pluto, 0:21:41.520 --> 0:21:44.800 many many, many thousands and millions of kilometers, and that 0:21:44.840 --> 0:21:47.920 comes from this blob called the Oort Cloud, which is 0:21:48.040 --> 0:21:51.760 this theoretical cloud of icy many planets. And I say 0:21:51.800 --> 0:21:54.960 theoretical because we're pretty sure it's there, but we've never 0:21:55.119 --> 0:21:59.360 actually seen it, so we only know about it's possible 0:21:59.400 --> 0:22:04.080 existence based on the garbage that it throws our way exactly. 0:22:04.240 --> 0:22:08.000 We can't otherwise explain where these comments come from. And 0:22:08.119 --> 0:22:11.400 so based on these comments about fifty years ago, Yon 0:22:11.600 --> 0:22:15.280 Ord suggested maybe there's this huge group of icy balls 0:22:15.320 --> 0:22:18.160