WEBVTT 1 00:00:03.399 --> 00:00:07.719 Welcome to Bedtime Astronomy. Explore the wonders of the cosmos 2 00:00:07.759 --> 00:00:12.279 with our soothing Bedtime Astronomie podcast. Each episode offers a 3 00:00:12.359 --> 00:00:16.320 gentle journey through the stars, planets, and beyond, perfect for 4 00:00:16.399 --> 00:00:20.239 unwinding after a long day. Let's travel through the mysteries 5 00:00:20.239 --> 00:00:22.440 of the universe as you drift off into a peaceful 6 00:00:22.480 --> 00:00:23.800 slumber under the night sky. 7 00:00:26.920 --> 00:00:29.960 I want you to just take a second, close your 8 00:00:30.000 --> 00:00:34.359 eyes maybe, and think about our moon, Luna, how absolutely 9 00:00:34.399 --> 00:00:37.240 vile it is. It's just it's so big, so close, 10 00:00:37.280 --> 00:00:39.399 it feels fundamental. You know, we kind of take it 11 00:00:39.479 --> 00:00:41.679 for granted. We see the tide, sure, we see the moonlight, 12 00:00:41.960 --> 00:00:44.320 but do we really stop to think that if Earth 13 00:00:44.359 --> 00:00:48.719 hadn't captured that giant companion way back when life like us, complex, 14 00:00:48.840 --> 00:00:52.280 long lived life, it might never have even gotten started. Seriously, 15 00:00:52.479 --> 00:00:55.560 we could have been just this unstable spinning rock, wobbling 16 00:00:55.600 --> 00:00:58.240 all over the place with a crazy axial tilt, no 17 00:00:58.359 --> 00:01:02.359 stable climate, no chance. And that thought brings us right 18 00:01:02.399 --> 00:01:04.480 into this huge paradox. In our search for life out there, 19 00:01:04.560 --> 00:01:08.400 we found thousands of exoplanets, thousands, the galaxy seems packed 20 00:01:08.439 --> 00:01:11.519 with them, But exo moons where are they? Logically they 21 00:01:11.519 --> 00:01:14.920 have to be out there, right. We have zero confirmed ones, none, 22 00:01:15.120 --> 00:01:17.640 just maybe a couple of interesting candidates that we're still 23 00:01:17.640 --> 00:01:20.959 squinting at. Finding them is tough, really tough. So astronomers 24 00:01:21.000 --> 00:01:24.000 have been focusing on where moons might matter most for habitability, 25 00:01:24.280 --> 00:01:25.920 and for a long time that meant looking at planets 26 00:01:25.920 --> 00:01:28.519 around m dwarfs, you know, the old red dwarf stars. 27 00:01:28.640 --> 00:01:30.359 They make up most of the stars in the galaxy. 28 00:01:30.799 --> 00:01:33.840 But it turns out the physics in those systems it 29 00:01:33.920 --> 00:01:37.840 might be incredibly harsh, really destructive. So today we're diving 30 00:01:37.840 --> 00:01:40.480 into some fascinating new research. It's led by Sean Patel 31 00:01:40.519 --> 00:01:43.040 and the paper's title really says it all tidally torn 32 00:01:43.319 --> 00:01:46.760 why the most common stars may lack large habitable zone moons. 33 00:01:47.439 --> 00:01:51.359 We're going to unpack the well terrifying orbital mechanics of 34 00:01:51.359 --> 00:01:53.480 these red dwarf systems and find out why the very 35 00:01:53.480 --> 00:01:55.920 conditions that might seem good for life could actually be destroying. 36 00:01:55.959 --> 00:01:59.200 The moon's life might need to hang on long term. Okay, 37 00:01:59.200 --> 00:02:01.480 so let's get into this. Is it possible that the 38 00:02:01.480 --> 00:02:05.599 most commonplaces for planets in the galaxy are just moonless 39 00:02:06.359 --> 00:02:08.000 or at least lack the big moons. What does that 40 00:02:08.039 --> 00:02:09.080 mean for finding another Earth. 41 00:02:09.159 --> 00:02:12.400 It's a really pivotal question right now in astrobiology, absolutely, 42 00:02:12.960 --> 00:02:16.400 because we use the Earth Moon system as our benchmark, 43 00:02:16.560 --> 00:02:19.560 our sort of end of one example for a habitable world. 44 00:02:19.840 --> 00:02:23.520 And when you compare our moon Luna to basically any 45 00:02:23.560 --> 00:02:27.000 other moon in our own solar system, the difference is 46 00:02:27.120 --> 00:02:31.120 just striking. Relative to Earth's size, Our moon is enormous. 47 00:02:31.159 --> 00:02:34.280 That mass ratio planet to moon, it's way off the 48 00:02:34.400 --> 00:02:38.560 charts compared to Jupiter's moons or Saturns. And that sheer size, 49 00:02:38.599 --> 00:02:41.159 that's where it's incredible stabilizing power comes from. 50 00:02:41.280 --> 00:02:43.159 Right, It's not just a pretty nihild. It's doing heavy 51 00:02:43.240 --> 00:02:44.840 lifting gravitationally. 52 00:02:44.240 --> 00:02:45.120 Speaking, exactly. 53 00:02:45.599 --> 00:02:49.280 The scientific consensus really is that without Luna Earth's history, 54 00:02:49.520 --> 00:02:53.360 Life's history would look fundamentally different if life even got 55 00:02:53.400 --> 00:02:55.240 going in the first place, which is a big if. 56 00:02:55.520 --> 00:02:57.400 We can kind of break down its key jobs for 57 00:02:57.439 --> 00:03:00.879 habitability into two main things, and we need to grasp 58 00:03:01.000 --> 00:03:03.319 both to really see what might be missing around those 59 00:03:03.400 --> 00:03:03.919 m dwarfs. 60 00:03:04.000 --> 00:03:05.520 Okay, let's start with a big one, the one that 61 00:03:05.560 --> 00:03:09.560 gives us stable climates over long, long periods, axeal tilt stability. 62 00:03:09.840 --> 00:03:14.159 Yes, first up is axeal stability. Earth tilts on its 63 00:03:14.199 --> 00:03:17.039 axis about twenty three point five degrees right now. That 64 00:03:17.120 --> 00:03:20.879 gives us our regular seasons, predictable climate zones. Our moon 65 00:03:21.120 --> 00:03:25.000 acts like this giant gravitational gyroscope. Basically it keeps that 66 00:03:25.080 --> 00:03:28.520 tilt the planet's obliquity from swinging wildly over millions, even 67 00:03:28.599 --> 00:03:31.879 billions of years without that big moon acting as an anchor. 68 00:03:32.199 --> 00:03:36.240 Models suggest Earth's tilt could wobble chaotically, maybe from like 69 00:03:36.759 --> 00:03:38.719 zero degrees so no seasons at all, all the way 70 00:03:38.800 --> 00:03:41.400 up to eighty five degrees where the poles are practically 71 00:03:41.439 --> 00:03:42.360 pointing straight. 72 00:03:42.120 --> 00:03:42.560 At the sun. 73 00:03:43.039 --> 00:03:46.000 WHOA, okay, eighty five degrees. What happens to a planet 74 00:03:46.039 --> 00:03:48.039 if its axis is swinging around like that? What are 75 00:03:48.039 --> 00:03:48.800 the consequences? 76 00:03:49.000 --> 00:03:51.639 Uh? Cataclysmic is probably the right word. The climate shifts 77 00:03:51.639 --> 00:03:54.199 would be extreme. If the tilt gets too low, close 78 00:03:54.240 --> 00:03:57.560 to zero, the poles stay freezing, cold, ice cacs grow huge. 79 00:03:57.840 --> 00:04:00.639 Maybe you trigger a runaway snowball Earth scenario. But if 80 00:04:00.639 --> 00:04:03.080 it swings the other way, it's really extreme. You could 81 00:04:03.080 --> 00:04:06.840 get these incredibly rapid violent climate swings, cycles of oceans 82 00:04:06.879 --> 00:04:09.560 potentially boiling near the equator and then global deep freezes. 83 00:04:09.599 --> 00:04:12.280 Yeah, trying to evolve anything more complix than maybe some 84 00:04:12.360 --> 00:04:16.079 hardy microbes in that kind of environment, Yeah, it sounds impossible. 85 00:04:16.360 --> 00:04:19.720 It's hard to imagine. The Moon essentially gives us billions 86 00:04:19.720 --> 00:04:24.120 of years of relative climate stability. That consistent seasonality is 87 00:04:24.120 --> 00:04:27.959 probably crucial for complex life to emerge, diversify, and thrive. 88 00:04:28.680 --> 00:04:30.800 You just have to look at Mars. It only has 89 00:04:30.879 --> 00:04:34.279 these tiny little moons, Phobos and demos. They do basically 90 00:04:34.319 --> 00:04:38.199 nothing for stability. And Mars's axial tilt it's known to 91 00:04:38.240 --> 00:04:40.720 have shifted dramatically over geological time. 92 00:04:40.839 --> 00:04:44.160 Okay, so that's the climate regulation, billions of years of stability. 93 00:04:44.399 --> 00:04:47.439 What's the second critical function, the one we see every day. 94 00:04:47.759 --> 00:04:51.079 That's the more immediate biological driver. 95 00:04:51.399 --> 00:04:52.040 Tidal action. 96 00:04:52.279 --> 00:04:55.319 The Moon pulls on Earth's oceans, creating the tides, and 97 00:04:55.360 --> 00:04:58.800 this has really profound biological effects, especially thinking about early 98 00:04:58.879 --> 00:05:00.959 life and the transition for from water to land, or 99 00:05:00.959 --> 00:05:04.120 it's complexity in general. Those zones that get repeatedly covered 100 00:05:04.120 --> 00:05:07.720 and uncovered by water, the intertidal zones, they're incredible mixing 101 00:05:07.759 --> 00:05:10.800 bowls for nutrients. They constantly expose life forms to both 102 00:05:10.839 --> 00:05:13.639 water and air, driving really important adaptations. 103 00:05:13.639 --> 00:05:17.240 Early on, I remember reading about that. Some theories suggest 104 00:05:17.319 --> 00:05:20.839 tidal pools or these area cycle by tides, or maybe 105 00:05:20.920 --> 00:05:24.040 key for concentrating the building blocks of life, the organic 106 00:05:24.079 --> 00:05:27.399 molecules needed to kick things off. So it's not just biodiversity. 107 00:05:27.480 --> 00:05:29.720 Later on, it could be about the origin itself. 108 00:05:29.800 --> 00:05:32.680 Absolutely, there's a strong case to be made there. The 109 00:05:32.800 --> 00:05:35.920 tides dump enormous amounts of mechanical energy into the oceans 110 00:05:35.959 --> 00:05:39.040 and coastal areas. They stir things up. So whether life 111 00:05:39.040 --> 00:05:41.879 got its start near deep sea hydrothermal vents or in 112 00:05:41.959 --> 00:05:45.839 shallow sunlit pools, that constant mixing and movement driven by 113 00:05:45.839 --> 00:05:48.720 the moon is likely a critical factor, which is why 114 00:05:48.839 --> 00:05:51.720 when astronomers are looking out at other star systems, just 115 00:05:51.759 --> 00:05:55.040 finding a rocky planet in the habitable zone, well. 116 00:05:54.800 --> 00:05:55.800 It might not be enough. 117 00:05:56.319 --> 00:05:59.720 We really need to find systems that also have these big, stabilizing, 118 00:06:00.040 --> 00:06:01.560 potentially life stirring moons. 119 00:06:01.879 --> 00:06:04.879 And this isn't just a fringe idea, right The search 120 00:06:04.879 --> 00:06:08.079 for exomoons is becoming pretty mainstream in the astronomy community. 121 00:06:08.240 --> 00:06:08.959 They see the need. 122 00:06:09.160 --> 00:06:13.319 Oh, definitely, it's moved from theoretical wish lists, right into 123 00:06:13.480 --> 00:06:17.319 actual observing plans for our best telescopes, I mean prime 124 00:06:17.360 --> 00:06:21.240 observing time on the James webspased telescope JAWST has been 125 00:06:21.240 --> 00:06:23.720 specifically allocated to hunt for an exomoon. 126 00:06:23.959 --> 00:06:25.920 Really, which system are they looking at? 127 00:06:26.079 --> 00:06:29.319 They're targeting a planet called TOI seven hundred D. It's 128 00:06:29.360 --> 00:06:31.480 a rocky world, looks like it's smack in the middle 129 00:06:31.519 --> 00:06:35.360 of its stars habitable zone, and there are some let's say, 130 00:06:35.399 --> 00:06:39.120 intriguing hints nothing confirmed yet, but hints that it might 131 00:06:39.240 --> 00:06:41.519 host a large Luna like moon. 132 00:06:41.759 --> 00:06:44.759 Wow. So if JDABST actually confirmed a big moon there, 133 00:06:45.279 --> 00:06:46.839 that would be huge game chance. 134 00:06:46.920 --> 00:06:50.319 We'd be revolutionary overnight. Suddenly, the idea of habitable worlds 135 00:06:50.360 --> 00:06:52.480 needing moons wouldn't just be based on our one example. 136 00:06:52.480 --> 00:06:54.879 We'd have another data point. But and this is the 137 00:06:54.879 --> 00:06:57.360 big butt from the Patel research we're talking about. The 138 00:06:57.399 --> 00:07:00.319 study suggests that these very systems were most interest in 139 00:07:00.439 --> 00:07:04.000 the M dwarf systems like TOI seven hundreds might be 140 00:07:04.079 --> 00:07:06.480 fundamentally unable to keep a large moon like that for 141 00:07:06.600 --> 00:07:07.040 very long. 142 00:07:07.319 --> 00:07:12.160 Okay, let's dive into that tension. Why M dwarfs, Why 143 00:07:12.160 --> 00:07:14.959 are they both the most common places to look statistically 144 00:07:15.480 --> 00:07:19.480 and maybe the worst places for moons to survive physically. So, 145 00:07:19.639 --> 00:07:21.959 just to set the scene again, M dwarfs red dwarfs, 146 00:07:22.519 --> 00:07:26.439 small stars, cool, not very bright, but and this is key, 147 00:07:26.439 --> 00:07:28.399 they make up something like three quarters of all stars 148 00:07:28.399 --> 00:07:31.360 in the Milky Way. They're just everywhere, and we know 149 00:07:31.439 --> 00:07:34.160 from Kepler and tests and other surveys that they often 150 00:07:34.199 --> 00:07:38.319 have rocky planets orbiting them, including planets in their habitable zones. 151 00:07:38.519 --> 00:07:41.439 So purely by numbers, M dwarfs look like prime real estate. 152 00:07:41.600 --> 00:07:44.600 Statistically, yes, absolutely, if you're playing the numbers game, M 153 00:07:44.639 --> 00:07:47.079 dwarfs are where you place your bets. But the physics, 154 00:07:47.519 --> 00:07:50.319 the physics gets tricky. The biggest issue comes directly from 155 00:07:50.319 --> 00:07:53.759 them being so dim. Remember the habitable zone, the Goldilock zone. 156 00:07:53.920 --> 00:07:56.199 Its distance is said by how much heat the star 157 00:07:56.279 --> 00:07:59.399 puts out. Because En dwarfs are so faint, their habitable 158 00:07:59.439 --> 00:08:02.240 zones are in incredibly close to the star Way, way 159 00:08:02.240 --> 00:08:04.160 closer than Earth's orbit around our Sun. 160 00:08:04.240 --> 00:08:06.319 Okay, put that in perspective, how close are we talking? 161 00:08:06.439 --> 00:08:09.120 Well, if you think about Earth being at one astronomical 162 00:08:09.199 --> 00:08:13.199 unit ninety three million miles from our Sun, the habitable 163 00:08:13.279 --> 00:08:16.759 zone around a typical en dwarf might be more like uh, 164 00:08:17.439 --> 00:08:20.560 inside Mercury's orbit, maybe only a few million miles out 165 00:08:20.560 --> 00:08:22.040 from the star in some cases. 166 00:08:22.120 --> 00:08:25.560 Wow, Okay, that is close, and being that close has 167 00:08:25.800 --> 00:08:29.040 major consequences for a planet and especially for its moon. Right, 168 00:08:29.759 --> 00:08:32.240 tidal sources must be immense. 169 00:08:31.879 --> 00:08:34.639 Exactly, you get two huge tidal consequences. 170 00:08:34.720 --> 00:08:36.360 The first one we hear about a lot within boar 171 00:08:36.360 --> 00:08:39.039 of planets is tidal locking. Yeah, where the planet always 172 00:08:39.039 --> 00:08:40.440 shows the same face to the star. 173 00:08:40.799 --> 00:08:44.759 Correct, That close proximity makes it almost inevitable that the 174 00:08:44.759 --> 00:08:47.519 planet becomes tidally locked, just like our moon is locked 175 00:08:47.519 --> 00:08:50.159 to Earth. So you get one side perpetually baked by 176 00:08:50.159 --> 00:08:52.600 the star and the other side locked in permanent freezing 177 00:08:52.679 --> 00:08:56.720 night life might maybe find a niche in the terminator zone, 178 00:08:56.799 --> 00:08:59.360 that twilight ring around the edge, but that's a whole 179 00:08:59.360 --> 00:09:00.600 other challenge for habitability. 180 00:09:00.639 --> 00:09:02.960 Okay, so tidal locking of the planet is one consequence. 181 00:09:03.000 --> 00:09:05.159 What's the second, the one that's critical for this research 182 00:09:05.200 --> 00:09:05.759 about moons. 183 00:09:05.919 --> 00:09:08.720 The second consequence is the raw power of the stellar 184 00:09:08.799 --> 00:09:12.639 tides acting on the Moon. Because the habitable zone planet 185 00:09:12.679 --> 00:09:16.240 is orbiting so incredibly close to the M dwarf, the 186 00:09:16.240 --> 00:09:20.399 star zone gravity exerts this immense disruptive pull on any 187 00:09:20.440 --> 00:09:24.240 moon orbiting that planet. The star is basically in a constant, 188 00:09:24.440 --> 00:09:28.240 fierce gravitational competition with the planet trying to steal its moon. 189 00:09:28.679 --> 00:09:30.799 It really does sound like a cosmic tug of war. 190 00:09:30.960 --> 00:09:32.919 The planet's trying to hold onto its moon, but this 191 00:09:33.039 --> 00:09:35.559 huge star nearby keeps yanking on the rope. 192 00:09:35.679 --> 00:09:37.279 That's a great way to picture it. And since we 193 00:09:37.360 --> 00:09:40.360 obviously can't sit and watch this gravitational battle play out 194 00:09:40.399 --> 00:09:44.000 over billions of years in real time, we have to 195 00:09:44.039 --> 00:09:44.759 simulate it. 196 00:09:44.799 --> 00:09:47.039 Right, which brings up the question, how do you even 197 00:09:47.080 --> 00:09:50.679 model that three massive object star, planet, moon, all pulling 198 00:09:50.679 --> 00:09:54.440 on each other plus tides. It sounds computationally intense. 199 00:09:54.639 --> 00:09:58.120 Oh, it is immensely so simple two body gravity, like 200 00:09:58.240 --> 00:10:00.840 just a planet and a star, planet and a moon. 201 00:10:00.879 --> 00:10:03.919 That's relatively straightforward. We have nice equations for that. But 202 00:10:04.000 --> 00:10:06.840 add that third body, the star pulling on the Moon, 203 00:10:06.919 --> 00:10:10.080 the moon pulling on the star, everything interacting. It blows 204 00:10:10.159 --> 00:10:13.240 up into the classic three body problem. There's generally no 205 00:10:13.559 --> 00:10:16.720 neat simple mathematical solution you can just write down. 206 00:10:17.039 --> 00:10:19.960 So no easy formula. How do they figure out if 207 00:10:19.960 --> 00:10:22.279 the moon stays or goes and for how long. 208 00:10:22.519 --> 00:10:24.679 The only practical way is through what are called n 209 00:10:24.759 --> 00:10:28.919 body simulations. It's a numerical technique. Basically, you telecomputer the 210 00:10:28.960 --> 00:10:32.480 initial positions and velocities of the star, planet and moon. 211 00:10:33.240 --> 00:10:37.320 Then the simulation calculates the gravitational force every object exerts 212 00:10:37.360 --> 00:10:40.000 on every other object over a tiny little timestep, maybe 213 00:10:40.039 --> 00:10:43.000 just minutes of simulated time. It figures out how those 214 00:10:43.039 --> 00:10:45.960 forces change their paths, moves them to their new positions, 215 00:10:46.039 --> 00:10:49.759 and then it repeats again and again for millions or 216 00:10:49.799 --> 00:10:51.759 even billions of simulated years. 217 00:10:51.960 --> 00:10:55.120 So they're essentially playing out a high speed, high precision 218 00:10:55.200 --> 00:10:58.600 video game of orbital mechanics, step by tiny step over 219 00:10:58.639 --> 00:10:59.679 cosmic time scales. 220 00:11:00.120 --> 00:11:00.879 Pretty good analogy. 221 00:11:00.960 --> 00:11:04.000 Yeah, And for this particular study by Patel and his team, 222 00:11:04.440 --> 00:11:07.600 they couldn't just model the simple point mass gravity. They 223 00:11:07.720 --> 00:11:10.759 had to include the really complex effects of tidal forces. 224 00:11:11.440 --> 00:11:14.519 The star raises tides on the planet and the moon 225 00:11:14.960 --> 00:11:17.799 the planet raises tides on the moon. These tides act 226 00:11:17.879 --> 00:11:21.480 like friction, They dissipate energy, they cause orbits to change. 227 00:11:21.559 --> 00:11:23.720 It all has to go into the simulation. 228 00:11:23.519 --> 00:11:26.399 And what were the key things they changed in these simulations? 229 00:11:26.440 --> 00:11:27.600 To see what mattered. 230 00:11:27.320 --> 00:11:30.840 Most, they varied two main factors. The mass of the 231 00:11:30.840 --> 00:11:34.440 host planet. They looked at planets around one Earth mass 232 00:11:34.639 --> 00:11:36.919 up to maybe two Earth masses, like a super Earth. 233 00:11:37.559 --> 00:11:40.919 And crucially, they varied the planet's orbital distance its semi 234 00:11:40.919 --> 00:11:43.399 major access within the habitable zone. 235 00:11:43.600 --> 00:11:45.919 That distance seems like it would be critical because the 236 00:11:45.960 --> 00:11:48.559 further the planet is from the star, the less the 237 00:11:48.600 --> 00:11:52.279 star interferes. Right. That defines the plant's gravitational. 238 00:11:51.720 --> 00:11:54.879 Turf precisely, and that turf has a technical name that's 239 00:11:54.879 --> 00:11:57.559 central to this whole problem, the Hillsphere. 240 00:11:57.639 --> 00:11:59.559 Okay, the Hillsphere explain that what is it. 241 00:11:59.639 --> 00:12:03.080 Visually imagine the planet is surrounded by an invisible bubble. 242 00:12:03.399 --> 00:12:06.919 Inside that bubble, the planet's own gravity is the dominant force. 243 00:12:07.399 --> 00:12:09.799 It's strong enough to hold on to an orbiting moon 244 00:12:09.879 --> 00:12:13.120 even with the star pulling from farther away. That bubble 245 00:12:13.240 --> 00:12:16.240 is the hill sphere. If the Moon orbits nice and 246 00:12:16.279 --> 00:12:19.600 deep inside the hill sphere, it's relatively safe. But if 247 00:12:19.639 --> 00:12:21.600 its orbit takes it too close to the edge of 248 00:12:21.639 --> 00:12:24.720 that bubble, or if the bubble itself shrinks, the spar's 249 00:12:24.759 --> 00:12:27.519 gravity can become dominant and it can pull the Moon away. 250 00:12:28.200 --> 00:12:30.600 Okay, so how does the hillsphere behave in these tight 251 00:12:30.759 --> 00:12:34.080 Endorf systems compared to say, our Solar system. 252 00:12:34.240 --> 00:12:36.360 Well, here, Earth is quite far from the Sun, so 253 00:12:36.440 --> 00:12:38.759 our hillsphere is pretty large, about one point five million 254 00:12:38.799 --> 00:12:41.759 kilometers across, plenty of room for the Moon, which orbits 255 00:12:41.759 --> 00:12:45.120 well inside that, but around an em dwarf the habitable zone. 256 00:12:45.159 --> 00:12:46.559 Planet is so close to the. 257 00:12:46.519 --> 00:12:51.240 Star that powerful stellar gravity constantly squeezes the planet's hill sphere, 258 00:12:51.279 --> 00:12:54.279 shrinking its zone of influence. The closer the planet orbits 259 00:12:54.279 --> 00:12:57.200 the star, the smaller its hill sphere becomes, and the 260 00:12:57.200 --> 00:12:59.399 smaller the hill sphere, the easier it is for any 261 00:12:59.440 --> 00:13:02.519 slight nutt or orbital evolution to push the Moon outside 262 00:13:02.559 --> 00:13:04.639 that boundary where the star can just snatch it. 263 00:13:04.919 --> 00:13:08.360 So the setup itself is precarious. The planet might be 264 00:13:08.399 --> 00:13:11.080 at the right temperature for liquid water, but it's in 265 00:13:11.159 --> 00:13:16.039 absolutely the worst gravitational neighborhood for keeping a large moon safe. 266 00:13:16.120 --> 00:13:18.399 The deck is stacked against the Moon from the start. 267 00:13:18.559 --> 00:13:19.919 That's the fundamental challenge. 268 00:13:19.960 --> 00:13:24.039 The simulations were designed to quantify, and the results, well, 269 00:13:24.120 --> 00:13:26.639 they paint a pretty bleak picture for the idea of 270 00:13:26.879 --> 00:13:30.919 Earth like worlds, with Luna like moons being common around. 271 00:13:30.639 --> 00:13:33.240 Most red dwarfs. The headline finding. 272 00:13:33.279 --> 00:13:36.240 The general rule that emerged is that rocky planets like 273 00:13:36.279 --> 00:13:39.320 Earth orbiting and the habitable zones of M dwarf stars 274 00:13:39.519 --> 00:13:42.600 are highly likely to lose any large lunicized moons they 275 00:13:42.679 --> 00:13:45.639 might form, and they lose them fast, typically within the 276 00:13:45.639 --> 00:13:47.480 first billion years of the system's life. 277 00:13:47.559 --> 00:13:49.200 A billion year sounds like a long time, but in 278 00:13:49.240 --> 00:13:51.399 planetary evolution terms maybe not. 279 00:13:51.399 --> 00:13:53.679 Compared to the four point five billion years Earth has 280 00:13:53.720 --> 00:13:55.960 had its moon. No, a billion years is short, but 281 00:13:56.000 --> 00:13:58.159 it gets much much worse when you drill down into 282 00:13:58.159 --> 00:13:59.840 the specific types of endwarf. 283 00:14:00.120 --> 00:14:02.720 Right, we can't just say M dwarfs. They range from hotter, 284 00:14:02.799 --> 00:14:07.039 brighter ones to much cooler, dimmer ones, and that classification 285 00:14:07.600 --> 00:14:10.559 M zero down to M nine must be critical here 286 00:14:10.639 --> 00:14:13.279 because it dictates how close that habitable zone. 287 00:14:13.159 --> 00:14:16.639 Is absolutely critical. The classification basically tells you the star's 288 00:14:16.679 --> 00:14:20.000 temperature and brightness. M zero stars are the hottest and 289 00:14:20.080 --> 00:14:23.240 brightest M dwarfs. Relatively speaking, M nine's are at the 290 00:14:23.320 --> 00:14:27.000 other end, tiny, ultra cool incredibly dim. Since the habitable 291 00:14:27.120 --> 00:14:30.279 zone location depends entirely on the star's heat output. This 292 00:14:30.320 --> 00:14:33.440 classification directly tells you how close an eight Z planet 293 00:14:33.519 --> 00:14:36.519 has to orbit, and M nine's habitable zone is practically 294 00:14:36.519 --> 00:14:38.919 skimming the star's surface compared to an M zero. 295 00:14:38.879 --> 00:14:43.320 And closer means stronger stellar tides, more hillsphere, squeezing more 296 00:14:43.399 --> 00:14:44.240 danger for the moon. 297 00:14:44.519 --> 00:14:48.639 Precisely so, the researchers ran detailed simulations, focusing initially on 298 00:14:48.720 --> 00:14:51.320 systems around M four dwarfs. These are kind of typical 299 00:14:51.480 --> 00:14:54.120 middle of the road red dwarfs. They simulated these star 300 00:14:54.200 --> 00:14:57.000 planet moon setups for two hundred million years to see 301 00:14:57.000 --> 00:14:57.759 what happened. 302 00:14:57.480 --> 00:15:00.360 Ok M four systems was the verdict? How long did 303 00:15:00.360 --> 00:15:02.879 those Luna like moons typically last? This feels like the 304 00:15:02.879 --> 00:15:03.600 moment of truth. 305 00:15:03.759 --> 00:15:06.960 The results were frankly shocking. For these typical M four 306 00:15:07.039 --> 00:15:10.000 dwarf systems. The simulation showed the average lifetime for a 307 00:15:10.120 --> 00:15:13.240 large Luna like moon was less than ten million years. 308 00:15:13.399 --> 00:15:16.480 Wait, ten million, not billion million, ten. 309 00:15:16.480 --> 00:15:22.120 Million years, ten mere. It's an incredibly short timescale. Cosmically speaking, 310 00:15:22.159 --> 00:15:25.399 it's basically instantaneous. The moon forms maybe and then puff. 311 00:15:25.200 --> 00:15:28.279 It's gone, Okay, wow, I need to process that ten 312 00:15:28.279 --> 00:15:31.559 million years. Let's put that against Earth's history again, Life's history. 313 00:15:31.720 --> 00:15:33.080 What does ten million years get you? 314 00:15:33.440 --> 00:15:37.039 Almost nothing in terms of complex evolution. Earth is four 315 00:15:37.039 --> 00:15:40.240 point five billion years old. It took hundreds of millions 316 00:15:40.279 --> 00:15:42.240 of years just for the planet to cool down, for 317 00:15:42.279 --> 00:15:46.320 oceans to form, for the atmosphere to stabilize somewhat. Simple, 318 00:15:46.440 --> 00:15:49.320 single celled life appeared relatively early, maybe within the first 319 00:15:49.320 --> 00:15:54.240 billion years. But complex life, multicellular organisms, animals, that'sok, billions 320 00:15:54.240 --> 00:15:56.919 of years. The entire Cambrian Explosion, the big diversification of 321 00:15:56.960 --> 00:15:59.919 animal life, happened around five hundred and forty million years ago. 322 00:16:00.200 --> 00:16:03.000 Dinosaurs existed for one hundred and sixty five million years. 323 00:16:03.039 --> 00:16:03.840 Ten million years. 324 00:16:03.840 --> 00:16:04.639 It's just a blip. 325 00:16:04.799 --> 00:16:07.919 So any benefits that moon might provide, the stable tilt 326 00:16:08.240 --> 00:16:11.600 the ocean tides stirring things up, they'd vanish before life 327 00:16:11.600 --> 00:16:13.600 had any real chance to take advantage of them for 328 00:16:13.639 --> 00:16:16.679 the long haul. The stability needed for billions of years 329 00:16:16.840 --> 00:16:18.039 is only there for millions. 330 00:16:18.480 --> 00:16:22.600 That's the devastating implication. The researchers explicitly state that ten 331 00:16:22.679 --> 00:16:27.240 million years is very short compared to the astrobiological, geological, 332 00:16:27.360 --> 00:16:31.120 or astrophysical time scales. It means the mood is effectively 333 00:16:31.279 --> 00:16:35.120 useless for fostering the kind of long term stable conditions 334 00:16:35.200 --> 00:16:36.799 complex life seems to require. 335 00:16:36.879 --> 00:16:38.759 And if that's the case for M four stars, what 336 00:16:38.840 --> 00:16:42.080 about the even cooler, dimmer ones, the M fives, M six's, 337 00:16:42.120 --> 00:16:44.559 all the way to M nine's, where the habitable zone 338 00:16:44.600 --> 00:16:45.720 is even closer. 339 00:16:45.559 --> 00:16:49.240 The prognosis gets even worse. Patel and the team extrapolate 340 00:16:49.279 --> 00:16:52.720 from their findings, they expect that habitable zone planets around 341 00:16:52.720 --> 00:16:55.559 those later type M dwarfs M five through M nine 342 00:16:55.799 --> 00:16:59.000 will lose their large moons even faster than ten million years. 343 00:16:59.519 --> 00:17:02.120 The stellar tides are just too overwhelming that close in. 344 00:17:02.240 --> 00:17:04.119 They rip the moon away almost immediately. 345 00:17:04.359 --> 00:17:06.799 So for the vast majority of red dwarfs, the most 346 00:17:06.799 --> 00:17:09.720 common stars. If planet forms with a big moon and 347 00:17:09.759 --> 00:17:14.359 the habitable zone, that moon is doomed, its lifespan is 348 00:17:14.440 --> 00:17:18.599 negligible on cosmic time scales. The system is actively hostile 349 00:17:18.599 --> 00:17:18.839 to it. 350 00:17:19.039 --> 00:17:21.440 That really seems to be the takeaway for mphorism later, 351 00:17:21.599 --> 00:17:24.000 and it's important to connect this finding the tidal tearing 352 00:17:24.119 --> 00:17:27.960 with other research that looked at a different problem, tidal heating. 353 00:17:28.359 --> 00:17:32.440 Ah right, So even if the moon somehow survived being 354 00:17:32.519 --> 00:17:35.079 ripped away, it might cook itself from the inside. 355 00:17:34.720 --> 00:17:35.960 Out potentially yes. 356 00:17:36.279 --> 00:17:38.920 Other studies suggested that even if a large moon managed 357 00:17:38.960 --> 00:17:42.000 to hang on for a while in that intense gravitational environment, 358 00:17:42.279 --> 00:17:45.000 the constant flexing and stretching from both the stars and 359 00:17:45.039 --> 00:17:48.200 the planet's gravity could generate enormous amounts of internal heat 360 00:17:48.240 --> 00:17:51.440 through friction. If it's an icy moon, maybe that creates 361 00:17:51.440 --> 00:17:54.960 a subsurface ocean, which sounds good like Europa, But the 362 00:17:54.960 --> 00:17:57.079 heating could be so extreme it makes the ocean too 363 00:17:57.119 --> 00:18:01.759 hot or drives runaway volcanism, rendering moon itself uninhabitable. 364 00:18:02.240 --> 00:18:04.400 So it's the double whammy for big moons around most 365 00:18:04.440 --> 00:18:07.440 e M dwarfs, they either get tidally torn away very quickly, 366 00:18:07.559 --> 00:18:10.400 or they get tidally heated into oblivion, a real lose 367 00:18:10.400 --> 00:18:11.160 lose situation. 368 00:18:11.519 --> 00:18:15.160 That phrase general fragility of exa moons in M dwarf 369 00:18:15.240 --> 00:18:18.680 systems really captures it well. For M four through M nine, 370 00:18:18.759 --> 00:18:21.359 the outlook seems incredibly poor. If you need a large 371 00:18:21.400 --> 00:18:23.839 stabilizing moon for planetary habitability. 372 00:18:24.160 --> 00:18:26.680 It's hard not to feel a bit deflated by that. Yeah, 373 00:18:26.720 --> 00:18:30.359 billions upon billions of star systems potentially hostile to the 374 00:18:30.400 --> 00:18:33.680 one feature that made Earth so stable, But science always 375 00:18:33.720 --> 00:18:37.640 has nuances, right? Were there any scenarios in the simulations 376 00:18:37.640 --> 00:18:41.359 where moons lasted longer? Any exceptions to this grim rule? 377 00:18:41.559 --> 00:18:44.680 Yes, thankfully there were. The simulations didn't just paint a 378 00:18:44.720 --> 00:18:49.079 picture of destruction. They also pinpointed the specific, somewhat rare 379 00:18:49.119 --> 00:18:53.359 configurations where large moons could survive for significantly longer periods. 380 00:18:53.759 --> 00:18:56.000 And the key factor, again was the star type. 381 00:18:56.039 --> 00:18:58.519 Okay, so where did they find more hope? Which M 382 00:18:58.599 --> 00:18:59.920 dwarfs offer a better chance? 383 00:19:00.240 --> 00:19:03.160 The hope lies almost entirely with the earliest, hottest and 384 00:19:03.160 --> 00:19:05.680 brightest en dwarfs, the M zero stars. 385 00:19:05.519 --> 00:19:08.240 M Zero's what makes them different enough to potentially save 386 00:19:08.279 --> 00:19:08.599 a moon? 387 00:19:08.880 --> 00:19:12.240 It all comes down to distance again. Being the brightest 388 00:19:12.279 --> 00:19:15.319 type of M dwarf, an M zero star's habitable zone 389 00:19:15.319 --> 00:19:18.279 is pushed significantly further out compared to an M four 390 00:19:18.400 --> 00:19:21.599 or an M nine. It's still closer than Earth's orbit, 391 00:19:21.960 --> 00:19:24.640 but it's far enough to provide a crucial buffer. That 392 00:19:24.799 --> 00:19:28.400 extra distance dramatically weakens the star's tidal pull on the Moon. 393 00:19:28.839 --> 00:19:31.559 It gives the planet its own gravity its hill sphere 394 00:19:31.680 --> 00:19:33.279 a much better chance to hold on. 395 00:19:33.680 --> 00:19:37.400 Okay, so moving the habitable zone outwards is key how 396 00:19:37.440 --> 00:19:39.480 much longer could a moon last around an M zero 397 00:19:39.559 --> 00:19:40.440 in the simulations? 398 00:19:40.680 --> 00:19:44.279 Significantly longer. The simulation showed that for a standard Earth 399 00:19:44.359 --> 00:19:46.720 mass planet orbiting in the habitable zone of an M 400 00:19:46.839 --> 00:19:50.119 zero dwarf, a large lunar like moon could survive for 401 00:19:50.240 --> 00:19:54.240