WEBVTT 00:00.000 --> 00:12.640 Let's talk about the rarity of our Earth and how special it is. 00:12.640 --> 00:16.920 How about how it is protected from the dangers of the space, unlike other celestial objects 00:16.920 --> 00:19.880 – the meteors, asteroids, and others. 00:19.880 --> 00:25.680 Although space is full of them, and our Earth can get hit, this happens very rarely, especially 00:25.680 --> 00:28.180 on levels that could be dangerous. 00:28.180 --> 00:30.300 We only hear news of close calls. 00:30.300 --> 00:33.520 Can you tell us about the way our planet is protected? 00:33.520 --> 00:38.780 The atmosphere, the Van Allen Belt, does our solar system have a protection too? 00:38.780 --> 00:42.620 Are we located in a protected part of the galaxy? 00:42.620 --> 00:50.720 A very interesting topic is the situation, the placement of the Earth in the context 00:50.720 --> 00:52.000 that it is. 00:52.000 --> 00:57.700 So the Earth is part of our solar system, the solar system is part of our galaxy, and we 00:57.700 --> 01:02.640 can ask the question, is the Earth occupying a special place? 01:02.640 --> 01:05.320 Is it well protected, for example? 01:05.320 --> 01:11.820 The first thing to point out is that in our galaxy, at the galactic scale, there are very 01:11.820 --> 01:16.460 strong physical effects, for example supernovae, that are occurring. 01:16.460 --> 01:24.780 When a supernova occurs, a massive star explodes, and its energy output briefly matches the energy 01:24.780 --> 01:26.720 output of the entire galaxy. 01:26.720 --> 01:31.680 Now the entire galaxy is 100 billion stars, so it's 100 billion times its normal energy 01:31.680 --> 01:32.900 output. 01:32.900 --> 01:37.660 As such, when that occurs, for many, many light years around it, any possibility of life would 01:37.660 --> 01:38.980 be sterilized. 01:38.980 --> 01:40.900 There would be no possibility of life. 01:40.900 --> 01:47.500 So, and even much farther distances, as these supernovae are going off, there is these galactic 01:47.500 --> 01:54.720 cosmic rays that are a source of potential harm to the Earth. 01:54.720 --> 02:03.580 But our solar system has essentially a magnetic field that is protecting it. 02:03.580 --> 02:09.820 And in particular, there is a solar wind, which is this radiation from the sun, that modulates 02:09.820 --> 02:14.180 or moderates the effect of these galactic cosmic rays. 02:14.180 --> 02:18.120 The solar wind, in that sense, is helpful. 02:18.120 --> 02:22.920 But in another sense, the same thing that the processes that give us the solar wind give 02:22.920 --> 02:28.980 us sometimes dangerous events, like coronal mass ejections, where the sun occasionally has 02:28.980 --> 02:33.420 a big output, then how do we get protected from that? 02:33.420 --> 02:38.140 It turns out, if you look at Venus, Venus is getting, was essentially destroyed as a 02:38.140 --> 02:44.620 habitable planet by the sterilization or stripping of the hydrogen from its atmosphere. 02:44.620 --> 02:47.480 And so all that is now there is carbon dioxide. 02:47.480 --> 02:52.860 At the temperature in the surface of Venus, it's much hotter than your ordinary oven. 02:52.860 --> 02:56.860 So that's why nobody sends spacecraft there, because your electronics will melt after a little 02:56.860 --> 02:58.380 while in Venus. 02:58.380 --> 02:59.760 It's very difficult. 02:59.760 --> 03:00.760 Earth is not like that. 03:00.760 --> 03:02.240 What's going on? 03:02.240 --> 03:04.500 Earth has a magnetosphere. 03:04.500 --> 03:10.180 There is a molten liquid iron core that's spinning inside the Earth. 03:10.180 --> 03:14.580 And the dynamo process essentially generates a magnetic field. 03:14.580 --> 03:22.140 And the magnetic field then modulates and moderates the effect of solar radiation, the solar particle 03:22.140 --> 03:24.580 radiation. 03:24.580 --> 03:29.780 So the Earth is, on the one hand, protected from galactic cosmic rays by the sun, and then 03:29.780 --> 03:37.240 it is protected from the sun by its own magnetosphere. 03:37.240 --> 03:42.780 And so there is this layer after layer of protection for the Earth, just from the standpoint 03:42.780 --> 03:44.640 of particle radiation. 03:44.640 --> 03:49.260 There's also very interesting things going on in this that I could go on, but I think this 03:49.260 --> 03:53.020 part expresses just the levels of protection that the Earth has.