- Let’s talk about the rarity of our earth and how special it is. How is it protected from the dangers of the space, like celestial objects, meteorites, asteroids and others? Although space is full of them and our earth can get hit, this happens very rarely especially on levels that could be dangerous. We only hear news of close calls. Can you tell us about the way our planet is protected? The atmosphere, the Van Allen belt? Does our solar system have a protection too? Are we located in a protected part of the galaxy? - A very interesting topic is the situation, the placement of the earth in the context that it is. The earth is part of our solar system, the solar system is part of our galaxy. And we can ask the question, "Is the earth occupying a special place? Is it well protected for example?" The first thing to point out is that in our galaxy, at the galactic scale, there are very strong physical effects. For example, supernovae that are occurring. When a supernova occurs, a massive star explodes and its energy output briefly matches the energy output of the entire galaxy. Now the entire galaxy is a hundred billion stars; so it is a hundred billion times its normal energy output. As such, when that occurs, with for many many light years around it, any possibility of life would be sterilized. There would be no possibility of life. So, at even much farther distances, as these supernovae are going off, there are these galactic cosmic rays that are a source of potential harm to the earth. But our solar system has essentially a magnetic field that is protecting it and in particular, there is a solar wind which is this radiation from the sun that modulates or moderates the effects of these galactic cosmic rays. The solar wind in that sense is helpful. But in another sense, the same thing, the processes that give us the solar wind, give us sometimes dangerous events like coronal mass injections where the sun occasionally has a big output. Then how do we get protected from that? It turns out, if you look at Venus, Venus was essentially destroyed as a habitable planet by the sterilization or stripping of the hydrogen from its atmosphere. So all that there is now is carbon dioxide and the temperature at the surface of Venus is much hotter than your ordinary oven. So that’s why nobody sends spacecraft there, because your electronics will melt after a little while in Venus; it's very difficult. Earth is not like that. What’s going on? Earth has a magnetosphere. There is a molten liquid iron core that ‘s spinning inside the earth and that dynamo process essentially generates a magnetic field. And the magnetic field then modulates and moderates the effect of solar radiation, the solar particle radiation. So the earth is on the one hand protected from galactic cosmic rays by the sun, and then it is protected from the sun by its own magnetosphere. So there is this layer after layer of protection for the earth, just from the same point of particle radiation. There is also very interesting things going on in this that I could go on but I think this part expresses the levels of protection that the earth has.
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