Eli5 Who do all the planet not eventually get sucked into the sun?
In: Physics
To get sucked in, they would have to lose their momentum and energy. But what’s going to do that in space? Nothing really.
A well lubricated, low friction clock pendulum can swing for a very long time, a massive planet flying through basically empty space experiences essentially zero friction. They can keep flying in a circle around the sun because they have the speed to do that and aren’t losing it.
But how did they all end up with enough energy to keep flying around the sun? Wouldn’t some of them have less speed and a path that would eventually hit the sun? Absolutely, and that happened a few billion years ago. The current planets, moons, asteroids, and meteors in their present configurations are not all that ever existed in our solar system. Lots of things fell into each other when the solar system was young.
Will they ever fall into the sun? It there a very small amount of friction slowing them?
Yes. The inner planets will end up in the sun. Definitely mercury and venus. Probably earth. Probably not mars. Not because they fall it, but because the sun will grow to a red giant before it dies and engulf them.
But ignoring the sun ever dying, foreseeably the planets would eventually decay. There is gravitational waves, and gravitational orbits do trigger tiny amounts of these waves that carry away energy and momentum. In a few trillion or more years, longer than the existence of the entire universe so far, the planets might fall into the sun. Sun of course by then will be a small, cold black ball rather than a star. Life as we know it will be long dead and impossible to exist.
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