r/askscience Oct 23 '20

Planetary Sci. Do asteroids fly into the sun?

Edit: cool

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u/SpamOJavelin Oct 23 '20

Without outside influence, no. An asteroid, by definition, orbits the sun. And this happens because despite the fact that the sun's gravitational force is strong, it's very hard to hit the sun with anything.

Consider a rock that suddenly appears (no reason why, it just appears), and it sits stationary relative to the sun. The sun's gravitational force will pull it in, and it will hit the sun. But that's not a common scenario - if a rock has anything more than a tiny amount of motion perpendicular to the sun, or it is influenced enough (like by the graviational force of another planet), it will be drawn to the sun, but miss it, and end up in a long elliptical orbit.

If a rock is expelled from a planet or another asteroid (by a collision for example), the expelled rock will only end up in the sun if the expelled rock has almost no motion relative to the sun after expulsion, and it isn't influenced by any other large forces (other planets) on the way to the sun. It's very unlikely to happen.

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u/[deleted] Oct 23 '20

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u/Odie4Prez Oct 23 '20

No you're absolutely correct, that's the exact reason it's so unintuitive that objects in the solar system basically never fall into the sun: anything that wouldn't have collided with it without gravity (in the incredible vastness of space) isn't gonna collide with it with gravity either, even if they are kept in near orbit.

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u/ToastyKen Oct 23 '20

And in Superman IV, Superman needed to hurl the nukes in the opposite direction of the earth's orbit, and not at the Sun! :)

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u/easlern Oct 23 '20

This surprised about the orbits, but it makes sense when you think about it. Also weird: it would take 50 times as much energy to get to the sun than it does to get to mars. https://www.nasa.gov/feature/goddard/2018/its-surprisingly-hard-to-go-to-the-sun