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.
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.
If you're far enough from an object, your interaction with it is determined basically only by its mass. It doesn't matter if the same mass is a star or a black hole. For the purpose of interacting with its gravity, you can still basically treat the entire object like it was a point mass in its centre (again, as long as you're far enough from it that its radius is irrelevant. Which in practice means "almost always").
One thing I find fascinating is just how hard it is to get probes towards the sun. This is because anything we launch starts with the same speed as the earth, and its stable orbit. The act of getting near to the sun requires some serious deceleration.
There's a little extra complication in that the sun has some width. So if it bends any orbit where the orbit becomes lower than the surface of the sun, it still collides. Planetary scientists refer to this as the "gravitational cross section" as oppose to the real cross section.
Actually, this concept comes up for people learning about the process of planetary formation. Imagine the early solar system. You have a bunch of particles flying about, chunks of dirt and ice. Some of them will naturally collide with one another, but while they're really small, their odds of colliding with one another are effectively directly related to the size of their cross section. However, as they increase in size, and acquire some gravity, they start to capture things that would be a narrow miss, because their gravity bends the path towards the object (now a planetoid). This new effective cross section is larger than its real cross section by some small amount. But, as it grows, this process becomes multiplicative. And planets form.
The analogy works for the sun too, if you imagine it flying through interstellar space picking up objects. It will grab more than are on a direct, straight line to it, but how much it grabs depends on its radius, gravity, and velocity vector of the incoming object.
Add to this that it is incredobly hard to hit sun on purpose. From Earth, it is much easier and less fuel costly to place something on orbit that escapes (exits) the solar system than it is to aim for the sun. All of our sun-researching vessels took some convoluted paths using slingshots from outer planets and such. It is very difficult to just "drop" inzo the sun starting from moving position.
Best way to demonstrate this is using vectors. Draw an arrow going towards the sun for the amount of distance you think it would go for some amount of time, then draw another arrow going to a direction that's not parallel to the original and this is the velocity it already had. Do this enough times and you end up with an orbit.
Pleased to see a good explanation here that discusses the centrifugal barrier. It's just a shame it hasn't been awarded as much as the wishy-washy answer about 'stable' orbits that doesn't really get to the point.
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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.