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Tim

Asteroids and their relative velocities

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I've been following somebody on Facebook who regularly images asteroids, and indeed has identified a few of his own.

But this got me to wondering, do these orbiting bodies, of which there must be many thousands, all reach the same kind of velocity?

I guess there are various factors involved. This new asteroid from another galaxy is also intriguing.

For what it is worth, here are a couple that I have observed in the past:

 

 

 

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Most of the asteroids we are aware of will be in an elliptical orbit around our sun, more or less, and their velocity basically depends on the size of their orbit and how far round they are in that orbit. See Kepler's third law. Like comets, and anything else, it will get faster as it swings round the sun, and moves more slowly when it's out at the furthest point in it's orbit. But their orbits may be perturbed by other objects, like Jupiter or us, etc.

If something can speed up so that it's travelling fast enough to exceed the escape velocity of the object it is orbiting, like firing a rocket leaving Earth and firing its booster for long enough, then it's not coming back - it will orbit something else, like the sun, or the galactic center, etc. On the other hand, if an object coming into our solar system already exceeds escape velocity as it passes the sun and doesn't slow down while it's passing through, then it's not going to get captured by our sun's gravity though might get deflected... like the recent asteroid, presumably from another star rather than another galaxy. All the rest of the asteroids are slower than that, they're orbiting the sun, perhaps not very stable orbits because of the pull of Jupiter and other planets, but unless they bump into something or take a dive round a planet, they're not really going to speed up. And their velocity should depend only on the shape and size of it's orbit. The one that came from elsewhere was travelling super quick! It would have to have been to leave it's old star, and certainly fast enough not to settle round ours.

When an asteroid or comet gets redirected to some degree by Earth or moon on it's way round the sun, I think the maths of a graze like that deals with a hyperbolic trajectory with respect to the body it's passing, but I think the basic understanding of how it all works is underpinned by velocity and elliptical orbit round the primary body ie sun. Space travel is about delta-v, ie change in velocity needed to leave A and reach B, then change in velocity needed to not shoot pass B but to be captured by B, etc.

That's my understanding of it all. I've not tried imaging any, but do remember hunting one down in the 15x70s a few years ago that passed close.

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