How can Jupiter's gravity eject asteroids from the solar system?

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ExNihilo
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Hi,

I read sometimes that the gravity of Jupiter is enough to eject an asteroid or comet out of their orbit and fling them outside of the solar system.

But gravity is an attractive force, how can it eject something? Thanks for any clarification.
 

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Because things move. EDIT: Meaning that they are moving before the gravitational encounter occurs. And sometimes what gravity does is just change the trajectory of an object. Sure, the acceleration is towards Jupiter, but the effect of that is to change the trajectory of the object into one that is unbound and heads out of the solar system. You can think of it this way -- not all of the object's initial velocity is towards Jupiter (i.e. in the radial direction). Some of it may be in the perpendicular (tangential direction). So the object speeds up as it approaches Jupiter, but because it is not heading directly towards it, it misses it, and kind of "slingshots" around it on a curved path.
 


The slingshot effects works because during the interaction when the satellite passes "behind" the path Jupiter is traveling, Jupiters speed is slightly decreased, and since momentum is preserved, the satellites speed is greatly increased. (Note that these velocities are relative to some frame of reference, such as the Sun).