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If the sun's gravity is strong enough to pull a comet from the kuiper belt why does it not pull the planets into it?

I was told that the sun's gravitational pull is so strong that it pulls comets in from the kuiper belt, but why does it not do the same to the planets? Since a comet is so small in size ,mass and density and so far out how is this possible? An old teacher of mine said it has to do with the planets speed and its own gravity, but doesn't a comet move at a faster speed than the planets? Does the fact that comets do not have a gravitational field play into this? Or am I being mislead? This may be a basic question but I have not found an answer that explains this. This question and a few others is making me think I need to take astrophysics in college . Thank you.

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  • Nov 15 2012: "If the sun's gravity is strong enough to pull a comet from the kuiper belt why does it not pull the planets into it?"

    If you could stop a planets movement around the Sun (its orbit) it would fall in. Whether an object falling towards the Sun ends up in an orbit or crashing into the Sun depends on how that object approached the Sun in the first place: if it moved slowly, or just on a straight collision course with the Sun it will crash into the Sun, if it approached in such a way that it will "overshoot" the Sun, the Sun will still try to pull the object in and the object will enter an elliptical or circular orbit around the Sun that's stable because the centrifugal force of the orbit negates the gravitational force. In essence the object will be in eternal freefall (this is why astronauts are weightless when in orbit around the Earth).

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