The Earth has at times been struck by very large asteroids but this has not knocked our planet out of it's orbit. Why not? Does the Earth have some method of 'self correction'? Or is it not a very 'fine tuned' system so that a few impacts really wont make any difference? Alternatively have we already been knocked from our orbit but just slightly so we won't notice it for millions of years? What about the increase in mass that our planet experiences? Wouldn't the planet have to orbit faster to maintain circular motion to compensate for this? Thanks very much. Any thoughts would be appreciated.