Something I've thought about before but never asked anybody...The existence of short-period comets is a problem if one believes the solar system is 4 billion years old, because obviously after that length of time all of the short-period comets would have disintegrated. So, we need a way of replenishing them, hence the Oort cloud. So there's a dormant, potential comet floating out there in the Oort cloud. But what I am wondering is this... If the object from the Oort cloud simply drifts into the solar system it seems that it will simply be pulled into the sun. In order to become a short-period comet orbiting the sun, it needs some kind of force directing it a point a distance away from the sun, so that when it approaches that point the sun's gravity will sling-shot the object and force it into an elliptical orbit around the sun. Is my understanding of physics correct, that it needs something to force it towards a point a distance away from the sun? But how does the object get that force, where does it come from?