Humans place too much importance in what they call velocity vectors, which are only a mathematical representation. The motion of asteroids or comets or planets is there for a reason. It is not, as humans frequently assume, because the motion was set in place for some reason long ago and things just follow. The motion does not rule! The motion is a result, not a primary force. Humans treat motion as though it stood alone, outside of all other factors. What caused the motion? All motion is a result, from the acorn dropping from a tree, or the wind swaying branches as air masses move to equalize, to the motion of the planets in their orbits.
The breeze that bows a young sapling over a bit will not keep that sapling bent when the breeze stops blowing. Just so, an object may even be stopped in its course, but only for a moment. Then on it comes, impelled by the same factors that impelled it in the first place, as its motion was determined by the gravity pull of objects nearby, and those objects have not moved! An object will be motionless in space for one of two reasons. An object in the absence of gravity from outside influences has no reason to move at all, and is still only because there is no call to do otherwise. It does not have inertia, or a reluctance to move. Objects have inertia when they are caught in the grip of a gravity influence, and most often in the grip of several gravity influences. Therefore, when undertaking the study of motion, limiting the examination to the object and its speed is only effective when all other factors hold steady.