 The volume of space within which an object can be said to orbit Jupiter is defined by Jupiter 's Hill sphere ( also called the Roche sphere ) . When the comet passed Jupiter in the late 1960s or early 1970s , it happened to be near its aphelion , and found itself slightly within Jupiter 's Hill sphere . Jupiter 's gravity nudged the comet towards it . Because the comet 's motion with respect to Jupiter was very small , it fell almost straight toward Jupiter , which is why it ended up on a Jupiter @-@ centric orbit of very high eccentricity – that is to say , the ellipse was nearly flattened out . 
