I haven't looked at the code he gave you but there are two ways of doing what you ask. The hard and most flexible way is to implement gravity physics into your code where the asteriod scans the planets and such for their mass and based on its proximity moves based on the gravity that effects it. The easy way and less flexible way is to give the asteroid a uneven radius (x has one radius length, and y has a different one) this would give an oblong path of movement, and then you would place its origin wherever you deem appropriate, but all of this would be manual, but very easy going on your computer.