A very good question, and I don't think anyone has looked into this. My guess is that a 10 kilometer body hitting a 12,000 kilometer planet isn't going to do much. The orbital velocity of the Earth is about the same as the impact velocity of the asteroid, so the kinetic energy of the impact depends mostly on the masses of the bodies. The mass of the Earth is 10^27 grams, a 10 kilometer asteroid is worth about 10^19 grams, so the energy of the Earth in its orbit will only be affected by the ratio of their masses or 1 part in 10 million. This is not going to be enough to change the Earth's orbit by more than a few kilometers at the outside.