The correct answer is
comets
Comets, in fact, follow a very elliptical orbit around the Sun. In fact, they have the most elliptical orbit of all astronomical objects. According to Kepler's second law, the velocity of an object orbiting the Sun depends on its distance from the Sun: the closer it is to the Sun, the faster it moves, and the further it is, the slower it moves. Due to their very elliptical orbit, the distance of the comets from the Sun change a lot, therefore they experience the most drastic change in velocity (more specifically, they move very fast as they approach the Sun, while they move very slow when they are very far from the Sun).
