i think if you want it more believable then perhaps add some motion blur, or add some noise to match the pixel compression of the footage. also its just a simple sphere right now, so maybe you could try using your spaceship challenge entry in its place or model another more detailed ship. I would also suggest you try to match the lighting
Think about how the camera moves, it is kind of a nodal pan i guess. if you were filming a UFO I'd imagine you would follow the flight path. you could have it coming from behind the camera and going into the distance.
PS: I don't believe you!