I think a ship might fit the space nicely (although it looks pretty without)... However, if you throw the ship in, a big deal for me would be "how do I give a sense of scale?" The ship will need to be relatively small so it doesn't crowd the space, BUT you don't want to give a false sense of scale. Is the ship as big as the planet? Is there a way to cheat the scale without anyone noticing? etc. etc. You don't want anyone thinking its about a little mini space ship that will fly into that person's nose. That said, I do think a station orbiting the planet, or some type of space craft would make the image better if implemented well. As is, looks fine. =)