Also, since we're being pedants, we can't actually be certain that the sun is the only star in the solar system. While there is no evidence of such things existing, there's also no way we can be certain that relic black holes do not exist... that is, black holes that are almost fully evaporated, but cannot evaporate further. This could be dark matter. Given our best understanding of black holes is that they are the end state of massive stars, I can argue that there could be a ludicrous number of "stars" in the solar system for all we know.