Also, be very careful in your assumption that the "Hydaelyn system" looks anything like a real-life star-with-orbiting-planets would. This is a fantasy universe, and there might not be anything like a "solar system" at all. Rather than being a tiny speck orbiting an enormous ball of nuclear fusion, it's entirely possible that the planet IS the center in this model, with a small sun orbiting around it to provide light, an object similar in size and motion to the moon, but much brighter and warmer. Certainly, individuals in the game are fond of referring to the planets themselves as "stars".

There may well be no other planets in the solar system, because there's no system for them to be in - or if they do exist, they could be even tinier objects rotating around Hydaelyn!