Since enemy races are native to certain planets and maybe moons, I guess it's a good way to introduce new enemy or maybe even guardian races. 8 planets is too much for there concept to start with. This way would work in the long run and Bungie will make better quality gameplay and content. Its not that we wont get enough content, it's the curiosity to explore the other planets and locations we hear about will kill us. The confirmed locations include: Earth, Mars, Venus, the Moon and Europa. Just those will be enough. However Mars has two moons, Phobos and Deimos that will probably be explorable and all the abandoned satellites and spaceships. Those alone could be huge locations. Europa is Jupiter's moon so maybe Jupiter is next in line.