So far we have only heard the Bungie confirm playable ares in our own solar system but they could still announce new planets like they did at E3 with Jupiter and Mercury. Also, these hostile aliens definitely didn't come from our solar system so I could see guardians going to our enemies home planets to crush them like they attempted on us, after we win our own solar system back of course. We have seen some pretty advanced vehicles in game-play and in trailers so I think humans will most likely have the technology for exploring out of our solar system. This would probably take place at the end of the Destiny story or in sequels to Destiny.