With probability close to 100% there are no aliens in the Solar System. At present we only can meet alien, if they'll land here. They don't for some reason. Very simple: if they are at the level, comparable to ours, they cannot travel so far. If they can travel at star distances, they are not interested to land here - there are so many interesting things somewhere else. If we are assume that some unusual phenomena in the space, looking unnatural, are signs of activity of advanced civilization, then there are plenty... Check my today's post, for example