Speaking of totally awesome stuff that advanced aliens might be doing, in the future we might be able to detect the ways they produce power, like mining stars and fuelling ships with antimatter. A little bit of background first: There's this thing called the Kardashev scale which is used to measure and predict how advanced an intelligent race is, mostly by looking at how they get their energy. As humans are still burning fossil fuels, we don't even make it to level one yet. A level two civilisation, however, might use techniques such as "star lifting", which involves removing chunks of matter from neighbouring stars to use as fuel. Even more badass, they might just cut out the middle man and feed a star into a black hole and harvest the photons from the accretion disc. Even a level one civilisation should have mastered the use of antimatter as a super efficient fuel (incidentally, star lifting might well generate a lot of antimatter for this). A way we could detect this is to detect the "exhaust fumes" made up of gamma ray emissions. An alien race might be using this technique to power their spacecraft. Level three and above on the Kardashev scale would probably also have a pretty huge presence in the solar system, however, they might actually be too advanced at that point for us to even know what to look for.
