But what kind of evidence could we have? Sure, if we would find crashed space ship, that would be good evidence. We don't have that (or it's not public knowled

But what kind of evidence could we have? Sure, if we would find crashed space ship, that would be good evidence. We don't have that (or it's not public knowledge anyway). Anything less than that would be hard to consider evidence. Especially if those things are trying to minimize encounters. As to mining planets. I think that it makes more sense to mine asteroids. You don't need to overcome gravitational well and asteroids are quite rich when it comes to resources. Asteroid belt is huge. You can build lots of stuff there without fear to be noticed. Also it's not really clear how far can you go with minituatirization. We think about big ships but if you can operate on molecular level, may be you can stay small. Think about robots size of bacteria, size of ants and stuff like that. Alien anthill in some asteroid pit might be never noticed.