[akomtu]

If I were to make a sci-fi plot, I'd say the first nuclear blast in a US desert (Mohave?) spooked the aliens because they happen to live somewhere around that desert, in a "different dimension" so to say. To them the blast was a spike of hard radiation of unexplained origin. After digging into it, they've realized the relationship with us (to their astonishment) and developed an entire new branch of science about cross-dimension space travel. Now they can regularly send equivalents of bathyscaphes to our plane and observe us. They don't space travel as we imagine it, they rather submerge. The bathyscaphes protect their bodies from instant disintegration, but they already have a prototype of a space-suit that will let them leave the bathyscaphe. In the meantime they've been dropping some artifacts to steer our civilization in the desired direction. They really want us to develop an advanced machine civilization because they have means of directly connecting to a certain type of machines. As for their goals, it's the same goals that we have for Mars or Moon: explore and colonize because we can, perhaps find some minerals.