If aliens are in this solar system I would think they would find Ceres interesting. It is large enough to have enough gravity to keep things like structures in place, but light enough to not have fully differentiated which means there are probably heavy useful elements on the surface like gold, uranium, rare earths, and if there are any super heavy natural elements, they would likely be present on the surface as well. In addition leaving Ceres requires very little energy to escape it’s gravity well so it would make a good place to operate from.
