Wait til we discover the launchpads in the geologic record.
I have it on good authority that the dinosaurs didn't go extinct, they predicted the Chicxulub collision and escaped the Earth on arks. Of course they realized that their warm blooded servitor species would survive the impact and evolve sentience much like their own (they created our genomes, so it was easy to predict), so they hid the launchpads until we would be ready to see them.
The arks landed on Planet 9 (the big one, not the lil one), since it was less likely to be hit by similar events. They hollowed it out, helping to create Pluto and Ceres, and have been living in there ever since.
Discovering the launchpads will show them that we've achieved sufficient technological prowess for them to reveal themselves to us. I can't wait!