Polaris... or the Moon. That would be amusing.
Suspect not- Polaris is too tied in historically with the Thargoids, & Luna is too intimately tied to Earth. Raxxla was supposed to be a wandering planet & if Luna disappeared the effect on Earth would be catastrophic as it has a stabilising effect on Earth’s orbit; FD try to stick to scientific plausibility. Besides Luna was mapped pretty closely for the Apollo programme so any alien structures would have been found. Mars is a possibility perhaps; does it have Phobos & Deimos in-game? Seem to remember some comment IRL that one of those may have been captured (DBOBE is quite keen on real astronomy). Merope 5C seems like it was captured but that’s too tied in with Thargoids again, and we’d have spotted alien structures there by now.