Eternal Planetary Systems: Building for Perpetuity.
A study published in MNRAS explores how a super-advanced civilization might pack a bunch of planets into the habitable zone of a single star. The team found that as many as 24 Earth-like worlds could be packed into stable horseshoe resonances, sharing a common habitable zone. Such a system could prove the existence of an advanced civilization if the orbits were aligned to pass in front of their star from our vantage point, and we could detect them as exoplanets using the transit method.