The Trill system is a binary star system in which Trillius Prime, the Trill homeworld, is located. Trill is part of the Kalandra sector in the Alpha Quadrant of the Milky Way Galaxy. (ST reference: Star Charts) Starbase 51 is the closest Starfleet base to the the Trill system. (DS9 - Mission Gamma novel: Lesser Evil) In 2265, Starfleet discovered a comet heading towards Trill just outside the Trill system. The Starfleet team noted that the comet did not match the cometary halo that surrounded the star system. (DS9 - The Lives of Dax short story: "Sins of the Mother")