Athame is a hydrogen-helium gas giant with spectacular rings. The planet's apparent magnitude varies when seen from Thessia based on atmospheric conditions and relative distance. To the ancient asari, the "mysterious star" that shone in some months and disappeared in others was linked to fortune, and so it was named Athame, after the matriarch of the pantheon and a goddess of prophecy and fate. Athame's worship changed over time, eventually becoming the basis for a monotheistic religion in which her maiden, matron, and matriarch aspects oversaw all stages and roles in asari society. When an asari says "by the goddess," they are referring to Athame.
Like Janiri, the planet Athame served as a rally point during the Reaper invasion, where fleeing asari ships could discharge their drive cores so they could make another FTL jump. The Reapers were forced to chase the asari away from the planet, buying Thessia valuable time.