Star Fissure is an anomaly of the age of Riven that appears as a rift between two separate systems. Beneath it is a star field. It eventually leads to the home of The Stranger, presumably Earth. Its origin is unknown, as nobody wrote it into the age purposefully. Gehn theorized that the fabric of Riven has been breached in a way that permits matter to be hospitably exchanged between two discreet but overlapping spaces - much like a Link.Gehn considered that it was actually an unexpected by-product of the changes Catherine and Atrus wrote into the Age during their escape, and it was not written on purpose, as they wouldn't want the world (and him) destroyed. Catherine's visions tell that it was born out of the will of the Maker to serve some greater purpose.