From Destinypedia, the Destiny wiki
A year after the conclusion of the Red War, the Guardian was summoned to Io by visions, and witnessed the Cradle emitting enormous pulses of Light. It is considered likely that the Cradle, and Io itself, remain connected to the Traveler through its remnant energies.
When the Pyramids returned to the Sol System, one massive Pyramid and a fleet of attendant vessels settled over the Cradle. The Guardian was dispatched to investigate the Cradle and search for Eris Morn, who had ventured inside. In the hollow at the center of the Cradle, Eris and the Guardian discovered a "tree of silver wings" with a seed beneath its roots.