databank
900 year diary
interference by the nemesis comet
When the Doctor left Gallifrey, he took with him a sentient metal, called Validium. During a stay in seventeenth century England, the Validium was discovered by Lady Peinforte, who had it modelled into a statue of herself. Realising that the Validium could impart information Lady Peinforte was not ready for, the Doctor launched the statue into space where it became known as a comet. It passed close enough to Earth every twenty-five years to allow its influence to cause periods of unrest or disturbance such as World War Two, the assassination of Kennedy and other such disasters.