Phaester Osiris, (PROSE: Doctor Who and the Pyramids of Mars) also called the Throneworld (AUDIO: The Ship of a Billion Years) and stylised as Phæster Osiris, (PROSE: The Sands of Time) was the home planet of the Osirians.
It was a hot and dusty planet (PROSE: Legacy) located in the constellation of Orion. (PROSE: The Sands of Time) It was orbited by one moon, Beta Osiris, (PROSE: Scarab of Death) and the energy production facility Amenthes. (COMIC: Old Girl) It was known for its extraordinarily tall pyramids. (PROSE: The Dark Path)
Circa 5000 BC, Phaester Osiris was ruled by Horus and Sutekh. (TV: Pyramids of Mars) According to one account, after the Osirian Court slipped its moorings and cut itself off from history, its homeworld was considered a liability, so Sutekh destroyed it. (AUDIO: The Judgment of Sutekh) The Fourth Doctor claimed in 1911 that this event, some seven thousand years earlier, had begun Sutekh's "trail of havoc across half the galaxy". (TV: Pyramids of Mars)
Other accounts claimed that Phaester Osiris existed into the 40th century. (PROSE: Scarab of Death, Legacy) In 3985, the Braxiatel Collection funded an expedition to investigate the planet. Professor Rhukk helped discover the Horun ruins. (PROSE: Legacy)