Phaester Osiris

Phaester Osiris was the home planet of the Osirians. It was a hot and dusty planet. (PROSE: Legacy) It had one moon, Beta Osiris. (PROSE: Scarab of Death) Signs of the Osirian's civilisation could be found on the planet, such as the especially tall pyramids. (PROSE: The Dark Path)

Circa 5000 BC, Phaester Osiris was ruled by Horus and Sutekh. When Sutekh started his reign of destruction, Phaester Osiris was one of the targets. Only Horus and seven hundred forty other Osirians survived the destruction of their home-world. (TV: Pyramids of Mars)

In 3985, the Braxiatel Collection funded an expedition to investigate the planet. Professor Rhukk helped discover the Horun ruins. (PROSE: Legacy)

Behind the scenes
Though it was implied that Phaester Osiris was destroyed by Sutekh, it apparently still existed in the 40th century.