Etarho was a gas giant. Its name was derived of letters in the old Greek alphabet: "eta" and "rho". The Valeyard claimed that, in his final incarnation, the Doctor spent some time on a satellite orbiting Etarho, trying to break the twelve-regeneration limit imposed by Rassilon on the Time Lords. The Valeyard also claimed to have been born on the satellite as a result of the Doctor's experiments, and having spend the first twenty years of his life there before being rescued by prospectors.
Inquisitor Darkel brought Space Station Zenobia into orbit around the planet when putting the Valeyard on trial. The satellite was translocated to another timeline by the Time Lords during the trial in order to hide the evidence the Valeyard claimed was there. (AUDIO: Trial of the Valeyard)