Esto

Esto was a planet located in Lagoon Nebula. (WC: Number 1, Gallows Gate Road) It was home to a species of psychic parasites (WC: Number 1, Gallows Gate Road) and a species of telepathic plants that screeched when anyone stood between them, thus disrupting their communication. The First Doctor and Susan had visited Esto. (TV: The Sensorites) At some point in its history, Esto was placed under the protection of the Galactic Heritage. (PROSE: The Tomorrow Windows)