Dido

Dido, also known as the Thirteenth Planet, (PROSE: The Rescue) was the homeworld of the Didoans and the sand beasts.

Astronomical data
Dido had at least three moons and a thirteen-hour day. It orbited two stars which, in turn, orbited one another, resulting in the planet travelling in an eccentric "figure of eight". As a result of this, the vegetation burnt up and the seas evaporated when it reached a critical position between the two stars, forcing the Didoi to retreat underground for hundreds of years. (PROSE: The Rescue) It was believed that there were no oceans on the planet. (PROSE: The Empire of Glass)

Dido was a light-year from Geldof Eight. (PROSE: The Rescue)

History
The First Doctor visited Dido prior to his travels with Ian Chesterton and Barbara Wright. Due to the Didoi's cycle of hiding underground for centuries during the critical period, (PROSE: The Rescue) they numbered only about a hundred when the Doctor met them. (TV: The Rescue)

In or soon after 2493, the UK-201 crash-landed on the planet. The only survivors of the wreck were Vicki Pallister and Bennett, the latter a murderer who killed the other survivors and the natives of Dido, apart from two who survived. The First Doctor and his companions arrived on Dido in the TARDIS. They discovered the truth behind Bennett, and Bennett fell off a cliff while trying to run from the surviving Dido natives. The travellers took Vicki away in the TARDIS with them. (TV: The Rescue)

The planet was protected under the Galactic Heritage. (PROSE: The Tomorrow Windows)

The Seventh Doctor and Melanie Bush once visited Dido. (AUDIO: Maker of Demons)