C.S. Lewis calls Earth Thulcandra in Out of the Silent Planet. The name means the “silent planet” in the book’s invented interplanetary vocabulary, because Earth is isolated from the wider community of inhabited worlds.
The novel’s protagonist, Elwin Ransom, learns this designation after being taken from Earth to Malacandra. On Malacandra, he encounters intelligent beings who understand Earth’s history through the idea of a planetary fall and separation.
Malacandra is the local name for Mars, while Perelandra is the name used for Venus in the second novel of the trilogy. These names are therefore easy to confuse with Thulcandra, but they identify different planets in Lewis’s fictional cosmology.
The naming system supports Lewis’s larger contrast between a damaged Earth and other worlds that remain connected to a spiritual order. The novel combines this speculative setting with themes involving science, imperialism, language, and Christian theology.