Iwa

Iwa was a planet in a single-star system.

Topography
Iwa had a barren surface, more rock than vegetation. In fact, when the Doctor's TARDIS landed on the planet, its chameleon circuit chose to turn the vehicle's exterior into a boulder out of deference to the craggy landscape. (PROSE: Frayed)

Meteorology
Rain was relatively uncommon on the planet, and when it came, it did so extraordinarily briefly. As a result, the air remained fairly saturated and humid. The sky itself was blue, indicating similar chemical composition and light refraction to Earth. (PROSE: Frayed)

History
Iwa was the location of a kind of penal colony which punished people for their potential crimes. It may be site of the first contact between the First Doctor and humans (PROSE: Frayed), other than the Earth's moon. (AUDIO: The Beginning) It was the location where Susan obtained the name "Susan", and the Doctor was first called "the Doctor". (PROSE: Frayed)

At some point in its history, Iwa was placed under the protection of the Galactic Heritage. (PROSE: The Tomorrow Windows)

Behind the scenes
Iwa means "rock" in Japanese.