Vulcan (The Power of the Daleks)

Vulcan was a planet which supported a human colony.

Overview
Vulcan was roughly twelve parsecs away from any other colony. The atmosphere was breathable by humans. It had very little radiation and the average temperature was 30 degrees Celsius (86 degrees F). It was a young, volcanic world, with nutrient-rich soil, but with no native life. It had pools of fuming mercury. Vulcan's day was several hours shorter than Earth's.

History
Vulcan was colonised after humans discovered the mineral riches of the planet. It was the third such colony. The human colony was almost taken over by Daleks who had been found in a crashed spacecraft underground, then reactivated by a scientist called Lesterson. (DW: The Power of the Daleks)

The Seventh Doctor and Elizabeth Klein visited the mercury swamps of Vulcan prior to their arrival on the Vrill colony. (BFA: Survival of the Fittest)

Other information
Coincidentally, the name Vulcan was also given the home planet of Spock in the Star Trek television series, as indicated by Donna Noble's comparing of the Tenth Doctor's attempt to read a possessed Nazi soldier's mind with something a Vulcan (namely Spock) would do. (NSA: The Nemonite Invasion)

Behind the scenes

 * Scientists of the 19th and 20th centuries hypothesised the existence of a planet between the orbit of Mercury and Sol, and sometimes referred to that planet as Vulcan. This theory has since been discredited. EDA: The Taking of Planet 5 makes reference to this.
 * As noted above, the Star Trek character Spock came from the fictional planet Vulcan. Star Trek only just beat Doctor Who in introducing the concept of an alien world called Vulcan by a few weeks, as it debuted not quite two months before Power of the Daleks aired. The two shows seem to have selected the name independently.