In the Federation standard system of planetary classification, a class K (or K type) planet was characterized as being adaptable for Humans by use of pressure domes and life support systems. An example of a class K planet was Mudd. (TOS: "I, Mudd")
The transjovian subtype of this class was used for harsh planets such as Theta VIII, with average surface temperatures well below 0 °C and an atmosphere consisting of methane, nitrogen, and liquid neon. (TNG: "The Royale")
|D • H • J • K • L • M • N • R • T • Y • Other classes|
According to the non-canon publication Star Trek: Star Charts, class K planets are called "adaptable". These planets have an age that ranges from four to ten billion years and a diameter that ranges from 5,000 to 10,000 kilometers. A class K planet is found within the ecosphere of a star system. They are categorized by a barren surface with little or no surface water and a thin atmosphere comprised mainly of carbon dioxide. Lifeforms found on class K planets are limited to single-celled organisms, although class K planets can be adapted for humanoid life through the use of pressure domes. According to the criteria, Mars could be considered a class K planet (as could Tyrellia).