Class K

In planetary classification, class K is used to describe planets that are adaptable for Humans by use of pressure domes and life-support systems. An example of a class K planet is Mudd. (TOS: "I, Mudd")

The transjovian subtype of this class is used for harsh planets such as Theta 116 VIII, with average surface temperatures well below 0 °C and an atmosphere consisting of methane, nitrogen and liquid neon (TNG: "The Royale").

Since this type of planet has a solid surface unlike a Jovian planet, the "transjovian" label probably refers to its orbital location relative to the Jovians in its system.

Background

According to the non-canon publication Star Trek: Star Charts, Class K planets are called Adaptable. These planets have an age that ranges from 4 to 10 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 solar 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.