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Mudd, a class K planet

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, wind speeds of up to 312 meters per second, and an atmosphere consisting of methane, nitrogen, and liquid neon. (TNG: "The Royale")

Starfleet Transfer Regulations included provisions regarding special environmental support for class-K native personnel. (TNG-R: "The Measure Of A Man")

Starfleet Safety Protocols banned the use of the explosive ultritium 283 in class K planetary environments. (TNG-R: "Night Terrors")

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 information

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).

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