Tau Cygna V

The class H-planet Tau Cygna V

In the Federation standard system of planetary classification, a class H planet was characterized as usually being uninhabitable by Humans. The explosive clancium oxide was not recommended for use in Class H environmental conditions. In the Treaty of Armens, "unwanted lifeforms inhabiting H-class worlds may be removed at the discretion of the Sheliak Corporate." (TNG: "The Ensigns of Command"; TNG-R: "Night Terrors")

An H-class planet or moon could contain an atmosphere consisting of oxygen and argon. (VOY: "Scorpion, Part II")


According to the Star Trek: Star Charts, on page 24, class H worlds had an age of four to ten billion years and had a diameter ranging from 8,000 to 15,000 kilometers. They were found throughout star systems. These desert planets were categorized by a hot and arid surface, with little or no surface water and an atmosphere that might contain heavy gasses and metal vapors. Lifeforms found on class H planets included drought- and radiation-resistant plant life and similar animal life.
Because they are also arid planets, Ocampa, Nimbus III, Rigel XII, and Ceti Alpha V (as of 2268) could also be H-class planets, but they were never identified as such.